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Queen Hippolyta is a fictional DC Comics superhero, based on the Amazon queen Hippolyta from Greek mythology. Introduced in 1941 during the Golden Age of Comic Books, she is the mother of Wonder Woman and Donna Troy, and queen of the Amazons of Themyscira.

Hippolyta (DC Comics)

The character Hippolyta (initially spelled "Hippolyte") first appeared in All Star Comics #8 (December 1941) in the same story that introduced her daughter, Princess Diana, known as Wonder Woman. Created by writer William Moulton Marston and artist Harry G. Peter, this original version of the character is a brunette like Diana.

In the story, Hippolyte and the Amazons once resided in "Amazonia" in the days of ancient Greece, until they were beguiled and bested by the demi-god Hercules, who had been inspired by the God of War Mars, to go after her. She was able to beat him thanks to the magic girdle, but he seduced her, and tricked her into removing the girdle, allowing him to steal it. This caused the Amazons to lose their super strength and the favor of their patron goddess, Aphrodite. Eventually she and the other Amazons were forgiven, but had to wear bracelets to remind them of the folly of submitting to men. To regain their status, the Amazons were decreed to leave the mortal world and relocate to Paradise Island. There they established their own society, free from the evils of man's world. So long as they remained there and Hippolyte retained possession of her magic girdle, the Amazons would be immortal. Much of this history was adapted, varied, and expanded upon in the modern version of the Wonder Woman comics.

For the most part, Hippolyte remained on Paradise Island during the Golden Age era, rarely interacting with the modern world to which her daughter had journeyed. Her role was that of the Amazon Queen and mentor to Wonder Woman. She was devoted to the Olympian goddesses, particularly the Amazons' patron Aphrodite, and was adamant that man never be allowed to set foot on Paradise Island. Although she remained mainly on the island, in one story from Sensation Comics #26 (reprinted in Wonder Woman: The Complete History), Hippolyte travels to Man's World and briefly assumes the role of Wonder Woman.[1] In the first appearance of Villany inc she is kidnapped to lure Wonder Woman into a trap.

In the late 1950s, DC Comics introduced the concept of the Multiverse, and the Golden Age Hippolyte was established as existing on the world known as Earth-Two. The last appearance of this incarnation of Hippolyte was in Wonder Woman (vol. 1) #97 in April 1958, after which the focus shifted from Earth-Two to the more modern versions of the characters on Earth-One.

As of Wonder Woman (vol. 1) #98 (May 1958), the Amazon Queen's name was spelled "Hippolyta", and she was depicted with blonde hair and a triple pointed tiara. The backstory of this Silver Age Hippolyta was largely identical to the Golden Age version, with some exceptions. For example, it was established in a 1973 storyline that Hippolyta had crafted a second daughter from clay, a dark-skinned Amazon named Nubia who was to be Wonder Woman's sister before she was spirited away by the god Mars.[2] Hippolyta was also the adoptive mother of Donna Troy, who had been rescued from a fire and brought to Paradise Island. As before, Hippolyta's role in the Silver Age era was primarily that of Paradise Island's queen and mentor to Wonder Woman. She was frequently shown interacting with her daughter as well as supporting characters of the era such as Wonder Girl and Wonder Tot. According to the DC Comics 1976 calendar, Hippolyta was born on January 8.

Hippolyta was also instrumental in several of the continuity shake-ups for the Earth-One Wonder Woman. Enraged that her daughter, recovering from amnesia, had submitted to trials by the Justice League to prove her worth to rejoin, she created her own test which involved resurrecting Steve Trevor to lead an assault on Paradise Island. The goddess Aphrodite granted Diana's wish to allow the resurrected Trevor to continue living (although he was later revealed to be Eros animating Trevor's body). After Trevor had again been killed and a grief-stricken Diana returned home, Hippolyta erased Diana's memories of him; when a Trevor from a parallel universe burst through the barriers between worlds and crashed off Paradise Island, Hippolyta asked Aphrodite to alter the memories of the entire world to allow the new Trevor to embark upon a life on Earth-One.

In 1985, the Crisis on Infinite Earths miniseries revised DC Comics continuity and combined the multiple Earths into one world. The modern version of Hippolyta would combine elements of her earlier incarnations and take on greater importance in the series.

Hippolyta's origins underwent a revision after writer George Pérez' revamp of Wonder Woman in 1987. In that continuity, Hippolyta and the rest of the Themyscirian Amazons were created by a select group of the Olympian gods, which included Artemis, Athena, Hestia, Demeter and Aphrodite. These goddesses reincarnated the souls of women gathered by the earth-goddess Gaea (women who had been slain by man's ignorance and fear). They sent these souls (Hippolyta's original incarnation was a pregnant cavewoman slain circa 32,000 BCE) to the bottom of the Aegean Sea. The souls then began to merge with the clay on the sea bed. The first reincarnated Amazon to break the surface was Hippolyta, and thus she was titled as Queen of the new race; in this version Hippolyta stood 5'9", weighed approximately 130 lbs, had curly black hair and more. The second Amazon to break the surface was her sister Antiope and she ruled at Hippolyta's side. Each of the goddesses then blessed the Amazon nation with gifts: hunting skills (Artemis), wisdom (Athena), warm homes (Hestia), plentiful harvests (Demeter), and beauty inside and out (Aphrodite). As a symbol of their rsponsibilities, the goddesses gave Hippolyta and Antiope each a Golden Girdle of Gaea. The Amazons eventually founded the city of Themyscira in Anatolia and became known as fierce warriors of peace in Turkey, Greece and Rome.

The jealous and vengeful god Ares tried to drive a wedge between Amazons and other civilizations by influencing his half-brother, the demi-god Heracles to challenge the Amazons. When Heracles first approached the Amazons seeking battle, Hippolyta met him outside the city gates and tried to employ peaceful negotiations. When this did not work, Heracles attacked the Amazon Queen. Hippolyta easily turned the tables on him by using her wisdom and battle skills to subdue him. Still wishing peace, Hippolyta invited Heracles and his men into their city to celebrate a potential friendship with a feast. Heracles seemingly accepted the invitation.

Once in their city, Heracles and his men drugged the Amazons' wine and took them prisoner. After the theft of Hippolyta's Golden Girdle and abuse and rape of the Amazons, Hippolyta cried out to Athena to help them escape their bonds. Athena said that she would only aid them on the condition that the Amazons not seek retribution against Heracles and his men as that would be beneath the ideals the Amazons. Hippolyta agreed and her bonds were broken. Hippolyta freed the other Amazons. The Amazons, however, were filled with hate and the desire for revenge. Breaking Hippolyta's oath to Athena, the Amazons began slaughtering their captors, (Heracles and his general Theseus had left).

After they had killed all the men keeping them prisoners, Antiope renounced all ties to the Olympian gods and said goodbye to her sister Hippolyta, giving Hippolyta her Golden Girdle of Gaea to replace the one stolen by Heracles. She left to pursue vengeance, intending to kill Heracles and Theseus. Antiope's tribe later became the Amazons of Bana-Mighdall.

Hippolyta and the remaining faithful Amazons then went to the sea shore where Athena told them their punishment for betraying their ideals. They were to be given immortality so that they could forever safeguard a doorway to a place of unspeakable evil. The doorway was on a far-off isolated island and it took months to get there. To guide their way, the god Poseidon cleared a pathway for them across the seas. Once they arrived, the Amazons created a new city and named their new home Themyscira, after their previous fallen city. The Amazons continued to live on the island guarding this "Doom's Doorway" (later shown to also lead to other places such as parts of Hades) and paying homage to their gods for three-thousand years.

Sometime after the 1940s, Hippolyta began to ache for something unknown. She was told by the oracle Menalippe that the yearning she felt was for her unborn daughter. She was instructed to go to the beach and form a figure of an infant out of the island's clay. The original five goddesses, plus Hermes, united to incarnate and bless this final soul. They imbued it with many gifts and merged it with the clay form and, just as with the previous Amazons, the clay was changed into flesh and blood. Hippolyta named the child Diana, after a "great and holy warrior," a stranger who had washed ashore on the island and died helping the Amazons defeat Cottus, a creature escaping Doom's Doorway. This Diana was later revealed to be the mother of Steve Trevor.

During Diana's Challenge of the Gods storyline,[3][4][5] she discovered that Heracles was transformed into a colossal stone pillar within Doom's Doorway, and was supporting Themyscira's weight for several millennia.[4] In this state he was tormented and scarred by various mythological creatures, feeling the pain inflicted by them but not being able to do anything about it (much like Prometheus).[5] This was the punishment given to him for his past transgressions. Thanks to Diana, Hippolyta, and the Lasso of Truth, he was restored to his original form and begged the Amazons for forgiveness. Though some of the Amazons still harbored anger for their past humiliation, most of them were moved by Heracles' newfound humility, and Queen Hippolyta asked her people to search their hearts for the strength to forgive, which they almost immediately did. Doing so herself, Hippolyta not only forgave Heracles, but shared a brief kiss with him before he left the mortal realm to return to his father in Olympus.[6]

After Diana's completion of her challenge, the Amazons were released from their punishment by the Olympian gods. They were free to live out their lives any way they saw fit while retaining their immortality.[6] To celebrate, Hippolyta declared that Themyscira would finally create cultural exchange with the outside world. Diana became Themyscira's ambassador to the U.N.[7][8]

In spreading the Amazon ideals of love and peace, Diana made a powerful enemy, the sorceress Circe.[9] One of Circe's attacks on Diana involved the brainwashing of Hippolyta, transforming her into the second Shim'Tar, or chief warrior, of the Amazons of Bana-Mighdall.[10][11] In this persona, Hippolyta attacked Diana, and was defeated by a ricochet from Diana's bracelets.

Circe considered all Amazons to be her enemy and later made a new plan for revenge. She teleported the Amazons of Bana-Mighdall to Themyscira on the pretense that they were to take the island. While the two groups fought, Circe teleported the island to a dimension of demons. There the two groups of Amazons were forced to put aside their rivalry in order to stave off the demons' attacks. The Amazons remained in the demon dimension until Diana discovered what had happened and forced Circe to return the island back to its rightful dimension.[12] They found upon their return that although their time in the demon dimension lasted several years, the time passed in our dimension was only a few months.[13]

In this time the Themyscirian and Bana-Mighdallian Amazons made an uneasy truce. The Themyscirians would live in the city while the Bana-Mighdallians would form their own settlement on the opposite side of the island. In Hippolyta's mind she still served as Queen over all Amazons on the island, but the Bana-Mighdallian Amazons did not see it as such and tensions between the two tribes remained.[14]

Because the demon dimension they were in was magic based, Hippolyta began to receive dreams and visions of the future. In one such dream she foresaw Wonder Woman's death. Fearful for her daughter's welfare, she put into motion a plan to remove Diana from her role as Wonder Woman and replace the title of Themyscira's Champion to another Amazon. Thus a new Contest for the title was made though she kept her true reasons for calling the new Contest to herself alone. Initially Hippolyta thought the Amazons of Bana-Mighdall were not worthy to enter the Contest but when Diana, angered at her mother's treatment of the new Amazons, called a vote on the whole to see if her people also agreed that they should be allowed to participate, the answer was yes. Suddenly inspired, Hippolyta noticed that the Bana-Mighdallian's most likely warrior to win was the Amazon Artemis. Hippolyta then in secret went to the Themyscirian Amazon mystic Magala. She had Magala transfer half of Diana's gods-given powers over to Artemis in order for Artemis' victory to be better equipped.[15] Hippolyta also provided many additional obstacles for Diana to encounter during her Contest trials in order for her to become sidetracked from the goal of winning. Due to her actions, Artemis became the Contest's winner and the new champion Wonder Woman. Later when Diana began to receive visions of the past she confronted her mother on why she really called for a new Contest. When Hippolyta told her she and Diana's relationship became scarred as Diana never truly forgave her mother for knowingly sending another Amazon to her death.[16]

After Artemis was killed in battle the title of Wonder Woman was returned to Diana. This sent Hippolyta into a deep depression as she realized she was the cause of an innocent's death. Hippolyta gave command to the Amazon General Philippus and went into self-imposed banishment.[17]

Hippolyta boarded a small boat and let it cast adrift. She eventually landed in Louisiana where she met a psychic named Angela.[18][19][20] After becoming friends with Angela and her family, Angela informed Hippolyta that her daughter was in serious danger.[21] Rushing to her aid, Hippolyta arrived too late to save Diana from the demon Neron, as Diana was still suffering from the spell that had reduced her strength.[15] Thus, Hippolyta's vision of her daughter dying as Wonder Woman came true.[22]

Diana, after her death, was granted divinity as the Goddess of Truth by her gods for such faithful devotion.[23] During her brief time as a god of Olympus, Diana was replaced in the role of Wonder Woman by her mother.[24] As opposed to Diana receiving the title in honor, Hippolyta's role as Wonder Woman was meant to be a punishment for her betrayal in Artemis' death as well as for unintentionally killing her own daughter.[25] However, Hippolyta eventually grew to enjoy the freedom and adventure the title came with. Whereas Diana used the Lasso of Truth as her primary weapon, Hippolyta favored a broad sword and wore a short blue skirt instead of briefs.

John Byrne, the writer that introduced the concept of Hippolyta as the first Wonder Woman, has explained his intentions in a post in his message board:

I thought George's one "mistake" in rebooting Wonder Woman was making her only 25 years old when she left Paradise Island. I preferred the idea of a Diana who was thousands of years old (as, if I recall correctly, she was in the TV series). From that angle, I would have liked to have seen Diana having been Wonder Woman in WW2, and be returning to our world in the reboot.

Not having that option, I took the next best course, and had Hippolyta fill that role.[26]

As Wonder Woman, Queen Hippolyta immediately got involved in a time travel mission back to the 1940s with Jay Garrick.[27] After this mission, she elected to join the Justice Society of America and remained in that era for eight years, where her teammates nicknamed her "Polly". During that time she had a relationship with Ted Grant.[28] Hippolyta also made visits into the past to see her godchild Lyta, daughter of Hippolyta's protege Helena, the Golden Age Fury.[volume & issue needed] These visits happened yearly from young Lyta's perspective and also accounted for Hippolyta's participation in the JSA/JLA team ups. When she returned from the past, Hippolyta took Diana's place in the JLA as well.[29][30]

Eventually Diana gave up her godhood and returned to her role as Wonder Woman.[31] Still clinging to her newfound sense of freedom, Hippolyta did not wish to relinquish her title as Wonder Woman (even though she admitted her daughter looked "better in a bathing suit" than she did), leaving two different Wonder Women acting in the same role at the same time. Diana was often unhappy with Hippolyta's continued role as Wonder Woman as she felt Hippolyta was ignoring her true duties as ruler of Themyscira, thus further inciting the antagonism between mother and daughter.[32]

Around this time Hippolyta discovered that the hero Donna Troy was actually a mirror image of her daughter Diana, brought to life through Themyscirian sorceries. Though Hippolyta had met Donna on previous adventures, when the two women met again after learning this fact, Hippolyta accepted Donna as a second daughter and held a coronation on the island, proclaiming Donna to be the second Amazon princess and an heir to the Themyscirian throne.[33]

On one visit to the island, Diana discovered that the two tribes of Amazons were on the verge of a civil war due to unresolved issues and mysterious acts of sabotage made on the Bana-Mighdallian's construction of their city. When both Diana and Donna confronted Hippolyta about her inaction of rule at such a dangerous time, Hippolyta became very upset with her two daughters and told them that she intended to continue her role as Wonder Woman in the outside world and that Diana and Donna were to rule the island in her absence. Unfortunately the civil war took place after all and many Amazons on both sides were killed. Returning to the island, Hippolyta and Diana agreed to denounce their royal titles in order for both Amazon tribes to have an opportunity for peace, having both tribes gain equal footing in united rule.[34][14]

Hippolyta continued to establish a distinguished career as Wonder Woman. The Queen enjoyed her role in the Justice Society and became accustomed to life in the United States. Mother and daughter fought on several occasions over Hippolyta's past expected roles — hero or queen — and their differences were unresolved when the queen sacrificed herself to save the Earth from Imperiex during the Imperiex War featured in Our Worlds at War.[35] Ironically Hippolyta died at the birthplace of the Amazons, near the Aegean Sea in Greece. However she was allowed to see her daughter one last time and say goodbye. She, the spirit of her sister Antiope, and Steve Trevor's mother Diana Rockwell Trevor became ghostly guardians of the island watching over both tribes as their distant and former queens.[36]

As part of the Amazons Attack storyline, the witch Circe revived Hippolyta and showed her that the U.S. government illegally kidnapped her daughter Diana.[37] She was being tortured until she gave over the plans on how the U.S. government could create their own Purple Ray to be used as a weapon.[38] Angered over this, Hippolyta resumed leadership of the Amazons and had them attack the city of Washington, D.C. in the hopes of rescuing Diana and serving their own form of justice against the world for their actions. They are shown using winged steeds, and other mythical creatures. During battle Hippolyta discovered that Circe had secretly planned to detonate a nuclear weapon on Themyscira and gained her revenge on the traitor by impaling the sorceress with a battle spear through the chest. Wonder Woman has an opportunity to kill her mother but does not take it, instead giving the knife to Hippolyta, who will not kill her daughter. Despite the fact that Circe is supposedly dead, Hippolyta seems fully intent on continuing her assault on the United States, even issuing an attack on other locations, including Kansas. Her more chaotic and malicious actions start to concern her Amazon generals. It is later learned that Circe used a portion of her own soul to revive Hippolyta from death. Because of this Hippolyta's persona was tainted by the witch's evil and thus Hippolyta is now a more blood-thirsty being than before.[39]

At the conclusion of the war all of the Amazons are given false identities and scattered throughout the world.[40][41] Hippolyta is spared but is banished to live alone on Themyscira, by what appears to be Athena but is later revealed to be the villainous Granny Goodness, who along with the other New Gods of Apokolips have imprisoned the Greek deities. In Countdown to Final Crisis, Hippolyta lives in hiding from Granny Goodness and her new brand of Amazons, human recruits being trained as a new generation of her Female Furies. With the help of island castaways Holly Robinson (briefly known as Catwoman), Harley Quinn and a powerless Mary Marvel, Hippolyta is able to drive Granny out of Thermiscyra and back to Apokolips. After the Greek Gods are freed by Mary, Granny is murdered by the mysterious Godkiller, leaving Hippolyta once more as the Queen of Themyscira.

During her isolation Hippolyta travels to the four corners of Themyscira, speaking to an Amazon prisoner at each point, asking them if they repent, to which each prisoner replies, "Never". However, the fourth and last prisoner, whom Hippolyta identifies as Alkyone, presents her with a wooden tiara with the words "Our Queen" across it similar to the one she and Diana both wore as Wonder Woman. Alkyone tells Hippolyta since she denied her the use of any blades, she gnawed in the inscription with her teeth. She goes on to accuse Hippolyta of betrayal for birthing "The Dragon", which clearly is a reference to Diana. Alkyone begs her to kill Diana and let them be a tribe again, but Hippolyta adamantly refuses. Alkyone then tells Hippolyta to tell Diana the truth, but again Hippolyta refuses and breaks the wooden tiara in half. As she leaves, Alkyone vows to save Hippolyta and make them a tribe again by killing Diana.[42]

Alkyone's past reveals her to have been a member of Hippolyta's Royal Guard along with three other Amazonsâ€”Myrto, Charis and Philomela, charged with her personal protection.[43] They were viewed as too brutal-minded and overzealous by General Philippus, captain of the General Amazon Guard, a viewpoint that was later proven when Alkyone learned that Hippolyta desired a child. This came to a head when Alkyone learned from the Amazon sorceress, Magala that another Amazon named Gennes had supposedly given birth to a daughter. But it turned out the baby was nothing more than a clay doll carved in the image of a child. Concluding Gennes had gone mad, Alkyone ordered that no such dolls were ever to be crafted on Themyscira again. After that, she ordered Gennes to be killed. In the present day, the army of Captain Nazi lands on Themyscira, intending to claim it for themselves. Alerted to their arrival, Hippolyta cuts her hair and readies herself for battle and vows to redeem herself for all the mistakes she has made since her resurrection. Elsewhere on the island, Alkyone offers her help and the rest of the former Royal Guard to the soldiers in hunting down Hippolyta in exchange for their release.

In Wonder Woman issues 24 and 25, there is a movie being made about Diana. In the beginning of issue 24, Diana brings Thomas Andrew Tresser home to meet her mother, Queen Hippolyta. Hippolyta takes Tresser and leaves Diana alone on the beach. This is her opportunity to get to know the man in whom her daughter has become interested. The getting to know him phase includes taking Tom to the Royal Menagerie to hand feed Griffins of Myth. While there Hippolyta asks rather directly if he and Diana have made love yet. Flustered he is able to honestly answer that they haven't. She asks Tom, "Will you protect her, keep her from harm, if you are able?" He replies, "Yes. That I can promise. Although it usually goes the other way 'round, to be blunt." Before he leaves she gives him a spear she has made, grants him the title Sir Thomas of Cleveland, and makes him a guardsman of Themyscira. As Diana and Tom prepare to leave she requests one thing of her new guardsman, babies. As many as he and Diana can create as quickly as they can create them. As they leave the island Alkyone is seen watching them from shore as they float away on a giant shell.[44]

Following the events of Wonder Woman #600, the timeline is altered by the Greek Gods and Hippolyta's history is radically changed once again. Here, Themyscira is invaded by a heavily armed paramilitary group while Diana is still a child, and the majority of the Amazons are wiped out in the ensuing battle. Hippolyta is able to save Diana by entrusting her to several of her servants, who smuggle the child to the United States in the midst of the attack, but Hippolyta herself is ultimately captured by the enemy soldiers. After being bound and presented to the leader of the invaders, Hippolyta commits suicide by throwing herself into a massive fire being used to incinerate the dead Amazons, choosing to die rather than submit to her captors.[45] After Wonder Woman's exile in the altered continuity is reversed, Hippolyta is briefly restored to her Modern Age origins,[46] greeting her daughter back and approving the changes she had done to her attitude and appearance during her ordeal.

Following a new reset of the DCU continuity, Hippolyta receives another major change. Now looking like the Silver Age Hippolyta, youthful and blonde, she retains her edgy, warrior woman attitude. Furthermore, this incarnation of Hippolyta didn't fashion Diana from clay: instead, she bore her daughter from a relationship with Zeus, concocting a lie to protect Diana from Hera's rage.[47]

After the truth about Diana's birth is revealed, Hera, the queen of the Greek gods, appears on Paradise Island to punish Hippolyta (not for having an affair with her husband, but for having been too weak to resist Zeus' seduction). Hippolyta had predicted this, and asks Hera to take her life in exchange of letting Diana live. However, Hera changes her mind at the last second, and instead of killing Hippolyta, turns her into stone and the rest of the Amazons, minus Diana, into snakes, thus destroying Wonder Woman's home and her only family.[48]

During the relaunch, Hippolyta once again goes through a major change. In the "Year One" storyline Hippolyta is presented like the Golden Age version with black hair and has a peaceful demeanor. When Steve Trevor lands on the island and is the only survivor of the soldiers, she seeks to have him sent home safely by hosting a competition to determine which Amazon is worthy. She quickly realizes her daughter will be the one to win, something that saddens her since leaving the island forsakes an Amazon's right to return. However, she is nevertheless proud when Diana does indeed win, and they bid each other goodbye.

In the story arc "The Lies" Wonder Woman and Steve seemingly return to Themyscira to find Hippolyta (the New 52 one) and the Amazons safe and sound, despite Wonder Woman remembering her apparent demise. Hippolyta does not understand what she means and only seems suspicious of Steve, telling Diana not to let him wander around alone. However, Diana and Steve begin to notice the inconsistencies: the Amazons are not familiar, they speak English instead of their ancient language, and their architecture has changed. Diana realizes this is because what she thought to be true was a lie: she never returned to Themyscira when she left years before, so the New 52 Hippolyta was just a kind of illusion.

In the present day, Hippolyta and the Amazons take notice of a strange tree growing on the island that serves as a bad omen of events to come. Any attempts to cut down the tree are futile, and Hippolyta worries Diana is in danger. She and her fellow Amazons go to the tree and combat Deimos and Phobos, Ares' sons in wolf-like forms before they are defeated on the other side by Diana. Hippolyta is briefly reunited with her daughter but unable to reach her, stating how proud she is of who Diana has become.

Hippolyta has 3,000 years of combat experience, providing her expertise in both hand-to-hand combat as well as with hand-held weapons. As a Themyscirian Amazon she is ageless and immortal, allowing her to live indefinitely without physically aging beyond her youthful prime, but is still vulnerable to death upon sufficient injuries and such.[35][49] She also possesses enhanced strength and intelligence. As shown by fellow members of her tribe, she has the capability to break apart steel and concrete with her bare hands,[34][50] jump over 12 feet from a standing position,[51] has a high durability factor,[52] enhanced healing,[53] and the ability to absorb and process a vast amount of knowledge in a short period of time.[54]

Hippolyta, also in addition to all the Themyscirian Amazons, possesses the ability to relieve her body of physical injury and toxins by becoming one with the Earth's soil and then reforming her body whole again.[53] The first time Diana does this she prays to her god Gaea saying: "Gaea, I pray to you. Grant me your strength. You are the Earth who suckled me, who nurtured and bred me. Through you all life is renewed. The circle which never ends. I pray you, mother Gaea, take me into your bosom. Please, let me be worthy." During writer John Byrne's time on the comic it was stated that this is a very sacred ritual to the Themyscirians, only to be used in the most dire of circumstances.[55]

As an Amazon, Hippolyta had access to a number of magical artifacts. These artifacts included the Gauntlet of Atlas, which greatly increased her overall strength and durability, as well as the Sandals of Hermes, which increased her speed and allowed her to fly. During her time as Wonder Woman, Hippolyta wielded the Lasso of Truth, though she seemed to prefer a broadsword and shield in combat. Her broadsword was created by Hephaestus and was sharp enough to slice the electrons off of an atom.

In the alternate timeline of the Flashpoint event, Hippolyta encourages Aquaman of Atlantis to marry her daughter, Wonder Woman, after she had been poisoned by a Kraken. On the wedding day, however, Hippolyta was murdered by Artemis in disguise as an Atlantean, who in an act of betrayal, was working with Ocean Master. Diana was actually the target, but Hippolyta took the arrow. This leads to war between the Amazons and Atlanteans.[56]

In the prequel comic to the video game, Hippolyta first appears in Year Two to take her comatose daughter Diana back to Themyscira with the hope that she will be healed. In Year Three, when Diana does not awake even after physically healing, she makes a deal with Hera to awaken Diana if she agrees to an eventual favor. Hera calls upon the favor in Year Four when she orders Hippolyta to lead the Amazons on an attack on Superman and his Regime. Hippolyta is reluctant since Diana is a part of the Regime, and when she refuses she is imprisoned by Hera and Zeus. Eventually she is sent to Tartarus with Harley Quinn and Billy Batson (Shazam), though Harley breaks them out with the use of a Kryptonian super pill and her own bizarre behavior. They are confronted by Ares, though they get away because of a Mother Box. They are then confronted by Darkseid, who imprisons them and reveals that he is aligned with Ares. Superman appears and frees them, leaving them open to flee with the Mother Box to the Himalayas, where they are met by Wonder Woman and Batman. She later joins her daughter in combating the Greek Gods, though the threat of a nuclear bomb stops the fighting. Once Diana takes care of it the New God Highfather intervenes and convinces Zeus and the other gods to leave Earth alone; they agree with the promise of severing all ties, including with the Amazons. In the beginning of Year Five Hippolyta comforts a guilt-ridden Diana and reveals her knowledge of how Diana has romantic feelings for Superman. She encourages her to stand by his side.


the depth of the wave base is approximately

In seawater, the water particles are moved in a circular orbital motion when a wave passes. The radius of the circle of motion for any given water molecule decreases exponentially with increasing depth. The wave base, which is the depth of influence of a water wave, is about half the wavelength.

Wave base

The wave base, in physical oceanography, is the maximum depth at which a water wave's passage causes significant water motion. For water depths deeper than the wave base, bottom sediments and the seafloor are no longer stirred by the wave motion above.[1]

At depths greater than half the wavelength, the water motion is less than 4% of its value at the water surface[2] and may be neglected.

For example, in a pool of water 1 metre (3.3 ft) deep, a wave with a 3 metres (9.8 ft) wavelength would be moving the water at the bottom. In the same pool, a wave with a wavelength of 0.5 metres (1.6 ft) would not be able to cause water movement on the bottom.

There are typically two wave bases, the fair weather wave base (FWWB) and the storm wave base (SWB).[1]

The fair weather wave base refers to the depth beneath the waves under normal conditions and the portion of the seafloor that is agitated by this everyday wave action is known as the Upper shoreface.

The storm wave base refers to the depths beneath storm-driven waves and can be much deeper. The portion of the seafloor that is only agitated by storm-driven wave action is known as the Lower shoreface.

Note that another classification exists, which considers that the zone affected by both fair weather and storm waves is to be defined as shoreface, whereas Upper offshore is the name given to the zone only affected by storm waves and Lower offshore a zone not disturbed by any surface wave. (e.g. [3])


where does the last name camp come from

Camp is an English surname taken from Latin roots. The name is found in Great Britain and in other places throughout the world settled by the English. According to the 2000 census there are fewer than 1300 Camps in the UK.[1] The 2000 US census puts the number at over 27,000, making it the 1087th most common name in America, after McDermott.[2] The Australian government currently reports 465 persons named Camp.[3] The governments of Canada, New Zealand, and South Africa do not currently provide lists of surnames as the UK and others do. Totals outside the English-speaking world are also unknown.

Camp (surname)

People with the surname Camp have no single origin or ancestor, the name instead having been chosen by different families over a few centuries.[4] The name is sometimes a variant spelling of "Kemp", which comes from the Old West Germanic "kampo-z", meaning "a contest, or fight", which in turn became the Old English "kemp", for a "fighter" or "soldier."[5][6] However, the name usually denotes a family whose house was on an open field, or "camp", rather than in the woods or elsewhere.[7] The word was borrowed from the Middle French "camp", its first use in English, in 1528, being for a "place where an army lodges temporarily", only later transferring to a non-military use sometime after 1560. The French "camp" (later "champ") is itself derived from the Latin "campus", which also meant an "open field", but also and especially an "open space for military exercise". Coincidentally, the word's martial sense had been borrowed by the Germanic tribes during their conflicts with the Romans to become the aforementioned "kampo-z".[5]

Throughout the English-speaking world, but especially the United States, the name is sometimes derived from other, often longer, European names (e.g. the Italian "Campesi" or the Dutch "Van de Kamp") which were changed during the process of cultural assimilation. Camp can also be a shortening or anglicizing of similar French names, such as "de Camp" and "du Camp".


who plays danny on the new hawaii five o

Scott Andrew Caan (born August 23, 1976) is an American actor. He currently stars as Detective Danny "Danno" Williams in the CBS television series Hawaii Five-0 (2010–present), for which he was nominated for a Golden Globe Award. Caan is also known for his recurring role as manager Scott Lavin in the HBO television series Entourage (2009–2011). He was also a part of 1990s rap group The Whooliganz with The Alchemist. The duo went by the names Mad Skillz and Mudfoot, respectively.

Scott Caan

Caan was born in Los Angeles, California, the son of actor James Caan and Sheila Marie Ryan, an actress and former model.[1][2] His paternal grandparents were Jewish immigrants from Germany.[3] He has an older half-sister named Tara Caan and three younger half-brothers named Alexander James Caan (born 1991), Jacob Nicholas Caan (born 1995), and James Arthur Caan (born 1998).

Caan was a roadie for the rap groups Cypress Hill and House of Pain. Caan was also a member of the hip-hop group The Whooliganz (with producer and fellow MC the Alchemist).[4] The Alchemist and he, when performing as the rap duo the Whooliganz in the early '90s, received a record deal with Tommy Boy records. They recorded the album Make Way for the W., but after their first single "Put Your Handz Up",[5] the album was shelved and the duo was dropped by Tommy Boy. In 1995, the Whooliganz' song "Whooliganz" was released as a single in the UK, but Caan and the Alchemist had already parted ways. Caan reunited with his former partner The Alchemist in 2014 on the Step Brothers project Lord Steppington, performing in the song "Byron G" with musician Evidence.

After enrolling at the Playhouse West acting school in Los Angeles, Caan began acting in the late 1990s, appearing in a number of independent films and low-budget films. His first role in a major motion picture was that of Charlie Tweeder, a reckless Texas football player in Varsity Blues (1999). In the same year, he played the role of Drew in the film Saturn (also known as Speed of Life). Caan subsequently appeared in several studio films, including Ready to Rumble (2000) co-starring David Arquette, Boiler Room (2000) co-starring Vin Diesel, "Gone in 60 seconds" (2000) as Tumbler and American Outlaws (2001), co-starring Colin Farrell, in which Caan played 19th-century outlaw Cole Younger. In 2003, Caan made his directorial debut with the film Dallas 362, which subsequently won a prize at the 2003 Las Vegas Film Festival.

Caan appeared in the feature film trilogy Ocean's Eleven, Ocean's Twelve, and Ocean's Thirteen. In 2005, he co-starred with Paul Walker (with whom he appeared in Varsity Blues) in the action film Into the Blue. Caan wrote and directed the 2006 comedy The Dog Problem, and appeared as a supporting character in the film as well. He appeared on the television series Entourage in a recurring role as talent manager Scott Lavin from seasons six to eight.[6]

Caan plays Detective Danny "Danno" Williams in Hawaii Five-0 (a re-imagining of the 1968 Hawaii Five-O television series). The new series premiered on September 20, 2010, and in 2011 he was nominated for a Golden Globe Award for Best Supporting Actor – Series, Miniseries or Television Film for his performance.[7]

BuddyTV ranked him 95th on its list of "TV's Sexiest Men of 2011".[8]

In addition to acting, Caan has also pursued a career in photography.[9] Inspired and trained by cinematographer Phil Parmet while working together on the 2003 film Dallas 362, Caan has been shooting ever since. "In preparing for the film," Caan said, "Phil inspired me to learn about lenses, lights, frames, and the operation of a 250 millimeter camera. By the time the film was over, I wanted to shoot the next one."[10] In 2009, he published his first collection of photographs in a 256-page book entitled Scott Caan Photographs, Vol. 1. The book was edited and designed by Howard Nourmand, and includes an introduction by Steve Olson.[11]

Caan has been an active volunteer with Surfers Healing, an organization which introduces children with autism to the joy of surfing, as well as similar groups such as A Walk On Water, TheraSURF, and Life Rolls On.[12]

Caan is a black belt in Brazilian jiu-jitsu.[13] In 2014, it was announced that Caan and his girlfriend, Kacy Byxbee, were expecting their first child, and in July of that year, their daughter Josie James was born.[14]


what turns a natural hazard into a natural disaster

Many geophysical hazards are related;[5] for example, submarine earthquakes can cause tsunamis, and hurricanes can lead to coastal flooding and erosion. Floods and wildfires can result from a combination of geological, hydrological, and climatic factors. It is possible that some natural hazards are intertemporally correlated as well.[5][6] An example of the division between a natural hazard and a natural disaster is that the 1906 San Francisco earthquake was a disaster, whereas living on a fault line is a hazard. Some natural hazards can be provoked or affected by anthropogenic processes (e.g. land-use change, drainage and construction).[7]

Natural hazard

A natural hazard[1] is a natural phenomenon that might have a negative effect on people or the environment. Natural hazard events can be grouped into two broad categories,[2]which are Geophysical hazards[3][4] encompass geological and meteorological phenomena such as earthquakes, volcanic eruption, wildfire, cyclonic storms, flood, drought, and coastal erosion. Biological hazards can refer to a diverse array of disease and infestation.

An avalanche occurs when a large snow (or rock) mass slides down a mountainside.[8] An avalanche is an example of a gravity current consisting of granular material. In an avalanche, lots of material or mixtures of different types of material fall or slide rapidly under the force of gravity. Avalanches are often classified by the size or severity of consequences resulting from the event.[9]

An earthquake is the sudden release of energy stored as lithospheric stress that radiates seismic waves. At the Earth's surface, earthquakes may manifest with a shaking or displacement of the ground; when the earthquake occurs on the seafloor, the resulting displacement of water can sometimes result in a tsunami. Most of the world's earthquakes (90%, and 81% of the largest) take place in the 40,000-km-long, horseshoe-shaped zone called the circum-Pacific seismic belt, also known as the Pacific Ring of Fire, which for the most part bounds the Pacific Plate.[10] Many earthquakes happen each day, few of which are large enough to cause significant damage.

Coastal erosion is a physical process by which shorelines in coastal areas around the world shift and change, primarily in response to waves and currents that can be influenced by tides and storm surge.[11] Coastal erosion can result from long-term processes (see also beach evolution) as well as from episodic events such as tropical cyclones or other severe storm events.

A lahar is a type of natural event closely related to a volcanic eruption, and involves a large amount of material originating from an eruption of a glaciated volcano, including mud from the melted ice, rock, and ash sliding down the side of the volcano at a rapid pace. These flows can destroy entire towns in seconds and kill thousands of people, and form flood basalt. This is based on natural events.

A landslide is a mass displacement of sediment, usually down a slope.[12]

A sinkhole is a localized depression in the surface topography, usually caused by the collapse of a subterranean structure such as a cave. Although rare, large sinkholes that develop suddenly in populated areas can lead to the collapse of buildings and other structures.

A volcanic eruption is the point in which a volcano is active and releases its power, and the eruptions come in many forms. They range from daily small eruptions which occur in places like Kilauea in Hawaii, to megacolossal eruptions (where the volcano expels at least 1,000 cubic kilometers of material) from supervolcanoes like Lake Taupo (26,500 years ago) and Yellowstone Caldera. According to the Toba catastrophe theory, 70 to 75 thousand years ago, a supervolcanic event at Lake Toba reduced the human population to 10,000 or even 1,000 breeding pairs, creating a bottleneck in human evolution. Some eruptions form pyroclastic flows, which are high-temperature clouds of ash and steam that can travel down mountainsides at speed exceeding an airliner.

A blizzard is a severe winter stormer icy and windy conditions characterized by low temperature, strong wind and heavy snow.

Scientists warn that global warming and climate change may result in more extensive droughts in coming years. These extensive droughts are likely to occur within the African continent due to its very low precipitation levels and high climate.

A hailstorm is a natural hazard where a thunderstorm produces numerous hailstones which damage the location in which they fall. Hailstorms can be especially devastating to farm fields, ruining crops and damaging equipment.

A heat wave is a hazard characterized by heat which is considered extreme and unusual in the area in which it occurs. Heat waves are rare and require specific combinations of weather events to take place, and may include temperature inversions, katabatic winds, or other phenomena. There is potential for longer-term events causing global warming, including stadial events (the opposite to glacial "ice age" events), or through human-induced climatic warming.

Hurricane, tropical cyclone, and typhoon are different names for the same phenomenon: a cyclonic storm system that forms over the oceans. It is caused by evaporated water that comes off of the ocean and becomes a storm. The Coriolis effect causes the storms to spin.74 mph (119 km/h). Hurricane is used for these phenomena in the Atlantic and eastern Pacific Oceans, tropical cyclone in the Indian, and typhoon in the western Pacific.

An ice storm is a particular weather event in which precipitation falls as ice, due to atmosphere conditions. It causes damage.

A tornado is a natural disaster resulting from a thunderstorm. Tornadoes are violent, rotating columns of air which can blow at speeds between 50 mph (80 km/h) and 300 mph (480 km/h), and possibly higher. Tornadoes can occur one at a time, or can occur in large tornado outbreaks associated with supercells or in other large areas of thunderstorm development. Waterspouts are tornadoes occurring over tropical waters in light rain conditions.

Climate change can increase or decrease weather hazards, and also directly endanger property due to sea level rise and biological organisms due to habitat destruction.

Geomagnetic storms can disrupt or damage technological infrastructure, and disorient species with magnetoception.

A flood results from an overflow of water beyond its normal confines of a body of water such as a lake, or the accumulation of water over land areas.[13]

Wildfire is a fire that burns in an uncontrolled and unplanned manner. Wildfires can result from natural occurrences such as lightning strikes or from human activity.[14]

Disease is a natural hazard that can be enhanced by human factors such as urbanization or poor sanitation. Disease affecting multiple people can be termed an outbreak or epidemic.

In some cases, a hazard exists in that a human-made defense against disease could fail, for example through antibiotic resistance.

Each of the natural hazard types outlined above have very different characteristics, in terms of the spatial and temporal scales they influence, hazard frequency and return period, and measures of intensity and impact. These complexities result in "single-hazard" assessments being commonplace, where the hazard potential from one particular hazard type is constrained. In these examples, hazards are often treated as isolated or independent. An alternative is a "multi-hazard" approach which seeks to identify all possible natural hazards and their interactions or interrelationships.[15][5]

Many examples exist of one natural hazard triggering or increasing the probability of one or more other natural hazards. For example, an earthquake may trigger landslides, whereas a wildfire may increase the probability of landslides being generated in the future.[5] A detailed review of such interactions across 21 natural hazards identified 90 possible interactions, of varying likelihood and spatial importance.[5] There may also be interactions between these natural hazards and anthropic processes.[16] For example, groundwater abstraction may trigger groundwater-related subsidence.[17]

Effective hazard analysis in any given area (e.g., for the purposes of disaster risk reduction) should ideally include an examination of all relevant hazards and their interactions. To be of most use for risk reduction, hazard analysis should be extended to risk assessment wherein the vulnerability of the built environment to each of the hazards is taken into account. This step is well developed for seismic risk, where the possible effect of future earthquakes on structures and infrastructure is assessed, as well as for risk from extreme wind and to a lesser extent flood risk. For other types of natural hazard the calculation of risk is more challenging, principally because of the lack of functions linking the intensity of a hazard and the probability of different levels of damage (fragility curves).[18] ThinkHazard! is an online tool that provides an overview of the hazards from eight natural hazards (river floods, earthquakes, water scarcity, cyclones, coastal floods, tsunamis, volcanoes and landslides) developed by the Global Facility for Disaster Reduction and Recovery in partnership with other institutions.[19][20]

In 2000, the United Nations launched the International Early Warning Programme to address the underlying causes of vulnerability and to build disaster-resilient communities by promoting increased awareness of the importance of disaster risk reduction as an integral component of sustainable development, with the goal of reducing human, economic and environmental losses due to hazards of all kinds (UN/ISDR, 2000). The 2006-2007 United Nations International Disaster Reduction Day theme is “Disaster reduction education begins in school”. The Foundation of Public Safety Professionals has launched an international campaign giving everybody a chance to have their say, thought their international open essay or documentary competition “Disaster Risk Reduction Education Begins at School”.[citation needed]


who wrote the song try and catch the wind

"Catch the Wind" is a song written and recorded by British singer-songwriter Donovan. It was released as a single in the United Kingdom on March 12, 1965 through Pye Records (Pye 7N 15801) and a few months later in the United States through Hickory Records (Hickory 45-1309). The single was backed with "Why Do You Treat Me Like You Do?" on both the United Kingdom and United States releases. The melody of the song was influenced by "Chimes of Freedom" by Bob Dylan.[citation needed]

Catch the Wind

"Catch the Wind" was the first release by Donovan. It reached No.4 in the United Kingdom singles chart and No.23 in the United States Billboard Hot 100.[1] The single version featured Donovan's vocals with echo and a string section. The song was re-recorded for Donovan's first album What's Bin Did and What's Bin Hid, without the vocal echo and strings and with a harmonica solo added.

When Epic Records was compiling Donovan's Greatest Hits in 1968, the label was either unable or unwilling to secure the rights to the original recordings of "Catch the Wind" and Donovan's follow-up single, "Colours". Donovan re-recorded both songs for the album, with a full backing band including Big Jim Sullivan playing guitar and Mickie Most producing.


who played elf in lord of the rings

Bret McKenzie, half of the musical comedy duo Flight of the Conchords and a Wellington native, first landed a small role as an extra in The Lord of the Rings: The Fellowship of the Ring.[1] He appears sitting next to Aragorn during the council in Rivendell scene. When it is decided that the Ring must be destroyed, Frodo offers to take the Ring to Mordor, and Elrond proclaims the formation of the Fellowship of the Ring. The elf was dubbed "Figwit" by Tolkien fan Iris Hadad; after seeing Frodo agree to take the ring, saying "I will take it", the film switches to a shot where Figwit can be seen standing on the far right, and Hadad's initial reaction was "Frodo is grea...who is THAT?!?"[2] Later, Hadad corresponded with her university friend Sherry de Andres, and the two created the first Figwit fan website, www.figwitlives.net, calling him "Legolas for the thinking woman".[3][4]

Figwit

Figwit is a fan-created name for an unnamed Elven escort in Peter Jackson's The Lord of the Rings film trilogy, played by actor and musician Bret McKenzie of Flight of the Conchords fame. The name Figwit derives from an acronym for "Frodo is great...who is THAT?!?"  [sic].

McKenzie appeared as Figwit again in the third film, The Lord of the Rings: The Return of the King, where he was credited as "Elf Escort". He appears in the scene where Arwen is leaving for the Grey Havens and has a vision of her future son, Eldarion, this time with two lines warning her to not delay and then exclaiming as she turns around. Director Peter Jackson stated in the DVD commentary for The Return of the King that Figwit was called back and given dialogue in the third film "just for fun for the fans" because "so much fuss has been made about him over the last couple of years".[5]

In the film version of The Hobbit, McKenzie was cast as Lindir, an elf of Rivendell who appeared briefly in J.R.R. Tolkien's novel, The Fellowship of the Ring.[6]

Though he only appeared for about three seconds in the first film, Figwit's popularity soon blossomed, with Hadad stating that "[the fan site] got a lot of e-mails from people who thought they were the only ones who had noticed that handsome, dark-haired elf".[7] Figwit's physical appearance and demeanor are the source of much of his popularity: he has been noted for his "lithe and graceful" movement,[8] "enigmatic broodiness", "haughty demeanor", and "pouty" looks.[3] His fan website proclaims him "in a word, gorgeous. Or another, stunning... hypnotic... stupendous... captivating... take your pick."[2][9]

McKenzie has stated that the Figwit obsession is "weird," though he is "flattered."[10] He has remarked that "it's so hilarious because it's been propelled by so littleÂ ... I'm famous for doing nothing."[8][11]

Figwit does not appear in Tolkien's writings and was created exclusively for the films; thus there is little authentic information regarding him, save that he was an escort. The only "official" place where the name Figwit is used is on several Topps trading cards, including a The Return of the King series card, titled "Return to Rivendell," and an Authentic Autographs card featuring the signature of actor Bret McKenzie.[12] In The Lord of the Rings Trading Card Game he was assigned the name of Aegnor, one of Galadriel's brothers in The Silmarillion. A Figwit action figure was also created, though it was named "Elven Escort," as in the film.[13]

Figwit has been a subject of poetry, art, and fiction.[9] He is also a subject in slash fan fiction, where he is named "Melpomaen", a rough, literal Elvish translation of "fig" and "wit," derived from melpo, the Quenya word for fruit (fig),[14] and maen, the Noldorin word for clever or skilled.[15]

In 2004, a 57-minute documentary on the Figwit phenomenon was created by McKenzie's fiancÃ©e (and now wife) Hannah Clarke[16] and friends Stan Alley and Nick Booth. Entitled Frodo Is Great... Who Is That?!!, it premiered at the Auckland International Film Festival on July 23.[17] Meant to "[unravel] Bret's identity",[17] it follows McKenzie to the Edinburgh Festival Fringe, where he meets the fans of his trademark pout and "elvish good looks", and features extensive interviews with fans behind various Figwit fan sites as well as with Peter Jackson, Barrie Osborne, Mark Ordesky, Ian McKellen, and other cast members.[8][18] Booth stated that their film was "much more irreverent and strange" compared to other behind-the-scenes documentaries of the film trilogy, which were "very much driven around the production and the cast and Tolkien".[17]


what are the different types of heat transfer

Common types of heat exchanger flows include parallel flow, counter flow, and cross flow. In parallel flow, both fluids move in the same direction while transferring heat; in counter flow, the fluids move in opposite directions; and in cross flow, the fluids move at right angles to each other. Common constructions for heat exchanger include shell and tube, double pipe, extruded finned pipe, spiral fin pipe, u-tube, and stacked plate.[further explanation needed]

Heat transfer

Heat transfer is a discipline of thermal engineering that concerns the generation, use, conversion, and exchange of thermal energy (heat) between physical systems. Heat transfer is classified into various mechanisms, such as thermal conduction, thermal convection, thermal radiation, and transfer of energy by phase changes. Engineers also consider the transfer of mass of differing chemical species, either cold or hot, to achieve heat transfer. While these mechanisms have distinct characteristics, they often occur simultaneously in the same system.

Heat conduction, also called diffusion, is the direct microscopic exchange of kinetic energy of particles through the boundary between two systems. When an object is at a different temperature from another body or its surroundings, heat flows so that the body and the surroundings reach the same temperature, at which point they are in thermal equilibrium. Such spontaneous heat transfer always occurs from a region of high temperature to another region of lower temperature, as described by the second law of thermodynamics.

Heat convection occurs when bulk flow of a fluid (gas or liquid) carries heat along with the flow of matter in the fluid. The flow of fluid may be forced by external processes, or sometimes (in gravitational fields) by buoyancy forces caused when thermal energy expands the fluid (for example in a fire plume), thus influencing its own transfer. The latter process is often called "natural convection". All convective processes also move heat partly by diffusion, as well. Another form of convection is forced convection. In this case the fluid is forced to flow by use of a pump, fan or other mechanical means.

Thermal radiation occurs through a vacuum or any transparent medium (solid or fluid). It is the transfer of energy by means of photons in electromagnetic waves governed by the same laws.[1]

Heat is defined in physics as the transfer of thermal energy across a well-defined boundary around a thermodynamic system. The thermodynamic free energy is the amount of work that a thermodynamic system can perform. Enthalpy is a thermodynamic potential, designated by the letter "H", that is the sum of the internal energy of the system (U) plus the product of pressure (P) and volume (V). Joule is a unit to quantify energy, work, or the amount of heat.

Heat transfer is a process function (or path function), as opposed to functions of state; therefore, the amount of heat transferred in a thermodynamic process that changes the state of a system depends on how that process occurs, not only the net difference between the initial and final states of the process.

Thermodynamic and mechanical heat transfer is calculated with the heat transfer coefficient, the proportionality between the heat flux and the thermodynamic driving force for the flow of heat. Heat flux is a quantitative, vectorial representation of heat-flow through a surface.[2]

In engineering contexts, the term heat is taken as synonymous to thermal energy. This usage has its origin in the historical interpretation of heat as a fluid (Caloric) that can be transferred by various causes,[3] and that is also common in the language of laymen and everyday life.

The transport equations for thermal energy (Fourier's law), mechanical momentum (Newton's law for fluids), and mass transfer (Fick's laws of diffusion) are similar,[4][5] and analogies among these three transport processes have been developed to facilitate prediction of conversion from any one to the others.[5]

Thermal engineering concerns the generation, use, conversion, and exchange of heat transfer. As such, heat transfer is involved in almost every sector of the economy.[6] Heat transfer is classified into various mechanisms, such as thermal conduction, thermal convection, thermal radiation, and transfer of energy by phase changes.

The fundamental modes of heat transfer are:

Conduction or diffusion

By transferring matter, energy—including thermal energy—is moved by the physical transfer of a hot or cold object from one place to another.[7] This can be as simple as placing hot water in a bottle and heating a bed, or the movement of an iceberg in changing ocean currents. A practical example is thermal hydraulics.[citation needed] This can be described by the formula:

where Q is heat flux (W/m²), ρ is density (kg/m³),

c

p

{\displaystyle c_{p}}

 is heat capacity at constant pressure (J/kg·K), ΔT is the change in temperature (K),

v

{\displaystyle v}

 is velocity (m/s).

On a microscopic scale, heat conduction occurs as hot, rapidly moving or vibrating atoms and molecules interact with neighboring atoms and molecules, transferring some of their energy (heat) to these neighboring particles. In other words, heat is transferred by conduction when adjacent atoms vibrate against one another, or as electrons move from one atom to another. Conduction is the most significant means of heat transfer within a solid or between solid objects in thermal contact. Fluids—especially gases—are less conductive. Thermal contact conductance is the study of heat conduction between solid bodies in contact.[8] The process of heat transfer from one place to another place without the movement of particles is called conduction. Example: Heat transfer through Metal rods.[clarification needed] Steady state conduction (see Fourier's law) is a form of conduction that happens when the temperature difference driving the conduction is constant, so that after an equilibration time, the spatial distribution of temperatures in the conducting object does not change any further.[9] In steady state conduction, the amount of heat entering a section is equal to amount of heat coming out.[8]

Transient conduction (see Heat equation) occurs when the temperature within an object changes as a function of time. Analysis of transient systems is more complex and often calls for the application of approximation theories or numerical analysis by computer.[8]

The flow of fluid may be forced by external processes, or sometimes (in gravitational fields) by buoyancy forces caused when thermal energy expands the fluid (for example in a fire plume), thus influencing its own transfer. The latter process is often called "natural convection". All convective processes also move heat partly by diffusion, as well. Another form of convection is forced convection. In this case the fluid is forced to flow by using a pump, fan or other mechanical means.

Convective heat transfer, or convection, is the transfer of heat from one place to another by the movement of fluids, a process that is essentially the transfer of heat via mass transfer. Bulk motion of fluid enhances heat transfer in many physical situations, such as (for example) between a solid surface and the fluid.[10] Convection is usually the dominant form of heat transfer in liquids and gases. Although sometimes discussed as a third method of heat transfer, convection is usually used to describe the combined effects of heat conduction within the fluid (diffusion) and heat transference by bulk fluid flow streaming.[11] The process of transport by fluid streaming is known as advection, but pure advection is a term that is generally associated only with mass transport in fluids, such as advection of pebbles in a river. In the case of heat transfer in fluids, where transport by advection in a fluid is always also accompanied by transport via heat diffusion (also known as heat conduction) the process of heat convection is understood to refer to the sum of heat transport by advection and diffusion/conduction.

Free, or natural, convection occurs when bulk fluid motions (streams and currents) are caused by buoyancy forces that result from density variations due to variations of temperature in the fluid. Forced convection is a term used when the streams and currents in the fluid are induced by external means—such as fans, stirrers, and pumps—creating an artificially induced convection current.[12]

Convective cooling is sometimes described as Newton's law of cooling:

The rate of heat loss of a body is proportional to the temperature difference between the body and its surroundings.

However, by definition, the validity of Newton's law of Cooling requires that the rate of heat loss from convection be a linear function of ("proportional to") the temperature difference that drives heat transfer, and in convective cooling this is sometimes not the case. In general, convection is not linearly dependent on temperature gradients, and in some cases is strongly nonlinear. In these cases, Newton's law does not apply.

In a body of fluid that is heated from underneath its container, conduction and convection can be considered to compete for dominance. If heat conduction is too great, fluid moving down by convection is heated by conduction so fast that its downward movement will be stopped due to its buoyancy, while fluid moving up by convection is cooled by conduction so fast that its driving buoyancy will diminish. On the other hand, if heat conduction is very low, a large temperature gradient may be formed and convection might be very strong.

The Rayleigh number (

R
a

{\displaystyle Ra}

) is the product of the Grashof and Prandtl numbers. It is a measure which determines the relative strength of conduction and convection.[13]

The Rayleigh number can be understood as the ratio between the rate of heat transfer by convection to the rate of heat transfer by conduction; or, equivalently, the ratio between the corresponding timescales (i.e. conduction timescale divided by convection timescale), up to a numerical factor. This can be seen as follows, where all calculations are up to numerical factors depending on the geometry of the system.

The buoyancy force driving the convection is roughly

g
Δ
ρ

L

3

{\displaystyle g\Delta \rho L^{3}}

, so the corresponding pressure is roughly

g
Δ
ρ
L

{\displaystyle g\Delta \rho L}

. In steady state, this is canceled by the shear stress due to viscosity, and therefore roughly equals

μ
V

/

L
=
μ

/

T

c
o
n
v

{\displaystyle \mu V/L=\mu /T_{conv}}

, where V is the typical fluid velocity due to convection and

T

c
o
n
v

{\displaystyle T_{conv}}

 the order of its timescale.[citation needed] The conduction timescale, on the other hand, is of the order of

T

c
o
n
d

=

L

2

/

α

{\displaystyle T_{cond}=L^{2}/\alpha }

.

Convection occurs when the Rayleigh number is above 1,000â€“2,000.

Thermal radiation is energy emitted by matter as electromagnetic waves, due to the pool of thermal energy in all matter with a temperature above absolute zero. Thermal radiation propagates without the presence of matter through the vacuum of space.[14]

Thermal radiation is a direct result of the random movements of atoms and molecules in matter. Since these atoms and molecules are composed of charged particles (protons and electrons), their movement results in the emission of electromagnetic radiation, which carries energy away from the surface.

The Stefan-Boltzmann equation, which describes the rate of transfer of radiant energy, is as follows for an object in a vacuumÂ :

For radiative transfer between two objects, the equation is as follows:

where Q is the heat flux, ε is the emissivity (unity for a black body), σ is the Stefan–Boltzmann constant, and T is the absolute temperature (in kelvins or degrees Rankine). Radiation is typically only important for very hot objects, or for objects with a large temperature difference.

Radiation from the sun, or solar radiation, can be harvested for heat and power.[15] Unlike conductive and convective forms of heat transfer, thermal radiation can be concentrated in a small spot by using reflecting mirrors, which is exploited in concentrating solar power generation.[16] For example, the sunlight reflected from mirrors heats the PS10 solar power tower and during the day it can heat water to 285 °C (545 °F).[citation needed]

Phase transition or phase change, takes place in a thermodynamic system from one phase or state of matter to another one by heat transfer. Phase change examples are the melting of ice or the boiling of water. The Mason equation explains the growth of a water droplet based on the effects of heat transport on evaporation and condensation.

Phase transitions involve the four fundamental states of matter:

The boiling point of a substance is the temperature at which the vapor pressure of the liquid equals the pressure surrounding the liquid[18][19] and the liquid evaporates resulting in an abrupt change in vapor volume.

Saturation temperature means boiling point. The saturation temperature is the temperature for a corresponding saturation pressure at which a liquid boils into its vapor phase. The liquid can be said to be saturated with thermal energy. Any addition of thermal energy results in a phase transition.

At standard atmospheric pressure and low temperatures, no boiling occurs and the heat transfer rate is controlled by the usual single-phase mechanisms. As the surface temperature is increased, local boiling occurs and vapor bubbles nucleate, grow into the surrounding cooler fluid, and collapse. This is sub-cooled nucleate boiling, and is a very efficient heat transfer mechanism. At high bubble generation rates, the bubbles begin to interfere and the heat flux no longer increases rapidly with surface temperature (this is the departure from nucleate boiling, or DNB).

At similar standard atmospheric pressure and high temperatures, the hydrodynamically-quieter regime of film boiling is reached. Heat fluxes across the stable vapor layers are low, but rise slowly with temperature. Any contact between fluid and the surface that may be seen probably leads to the extremely rapid nucleation of a fresh vapor layer ("spontaneous nucleation"). At higher temperatures still, a maximum in the heat flux is reached (the critical heat flux, or CHF).

The Leidenfrost Effect demonstrates how nucleate boiling slows heat transfer due to gas bubbles on the heater's surface. As mentioned, gas-phase thermal conductivity is much lower than liquid-phase thermal conductivity, so the outcome is a kind of "gas thermal barrier".

Condensation occurs when a vapor is cooled and changes its phase to a liquid. During condensation, the latent heat of vaporization must be released. The amount of the heat is the same as that absorbed during vaporization at the same fluid pressure.[20]

There are several types of condensation:

Melting is a thermal process that results in the phase transition of a substance from a solid to a liquid. The internal energy of a substance is increased, typically with heat or pressure, resulting in a rise of its temperature to the melting point, at which the ordering of ionic or molecular entities in the solid breaks down to a less ordered state and the solid liquefies. Molten substances generally have reduced viscosity with elevated temperature; an exception to this maxim is the element sulfur, whose viscosity increases to a point due to polymerization and then decreases with higher temperatures in its molten state.[21]

Heat transfer can be modeled in the following ways.

Climate models study the radiant heat transfer by using quantitative methods to simulate the interactions of the atmosphere, oceans, land surface, and ice.

The heat equation is an important partial differential equation that describes the distribution of heat (or variation in temperature) in a given region over time. In some cases, exact solutions of the equation are available;[22] in other cases the equation must be solved numerically using computational methods.

Lumped system analysis often reduces the complexity of the equations to one first-order linear differential equation, in which case heating and cooling are described by a simple exponential solution, often referred to as Newton's law of cooling.

System analysis by the lumped capacitance model is a common approximation in transient conduction that may be used whenever heat conduction within an object is much faster than heat conduction across the boundary of the object. This is a method of approximation that reduces one aspect of the transient conduction system—that within the object—to an equivalent steady state system. That is, the method assumes that the temperature within the object is completely uniform, although its value may be changing in time.

In this method, the ratio of the conductive heat resistance within the object to the convective heat transfer resistance across the object's boundary, known as the Biot number, is calculated. For small Biot numbers, the approximation of spatially uniform temperature within the object can be used: it can be presumed that heat transferred into the object has time to uniformly distribute itself, due to the lower resistance to doing so, as compared with the resistance to heat entering the object.[23]

Heat transfer has broad application to the functioning of numerous devices and systems. Heat-transfer principles may be used to preserve, increase, or decrease temperature in a wide variety of circumstances.[citation needed] Heat transfer methods are used in numerous disciplines, such as automotive engineering, thermal management of electronic devices and systems, climate control, insulation, materials processing, and power station engineering.

Thermal insulators are materials specifically designed to reduce the flow of heat by limiting conduction, convection, or both. Thermal resistance is a heat property and the measurement by which an object or material resists to heat flow (heat per time unit or thermal resistance) to temperature difference.

Radiance or spectral radiance are measures of the quantity of radiation that passes through or is emitted. Radiant barriers are materials that reflect radiation, and therefore reduce the flow of heat from radiation sources. Good insulators are not necessarily good radiant barriers, and vice versa. Metal, for instance, is an excellent reflector and a poor insulator.

The effectiveness of a radiant barrier is indicated by its reflectivity, which is the fraction of radiation reflected. A material with a high reflectivity (at a given wavelength) has a low emissivity (at that same wavelength), and vice versa. At any specific wavelength, reflectivity=1 - emissivity. An ideal radiant barrier would have a reflectivity of 1, and would therefore reflect 100 percent of incoming radiation. Vacuum flasks, or Dewars, are silvered to approach this ideal. In the vacuum of space, satellites use multi-layer insulation, which consists of many layers of aluminized (shiny) Mylar to greatly reduce radiation heat transfer and control satellite temperature.[citation needed]

A heat engine is a system that performs the conversion of a flow of thermal energy (heat) to mechanical energy to perform mechanical work.[24][25]

A thermocouple is a temperature-measuring device and widely used type of temperature sensor for measurement and control, and can also be used to convert heat into electric power.

A thermoelectric cooler is a solid state electronic device that pumps (transfers) heat from one side of the device to the other when electric current is passed through it. It is based on the Peltier effect.

A thermal diode or thermal rectifier is a device that causes heat to flow preferentially in one direction.

A heat exchanger is used for more efficient heat transfer or to dissipate heat. Heat exchangers are widely used in refrigeration, air conditioning, space heating, power generation, and chemical processing. One common example of a heat exchanger is a car's radiator, in which the hot coolant fluid is cooled by the flow of air over the radiator's surface.[citation needed]

A heat sink is a component that transfers heat generated within a solid material to a fluid medium, such as air or a liquid. Examples of heat sinks are the heat exchangers used in refrigeration and air conditioning systems or the radiator in a car. A heat pipe is another heat-transfer device that combines thermal conductivity and phase transition to efficiently transfer heat between two solid interfaces.

Efficient energy use is the goal to reduce the amount of energy required in heating or cooling. In architecture, condensation and air currents can cause cosmetic or structural damage. An energy audit can help to assess the implementation of recommended corrective procedures. For instance, insulation improvements, air sealing of structural leaks or the addition of energy-efficient windows and doors.[26]

Climate engineering consists of carbon dioxide removal and solar radiation management. Since the amount of carbon dioxide determines the radiative balance of Earth atmosphere, carbon dioxide removal techniques can be applied to reduce the radiative forcing. Solar radiation management is the attempt to absorb less solar radiation to offset the effects of greenhouse gases.

The greenhouse effect is a process by which thermal radiation from a planetary surface is absorbed by atmospheric greenhouse gases, and is re-radiated in all directions. Since part of this re-radiation is back towards the surface and the lower atmosphere, it results in an elevation of the average surface temperature above what it would be in the absence of the gases.

The principles of heat transfer in engineering systems can be applied to the human body in order to determine how the body transfers heat. Heat is produced in the body by the continuous metabolism of nutrients which provides energy for the systems of the body.[27] The human body must maintain a consistent internal temperature in order to maintain healthy bodily functions. Therefore, excess heat must be dissipated from the body to keep it from overheating. When a person engages in elevated levels of physical activity, the body requires additional fuel which increases the metabolic rate and the rate of heat production. The body must then use additional methods to remove the additional heat produced in order to keep the internal temperature at a healthy level.

Heat transfer by convection is driven by the movement of fluids over the surface of the body. This convective fluid can be either a liquid or a gas. For heat transfer from the outer surface of the body, the convection mechanism is dependent on the surface area of the body, the velocity of the air, and the temperature gradient between the surface of the skin and the ambient air.[28] The normal temperature of the body is approximately 37 °C. Heat transfer occurs more readily when the temperature of the surroundings is significantly less than the normal body temperature. This concept explains why a person feels “cold” when not enough covering is worn when exposed to a cold environment. Clothing can be considered an insulator which provides thermal resistance to heat flow over the covered portion of the body.[29] This thermal resistance causes the temperature on the surface of the clothing to be less than the temperature on the surface of the skin. This smaller temperature gradient between the surface temperature and the ambient temperature will cause a lower rate of heat transfer than if the skin were not covered.

In order to ensure that one portion of the body is not significantly hotter than another portion, heat must be distributed evenly through the bodily tissues. Blood flowing through blood vessels acts as a convective fluid and helps to prevent any buildup of excess heat inside the tissues of the body. This flow of blood through the vessels can be modeled as pipe flow in an engineering system. The heat carried by the blood is determined by the temperature of the surrounding tissue, the diameter of the blood vessel, the thickness of the fluid, velocity of the flow, and the heat transfer coefficient of the blood. The velocity, blood vessel diameter, and the fluid thickness can all be related with the Reynolds Number, a dimensionless number used in fluid mechanics to characterize the flow of fluids.

Latent heat loss, also known as evaporative heat loss, accounts for a large fraction of heat loss from the body. When the core temperature of the body increases, the body triggers sweat glands in the skin to bring additional moisture to the surface of the skin. The liquid is then transformed into vapor which removes heat from the surface of the body.[30] The rate of evaporation heat loss is directly related to the vapor pressure at the skin surface and the amount of moisture present on the skin.[28] Therefore, the maximum of heat transfer will occur when the skin is completely wet. The body continuously loses water by evaporation but the most significant amount of heat loss occurs during periods of increased physical activity.

Evaporative cooling happens when water vapor is added to the surrounding air. The energy needed to evaporate the water is taken from the air in the form of sensible heat and converted into latent heat, while the air remains at a constant enthalpy. Latent heat describes the amount of heat that is needed to evaporate the liquid; this heat comes from the liquid itself and the surrounding gas and surfaces. The greater the difference between the two temperatures, the greater the evaporative cooling effect. When the temperatures are the same, no net evaporation of water in air occurs; thus, there is no cooling effect.

In quantum physics, laser cooling is used to achieve temperatures of near absolute zero (−273.15 °C, −459.67 °F) of atomic and molecular samples to observe unique quantum effects that can only occur at this heat level.

Magnetic evaporative cooling is a process for lowering the temperature of a group of atoms, after pre-cooled by methods such as laser cooling. Magnetic refrigeration cools below 0.3K, by making use of the magnetocaloric effect.

Radiative cooling is the process by which a body loses heat by radiation. Outgoing energy is an important effect in the Earth's energy budget. In the case of the Earth-atmosphere system, it refers to the process by which long-wave (infrared) radiation is emitted to balance the absorption of short-wave (visible) energy from the Sun. Convective transport of heat and evaporative transport of latent heat both remove heat from the surface and redistribute it in the atmosphere.

Thermal energy storage includes technologies for collecting and storing energy for later use. It may be employed to balance energy demand between day and nighttime. The thermal reservoir may be maintained at a temperature above or below that of the ambient environment. Applications include space heating, domestic or process hot water systems, or generating electricity.