From A Wiki of Ice and Fire
- The Red Comet should not be confused with the red wanderer.
The red comet is a comet that appeared in the sky over Westeros in 298AL. It is red, with a long tail that to some appears to cover half the sky. It is visible by day and outshines the moon at night. Some believe the color of the comet is blood red. It was first spied by Jhogo just prior to the birth of Daenerys Targaryen's dragons.
Names for the Comet
There are as many names as there are interpretations for this ominous heavenly body.
- In King's Landing is goes by "King Joffrey's Comet" at court and the "Red Messenger" or “Dragon’s Tail” in the streets.
- It is also called the "Red Messenger" by the soldiers in the Riverlands.
- Among the Faith it is known as the "Sword that Slays the Season."
- Among the Night's Watch, it is known as "Mormont's Torch".
- The comet's Dothraki name is "shierak qiya", meaning "bleeding star".
- Gendry names it the "Red Sword" on account of its sword-like shape. 
- When Daenerys is taking a bath in Qarth she names it the Bleeding Star.
Meanings of the Comet
Among the peoples of Westeros and abroad, the comet takes on different meanings. To some, like Melisandre and Old Nan, it signals the coming of dragons.  Old Nan claimed to be able to smell the comet. To others it hails future triumph and ascent to a throne for Joffrey and Daenerys and simply future triumph for Edmure Tully. 
To many more, such as Brynden Tully, Aeron Greyjoy and Osha it signifies the onset of war and the bloodshed that comes with it. Some, like Greatjon Umber look upon the comet as a symbol of vengeance.
To Daenerys Targaryen - who first sees it on the night she had burned Khal Drogo, the night her dragons had awakened - it is a herald of her coming, a sign meant for her to follow, which she does through the Red Waste. The comet slowly fades as Daenerys takes to sea from her final stop at Qarth and in one vision in the House of the Undying the Undying Ones claim to have sent the comet to guide Daenerys to them. .
A Game of Thrones
As Daenerys Targaryen's khalasar waits for night falls before Khal Drogo’s funeral pyre, it is Jhogo that first notices the red comet; it is the first star of the evening. It is said that the more fiercely a man burned in life, the brighter his star. Daenerys uses this as a sign to light the pyre.  However, the red comet is first mentioned a little earlier in the book, but obviously at the same time, when Maester Luwin is studying it through his Myrish lens tube, the morning of the day when a raven brings the news of Eddard Stark's death in Winterfell.
A Clash of Kings
Arya Stark is journeying north with Yoren and his recruits for the Wall disguised as Arry. She lies and looks up at the comet which she thinks is both splendid and scary comet. Gendry, the smith called it The Red Sword, saying it looked a sword, the blade still red-hot from the forge. She can see the sword but to her it looks like her father’s great sword Ice, covered in blood as it had been after her father’s head was cut off.
On Joffrey’s name day Sansa can see the long tail of the red comet from her tower window. When Ser Arys Oakheart arrives to escort her to the tourney grounds, she asks him what it means. He states that it means glory to King Joffrey. The gods have raised it as a banner in his honor. The small folk have named it King Joffrey’s comet. Sansa is not so sure and replies that she had heard the servants call it the Dragon’s Tail. To this Ser Arys states that Joffrey sits in the dragon’s throne and the House Lannister color is crimson. Sansa wonders, with foreboding, if it is true and thinks that if Joffrey is a Baratheon, it should be a gold comet.
Tyrion returns to the Broken Anvil after breaking the news to Cersei that he is acting Hand of the King to find Varys there with Shae, much to his dismay. After some veiled threats between them, Varys asks if Tyrion has seen the Red Comet, and Tyrion replies he is not blind; on the Kingsroad it had seemed to cover half the sky. Varys tells Tyrion that on the streets it is called the Red Messenger.
|“||“They say it comes as a herald before a king, to warn of fire and blood to follow.” ||”|
|“||“Blood and fire, boy, and nothing sweet.”||”|
Septon Chayle says “It is the sword that slays the season,” which seems to make sense to Bran since a White raven had brought word of Autumn. Old Nan tells him the comet foretells of dragons. She could not see the comet, being blind, but claims she can smell it. The direwolves are howling.
Catelyn enters the room where her dying father, Hoster Tully, is sleeping to find her uncle, Brynden Tully. She asks about the scouting reports, and her uncle asks her outside to avoid waking her father. He tells her that the men call the Red Comet the Red Messenger, but wonders what the message is. Catelyn states “The Greatjon told Robb that the old gods have unfurled a red flag of vengeance for Ned. Edmure thinks it’s an omen of victory for Riverrun, he sees a fish with a long tail, in the Tully colors, red against blue.” Catelyn knows crimson is the Lannister color. Brynden states “That thing’s not crimson, nor Tully red, the mud red of the river. That’s blood up there, child, smeared across the sky.’’ Catelyn asks whose blood.
As Theon sails towards his father’s castle at Pyke he can see the Red Comet, which he considers his comet. Later, when Theon is met by is uncle Aeron Greyjoy, he tells his uncle that in Riverrun they say:
|“||…the Red Comet is a herald of a new age. A messenger from the gods.||”|
To this Aeron states it is a sign from the Drowned God, not their gods:
|“||A burning brand it is, such as our people carried of old. It is the flame the Drowned God brought from the sea, and it proclaims a rising tide. It is time to hoist our sails and go forth into the world with fire and sword, as he did.||”|
Daenerys Targaryen is having her small khalasar follow the Red Comet the Dothraki name shierak qiya (Bleeding Star). The old men mutter that it is an ill omen, but it appeared the night they cremated Khal Drogo and her dragons awakened; she considers it the herald of her coming. She is told by Doreah that it is grim in that direction, but she really has no choice with khalasar of Khal Pono or Khal Jhaqo and others to the north; their hundred people with only four warriors would be no match. Nor could they withstand the peaceful Lamb Men to the south, who had no love for her. The only way seems to be into the red lands, and when she tells her people they will follow comet, no words against it are raised.
Tyrion Lannister had visited the Guildhall of the Alchemists about the preparation of the Wildfire, and then met with Ser Cleos Frey about Robb Stark’s terms for peace when he is returning to the Red Keep. There is a crowd listening to a prophet when the litter passes through Cobbler's Square. The prophet is talking about corruption as the Red Comet is directly behind the prophet over the castle of Aegon's high hill. The prophet calls the comet the Father’s scourge. He proclaims:
|“||We have become swollen, bloated, foul. Brother couples with sister in the bed of kings, and the fruit of their incest capers in his palace to the piping of a twisted little monkey demon. Highborn ladies fornicate with fools and give birth to monsters! Even the High Septon has forgotten the gods! He bathes in scented waters and grows fat on lark and lamprey while his people starve! Pride comes before prayer, maggots rule our castles, and gold is all... but no more! The Rotten Summer is at an end, and the Whoremonger King is brought low! When the boar did open him, a great stench rose to heaven and a thousand snakes slid forth from his belly, hissing and biting!” He jabbed his bony finger back at comet and castle. “There comes the Harbinger! Cleanse yourselves, the gods cry out, lest ye be cleansed! Bathe in the wine of righteousness, or you shall be bathed in fire! Fire!||”|
There are shouts of “Fire!” but shouts of derision almost drown those shouts out.
After her khalisar’s arrival in Qarth, Daenerys is taking a bath and wondering how she will conquer the Seven Kingdoms with her meager khalisar. She takes comfort in thinking that the Bleeding Star had led her to Qarth for a purpose, and if the gods intend for her to conquer they will send a sign. 
|“||Dragons . . . it be dragons, boy.||”|
|“||We follow the comet.||”|
References and Notes
- ↑ 1.0 1.1 A Clash of Kings, Prologue.
- ↑ 2.0 2.1 A Clash of Kings, Chapter 3, Tyrion.
- ↑ 3.0 3.1 3.2 3.3 3.4 3.5 A Clash of Kings, Chapter 7, Catelyn.
- ↑ 4.0 4.1 A Game of Thrones, Chapter 72, Daenerys.
- ↑ 5.0 5.1 5.2 A Clash of Kings, Chapter 2, Sansa.
- ↑ 6.0 6.1 6.2 6.3 6.4 A Clash of Kings, Chapter 4, Bran.
- ↑ A Clash of Kings, Chapter 5, Arya.
- ↑ 8.0 8.1 8.2 A Clash of Kings, Chapter 12, Daenerys.
- ↑ 9.0 9.1 A Clash of Kings, Chapter 1, Arya.
- ↑ 10.0 10.1 A Clash of Kings, Chapter 27, Daenerys.
- ↑ 11.0 11.1 A Clash of Kings, Chapter 11, Theon.
- ↑ A Clash of Kings, Chapter 48, Daenerys.
- ↑ A Game of Thrones, Chapter 66, Bran.
- ↑ A Clash of Kings, Chapter 20, Tyrion.