Why the seasons are so long
Summers of a decade, winters as long or longer, keeping to no calendar a mortal can read — what the chronicle holds, what the maesters guess, and what only the maker knows.
What the chronicle holds
Seasons are counted in years, not months.
A summer may run the better part of a decade; a winter as long, or longer. Their coming and going keeps to no calendar a mortal can read, and no maester has ever foretold the length of a season before it ended.
The Citadel keeps the count, and the white ravens carry word.
It falls to the maesters of Oldtown to declare when a season has truly turned. When it does, they loose the great white ravens — larger and cleverer than the common black birds — to carry the tidings to every keep in the realm.
The long summer of the opening years was the longest in living memory.
The chronicle's own tale begins in the last light of a summer that had run close upon ten years — the longest any man then living could recall. The old and the wise took no joy in it, for the smallfolk say a long summer means a longer winter to follow.
Winter kills, and so the realm hoards against it.
Harvests are stored, keeps are provisioned, and the North lives always half a season ahead in its reckoning. “Winter is coming” is no idle motto but a Stark's plainest statement of fact.
The maesters' theories
The maesters measure the days, and find no clockwork
Maester Nicol's labours, the Citadel holds, show that the length of the day and the count of days in a year hold steady even as the seasons wander — proof, to the learned, that the cause is not the ordinary turning of the world about its sun. What the cause is, the honest among them confess they cannot say.
SourcesTWOIAFThe septons say sin and virtue
The Faith teaches that the Father Above sends fair seasons and foul as reward and chastisement for the deeds of men — a doctrine that explains everything and predicts nothing, as doctrines of its kind tend to.
SourcesTWOIAFThe oldest tales blame sorcery
The children of the forest and the songs of the First Men bind the great winters to magic and to the Long Night that once nearly ended the world. The chronicle sets these down as legend, and notes only that the North has never entirely stopped believing them.
SourcesAGOTTWOIAF
Beyond the page
Outside the tale, the author has said plainly that the broken seasons are a matter of magic, not of any orbit or astronomy that could be worked out on parchment — and that the true answer is a mystery he means to unfold only at the very end of his story. The chronicle records this as the maker's word about his world, not as anything a maester of the Citadel could ever have discovered; within the tale, the riddle stands unsolved.
How the calendar is kept
The moon's turn
A month, reckoned by the moon — a woman is said to “flower” and a plan to ripen “in a turn or two.”
The name day
The anniversary of one's birth. A child of ten is “ten namedays old”; a nameday is marked, and sometimes feasted, much as we keep a birthday.
After the Conquest
The maesters number the years from Aegon's Conquest, when Oldtown opened its gates and the High Septon crowned the Conqueror — dating events AC (After the Conquest) or BC (Before the Conquest). The seasons, keeping their own counsel, ignore the count entirely.
Why are the seasons so long in Game of Thrones?
Within the story, no one truly knows. The seasons of Westeros last years rather than months and keep to no fixed length; the maesters have measured the days and found the year itself steady, which tells them the cause is not the ordinary turning of the world about its sun — but what the true cause is, they confess they cannot say.
How long do winters and summers last?
Each lasts years, and their length cannot be foretold. A summer may run the better part of a decade and a winter as long or longer; the long summer at the chronicle's opening was close upon ten years, the longest in living memory. The smallfolk warn that a long summer means a longer winter to follow.
Has George R. R. Martin explained why the seasons are broken?
Outside the tale, the author has said the broken seasons are a matter of magic rather than astronomy, and that the full answer is a mystery he intends to reveal only at the very end of the story. The chronicle records this as the maker's word about his world; within the story, the riddle stands unsolved.
How do the maesters know when a season has changed?
It falls to the Citadel at Oldtown to declare a true change of season. When one comes, the maesters loose the great white ravens — larger and cleverer than the common black birds — to carry word of it to every keep in the realm.