They are begrudgingly welcomed by Zorya Vechernayaya (Cloris Leachman) and Zorya Utrennyaya (Martha Kelly) – but not by the third sister, Zorya Polunochnaya (Erika Kaar), who is asleep and is strictly not to be disturbed.
The thing is, you won't often find the Zorya sisters in the same room, and it's not because they hate each other. Far from it. The problem is that the guardian goddesses must guard the skies in a never-ending relay through night and day, so their sleep cycles are out of whack.
Who are the Zorya sisters?
In Slavic mythology, the Zorya (or Zorja) are actually two guardian goddesses, the Morning Star (Utrennyaya, associated with Venus) and the Evening Star (Vechernayaya, associated with Mercury). American Gods author Neil Gaiman has swelled their number to three for dramatic effect, adding in a Midnight Star (Polunochnaya).
The Zoryas guard and watch the skies, keeping an eye on the winged doomsday hound called Simargl, who is chained to the star Polaris in the Ursa Minor constellation. But if the chain ever breaks, Simargl will devour the constellation and bring an end to the entire universe.
This is why Zorya Polunochnaya tells Shadow she must keep constant watch over the sky with her telescope, in case something terrible escapes.
The Zorya sisters serve the sun god Dažbog, who in some folk tales is actually their father. The Morning Star opens the gates to his palace every morning for the sun-chariot's departure, and at dusk the Evening Star closes the palace gates after he returns.
Are they really virgin goddesses?
When Shadow Moon climbs the non-existent fire escape to the roof of that Chicago tower block and finds the beautiful Zorya Polunochnaya keeping watch with her telescope, she asks him for a kiss – and tells him she is a virgin.
In some versions of the myth, the Zoryas are married to the moon god Myesyats, and are mothers to all of the stars in the skies. But other versions of the tale assert that the Zoryas are virgin goddesses, destined for a chaste existence.
American Gods is available on Amazon Prime Video in the UK, with new episodes available every week. Episodes air on US channel Starz on Sunday nights.