Thiazi’s eyes: a giant’s eyes among the stars
Thiazi is a giant in Norse myth who is killed by the gods. In Snorri’s Skáldskaparmál, written around 1220, his daughter Skaði arms herself and goes to Ásgard to avenge him. The gods offer her a settlement instead: she may choose a husband from among them, though only by looking at their feet, and they must make her laugh, which Loki manages in an undignified way. Snorri then adds: ‘Odin did this by way of atonement to Skadi: he took Thjazi’s eyes and cast them up into the heavens, and made of them two stars.’
Odin or Thor?
The Poetic Edda has the same deed, but a different god. In Hárbarðsljóð, a quarrel in verse between Thor and a ferryman, Thor boasts: ‘Thjazi I felled ... and I hurled the eyes of Alvaldi’s son to the heavens hot above; of my deeds the mightiest marks are these, that all men since can see.’
So the two sources disagree about who threw the eyes. Snorri names Odin, the poem gives the honour to Thor. What both agree on is the point of the story: the stars are a mark of a deed, put up where anyone can see them.
Which stars?
Neither text says. Henry Adams Bellows, who translated the poem in 1923, put it plainly: ‘It is not known which stars were called Thjazi’s Eyes.’ No medieval source names them.
The usual answer, Castor and Pollux in Gemini, is a 19th-century guess. Jacob Grimm, writing in 1835, looked for two stars standing close together and equal in brightness and size, and wrote ‘perhaps the Twins?’, question mark included. The Icelandic-English Dictionary of Cleasby and Vigfússon repeated it in 1874 as ‘Castor and Pollux (?)’, again with the question mark. Later books often drop the question mark. We keep it, because it is the honest part of the answer.
Looking for them yourself
If you would like to see the pair the guess points to, Castor and Pollux are two bright stars side by side in Gemini, easy to find on winter evenings north of the equator. They fit Grimm’s description well. Whether anyone in the Norse world looked at them and thought of Thiazi, nobody knows.