In Norse mythology, Arvak ("early-riser") was one of the horses (with Alsvid) that pulled Sol's chariot (i.e. the sun). The horses' mane gave off the light; the sun itself gave off the heat.
In Norse mythology, Sol (also Sunna, Sunne and Frau Sunne -- derivation of the words sun and Sunday) was the goddess of the sun (called Alfrodull meaning "glory of elves"), a daughter of Mundilfari and Glaur, and wife of Glen.
She was chased during the day by Skoll, a wolf that wanted to devour her.
The earth was protected fom the full heat of the sun by Svalin, who stood between the earth and Sol.