Bear in the Sky by Stefan Czernecki and Timothy Rhodes, illustrated by Stefan Czernecki (Hyperion, 1990).
This was a childhood favorite of mine. Judging from the little I could find online, it doesn't appear to be a well-known book, which is a shame. The folk art illustrations left a strong impression on me.
This is an origin story for the constellation Ursa Major, the Great Bear. The title bear loves to dance in the forest with the birds and other creatures. When he is shot with an arrow by hunters, a gypsy couple nurses him back to health, names him Zloty, and gives him a velvet vest. His joyful dancing cures a princess who cannot smile. However, she is a cruel princess, and keeps Zloty captive. When he will not dance for her anymore, she gets mad and throw his vest out the window, which disappears and leaves a stairway of stars. Zloty climbs the stars into the sky, where you can still see him dancing.