I'm jumping in a little late on this one . . .
To obtain constant angular velocity, set the Continuity to 0 for all rotate
keys for the object.
As for your mapping, is your texture slider up over 50 so the map is visible?
BTW: make sure your Earth is rotating counterclockwise from the top. Some of
the first Universal Pictures tag screens had it going the wrong way. They
really took some flak about that until they fixed it.
— James —