Well, to make your Earth rotate you could simply keyframe the rotation or you could write a simple expression to rotate it.
If you want to make the Earth rotate around its own axis as well as rotate around the sun all you have to do is group the planet to itself then move the center point for the group to match that of the sun. Keyframe (or write an expression) the rotation of the group. This will animate the Earth around the sun while the keyframe or expression that you set up for the earth itself will animate the rotation of the planet around itself. It's a very simple thing to do. What version of Maya are you using. I have 6.5 and would be willing to set up a demonstration file for you so you can download it and use it. The hardest thing to understand is grouping an object to itself. When you do this, all your really doing is giving the object a second set of attributes to play with. Each set of attributes works independently of the other. In other words; you can have more than one rotation or translation for the same object.
OK. I'll post a link to a file in about 6 to 10 hours when I get home from work. It will include the sun and earth objects plus the expression driven animation. I'll also include a brief explaination of the expression and how it works.
You want the camera to rotate on its Y axis for 20 degrees? Keyframe it.
The camera is just like any other object in the scene. I assume you're using the "pers" camera. It's the default camera that lets you move all around the scene. Anyway, choose it in the Outliner then set up your start and end keyframe.
Just so you know, I think most people would agree that it is better to create a new camera to use to shoot the scene. The default cameras are tools to let you see the scene while you're building and animating it.
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