currently the sun earth moon are object sphere, it will be a visual enhancement if you add textures to the 3D java view
http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=1830.msg7132#msg7132

in normal 3D, i have customized the pictures here
http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=1501.0
you can used sun, earth, moon

this can be your efforts to make the applet better for learning ;D