Step 1: DRAWING THE MOON!
Note: To draw a perfect circle, press shift while selecting.
Hit "x" key to change foreground to background color and set foreground color to #F0FAFF. Then fill selection on the current new layer with this color. To draw the moon's surface, select Filter > Artistic > Sponge and adjust the following settings to the image
Note: You can set your own values if you chose diferent sizes. Moreover you should try to set your own values because with this filter you may get different results with the same values. Just try to reapply this filter until you get the proper result. After applying this filter you can Undo [Ctrl+Z] this action and then press [Ctrl+F] to select last used filter once again.