I took a lazy approach
Blank canvas with black as background.
new layer- created stars with varying hues and sizes using brush tool
Created nebula with the following steps:
...new layer - made a feathered, random selection and then filter-render- clouds
using levels changed the amount and brightness of cloud
...repeated above two steps twice more with different colors for clouds
added earth picture
added frame
masked areas on earth to show and hide frame respectively