Follow these tutorials.
The least two are by Greg Martin.
Post your when you done ;D.
http://blog.hexagonstar.com/galaxy-tutorial/
http://gallery.artofgregmartin.com/tuts_arts/making_a_star_field.html
http://gallery.artofgregmartin.com/tuts_arts/making_a_planet.html
blah blah blah:o
how can we use this in Universe Sandbox? ???
blah blah blah