Themes

So I am having this party that has about 150 guests or less. So I wanted to have a theme that would be formal and elegant. I cant have a mardi gras or a masquerade because those revolved around the homecomings that I am planning. I was thinking about like "A Star" sord of theme. Something like that because when I am going to get pictures taken outside in the nights sky. So any one has any schedules.