What was this triangle I saw in space?

A few years ago I was looking through some binoculars to look at the stars. Even just with those, you can see lots of stars you cannot see with the naked eye. I saw a triangle traveling in a straight line. I don't think it was an airplane because it must have been so far up there, you wouldn't have been able to see it with the naked eye if it appeared so tiny through the binoculars. And I don't think satellites have any kind of rectangle shape so what do you think it may have been?