An ancient symbol of Venus, the Evening Star—

http://www.log24.com/log/pix10B/101007-EveningStar.jpg

For some background, see Anti-Christmas (June 25), 2008 and The Devil and Wallace Stevens.

A purely mathematical version of the same figure—

http://www.log24.com/log/pix10B/101007-KaneReflGps19.gif