What a great idea!

A little-known fact is that Galileo observed Neptune in 1633 while studying Jupiter, 233 years before the planet was actually discovered in 1846. He thought it was a background star. A 2009 study even suggests that Galileo was well-aware of Neptune's movement and therefore could be credited as the discoverer of the 8th planet.

This paper has some of Galileo's sketches of Jupiter and Neptune, you might be able to use these in your gallery.