This is one of my favorite Spitzer images of all: W5, a gas cloud 6000 light years away in Cassiopeia. To give you an idea of the scale, the full Moon could fit three times across this image!

What looks like a Valentine's Day heart to us is actually a gigantic cavity more than 150 light years across, carved out by the intense winds and ultraviolet light of the stars forming inside it. The fingers of material on the edges are being eroded away by those stars like sandbars in a current, and so they point right back to those stars' locations.

Original blog post
Original press release
Image credit: NASA/JPL-Caltech/Harvard-Smithsonian CfA