Sunday's Astro picture of the day was the solar spectrum -- who doesn't love the sun?
Image courtesy N. Sharp of KPNO (larger image and credit here). It's a high--resolution spectrum that's been folded many times to fit in a rectangular space. Those dark bands are absorption lines, caused by metals in the sun's atmosphere.
A cheap prism, or a piece of diffraction grating plastic, is just enough to resolve the most prominent Frauenhofer lines for yourself. Girl Scouts think that's really cool. Undergrads think it's utterly boring.
[That the image resembles a gay-pride rainbow sticker, and was posted on APOD 4 days before Stonewall Day, appears to be a coincidence.]