Imagine you want to measure the size of a room, but it's completely dark. If you shout, you can tell if the space you're in is relatively big or small, depending on how long it takes to hear the echo after it bounces off the wall.
A nebula known as "the Spider" glows fluorescent green in an infrared image from NASA's Spitzer Space Telescope and the Two Micron All Sky Survey (2MASS). The Spider, officially named IC 417, lies near a much smaller object called NGC 1931, not pictured in the image. Together, the two are called "The Spider and the Fly" nebulae. Nebulae are clouds of interstellar gas and dust where stars can form.
Scores of baby stars shrouded by dust are revealed in this infrared image of the star-forming region NGC 2174, as seen by NASAs Spitzer Space Telescope. Some of the clouds in the region resemble the face of a monkey in visible-light images, hence the nebula's nickname: the "Monkey Head."
The Spitzer Space Telescope is a NASA mission managed by the Jet Propulsion Laboratory. This website is maintained by the Spitzer Science Center, located on the campus of the California Institute of Technology and part of NASA's Infrared Processing and Analysis Center.