Why should we go to the expense of launching satellites in order to gather spectral data that we could obtain from earth-based telescopes? Because, unfortunately, the earth's atmosphere does not allow light of all wavelengths to pass through it. In fact, the atmosphere will only allow visible light and some long-wavelength radio waves to pass through it. In order to see gamma, X ray, ultraviolet (UV), infrared, and microwave radiation from space, we must place telescopes and other light-gathering instruments above the atmosphere. Each satellite observes a special part of the electromagnetic spectrum. The Gamma Ray Observatory (GRO) is designed to examine the gamma ray emitters such as pulsars. The Advanced X-Ray Astrophysics Facility (AXAF) observes X ray sources such as our sun and supernovas. The Hubble Space Telescope can make observations in the infrared, visible, and ultraviolet regions of the electromagnetic spectrum. The Hubble has returned some stunning visible images from space which can be seen on its homepage. The Space Infrared Telescope Facility (SIRTF) examines the entire infrared region of the spectrum. Caption: These two images were taken by the Hubble Space Telescope. The top image is of the Orion Nebula; the lower image is the clearest image of Mars yet taken.   ©1997 The Exploratorium