The Chandra X-ray Observatory is a space telescope launched on STS-93 by NASA on July 23, 1999. Chandra is sensitive to X-ray sources 100 times fainter than any previous X-ray telescope, enabled by the high angular resolution of its mirrors. Since the Earth's atmosphere absorbs the vast majority of X-rays, they are not detectable from Earth-based telescopes, requiring a space-based telescope to make these observations. It is a Earth satellite in a 64 hour orbit, its mission is ongoing as of 2012.

Chandra Observatory is the third of NASA's four Great Observatories. The first was Hubble Space Telescope; second the Compton Gamma Ray Observatory, launched in 1991; and last is the Spitzer Space Telescope. Of those four, three continue; Compton ended in 2000. Chandra has been compared to being as revolutionary to astronomy as Galileo's first telescope.

It was named in honor of the Nobel-prize winning physicist S. Chandrasekhar who worked for University of Chicago from 1937 until he passed away in 1995. He was known for determining the maximum mass for white dwarfs. "Chandra" also means "moon" or "luminous" in Sanskrit. Before 1998, it was known as AXAF, the Advanced X-ray Astrophysics Facility. AXAF was assembled and tested by TRW (now Northrop Grumman Aerospace Systems) in Redondo Beach, California.

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