description EXOSAT Overview
EXOSAT was a European Space Agency space observatory launched in 1983 to study X-ray sources beyond Earth. Operating until 1986, it observed objects within and outside the Milky Way, including compact stars, binary systems, active galactic nuclei, and other variable high-energy sources. Its highly eccentric orbit permitted unusually long, uninterrupted observations, making the mission particularly useful for examining how the X-ray brightness of astronomical objects changed over time.
help EXOSAT FAQ
What was EXOSAT, and when did it operate?
EXOSAT was ESA's European X-ray Observatory Satellite, launched on May 26, 1983. It made observations until April 1986 and re-entered Earth's atmosphere on May 6, 1986, according to the [ESA mission overview](https://www.esa.int/Science_Exploration/Space_Science/Exosat_overview).
What did EXOSAT observe?
It studied high-energy sources including active galactic nuclei, X-ray binary systems, supernova remnants, and galaxy clusters. These targets let astronomers examine compact stars, accretion, and violent processes outside visible light.
How did EXOSAT's orbit help its observations?
Its highly elliptical orbit let the instruments operate for up to 76 hours in each revolution. That long uninterrupted observing time was one of EXOSAT's major practical advantages.
Why is EXOSAT important in the history of X-ray astronomy?
EXOSAT was the first ESA mission devoted entirely to studying the universe at X-ray wavelengths. ESA credits it with work on quasi-periodic oscillations in low-mass X-ray binaries and X-ray pulsars, and identifies it as a forerunner of XMM-Newton and NASA's Chandra.
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