Space Exploration Timeline

<see whole timeline

OSO 8 telescope

Jun 21, 1975 – Jul 8, 1986

Found an iron emission line in the X-ray spectrum of a galaxy cluster.

https://en.wikipedia.org/wiki/Orbiting_Solar_Observatory

Includes events (2):
Jun 21, 1975
Launch of OSO 8 (OSO I)
More
Jul 8, 1986
Re-entry date of OSO 8 (OSO I)
More