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December 12, 2020

The first confirmed black hole sits near the center of the Summer Triangle — a pattern of three bright stars that’s in the west on December evenings. Cygnus X-1 was discovered during a short rocket flight in 1964. But strong evidence of its nature was provided by a later mission. Called Uhuru, it was launched 50 years ago today.

The craft was designed to study X-rays. They’re produced by some of the hottest and brightest objects in the universe. But Earth’s atmosphere absorbs X-rays, so we can’t see them from the ground. The only way to study them is from space.

Uhuru was the first X-ray space telescope. It originally was known by a couple of other names. But it was launched by Italy from a platform off the coast of Kenya. In honor of the host country, it was renamed Uhuru — Swahili for “freedom.”

Besides its international pedigree, it had a couple of other distinctions. It was the first science satellite managed by a woman — Marjorie Townsend, an engineer at Goddard Space Flight Center. And its top scientist, Riccardo Giacconi, later won the Nobel Prize for this and other X-ray missions.

Uhuru cataloged four times the number of X-ray sources known before its mission. The list included the remnants of exploded stars, hot binary stars, galaxy clusters, and the disks around black holes. The craft took a close look at several of those targets — including Cygnus X-1, the first confirmed black hole.

Script by Damond Benningfield

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