British astronomer William Lassell discovered Neptune’s largest moon, Triton.
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A Neptune-sized exomoon became the first one discovered outside the Solar System.
Cosmonaut Alexey Leonov made the first spacewalk when he left his Voskhod 2 spacecraft.
Radiation from an explosion on the magnetar SGR 1806-20 reached Earth.
The Apollo-Soyuz Test Project completed the world's first international space rendezvous.
A conjunction of Sun, Mercury, Venus, Mars, Jupiter, Saturn, and the Moon occurred.
