On this Day in History in 1612: First observation of Neptune – Galileo observes and records a “fixed star” without realising it is a planet.
On this Day in History in 1920: Francis G. Pease’s interferometer at Mount Wilson Observatory is the first to measure the diameter of a star – the Betelgeuse.
On this Day in History in 1671: Giovanni Cassini discovers Iapetus, satellite of Saturn.
On this Day in History in 1773: The Whirlpool Galaxy was discovered by Charles Messier.
On this Day in History in 1848: Hyperion, moon of Saturn, discovered by Bond (US) & Lassell (England).
Fun Fact of the Day: The Solar System’s cosmographical boundary is defined by the outer limit of Oort Cloud. To simplify things, Sun’s gravitational dominance ends with Oort Cloud.
On this Day in History in 1789: William Herschel discovers Saturn’s moon Enceladus.
On this Day in History in 1820: Royal Astronomical Society founded in England.