On this day in space! Oct. 13, 1773: Astronomer Charles Messier discovers the Whirlpool Galaxy before we ever knew it was a galaxy

Automatically curated summary from Space.com.

On October 13, 1773, French astronomer Charles Messier catalogued the Whirlpool Galaxy (M51) as a non-comet object, though he could not discern its galaxy status or spiral structure. Later observed by William Parsons as a spiral nebula, Edwin Hubble eventually confirmed M51 was a distinct galaxy. Located approximately 31 million light-years from Earth, M51 displays a prominent spiral shape. NASA scientists suspect this shape and heightened star formation were triggered by a gravitational interaction with its companion galaxy, NGC 5195, around 500 million years ago.

Context and limitations

Historical timeline details reflect the provided excerpt; the claim that NGC 5195 passed through M51's disk 500 million years ago to form its spiral structure is framed as a scientific suspicion rather than a proven fact.