On This Day in Space: Charles Messier Discovered the Whirlpool Galaxy in 1773

On October 13, 1773, French astronomer Charles Messier recorded what is now known as the Whirlpool Galaxy, or Messier 51 (M51), during his systematic search for celestial bodies that could be mistaken for comets. At the time of its discovery, the object was designated as the 51st entry in Messier’s famous catalog of non-cometary objects.

Messier, who served as chief astronomer at the Marine Observatory in Paris, had begun compiling the catalog in 1758 after finding the Crab Nebula while tracking a comet. His goal was to help fellow astronomers avoid confusing stationary, fuzzy blobs with moving comets. When he first observed M51, his instruments were insufficient to reveal the galaxy’s spiral structure, and the concept of “galaxies” existing beyond the Milky Way had not yet been established.

It was not until 72 years later that astronomer William Parsons observed the distinct whirlpool shape, classifying it as a spiral nebula. The realization that such objects were actually independent star systems came decades later, thanks to Edwin Hubble.

Today, the Whirlpool Galaxy is recognized as a textbook example of a spiral galaxy, located approximately 31 million light-years from Earth. NASA notes that its striking spiral arms are likely the result of a gravitational interaction with its neighbor, NGC 5195. Scientists suggest that NGC 5195 may have passed through M51’s disk roughly 500 million years ago, an event that compressed gas and triggered intense star formation.

With a magnitude of 8.4, the galaxy is visible through small telescopes, particularly during May in the constellation Canes Venatici, located just below the handle of the Big Dipper. Modern imagery from the Hubble Space Telescope has captured the galaxy’s long lanes of stars and dust in detail, showcasing the smaller companion galaxy NGC 5195 to the right, which is actually more distant than M51 despite its apparent proximity in images.