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On this day in space! Oct. 13, 1773: Astronomer Charles Messier discovers the Whirlpool Galaxy before we ever knew it...
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On Oct. 13, 1773, French astronomer Charles Messier catalogued a fuzzy object in the northern sky that is now known as the Whirlpool Galaxy, or Messier 51. At the time, he was not searching for galaxies. He was scanning for comet-like objects that could confuse comet hunters. He recorded it as M51, the 51st non-comet entry in his catalog, without knowing its true nature.
Messier was the chief astronomer of the Marine Observatory in Paris, which was dedicated to studying comets. In 1758, while studying a comet, he stumbled across M1, also known as the Crab Nebula, his first non-comet object. Such objects looked like fuzzy blobs similar to comets but did not move like comets. By 1773, he had catalogued over four dozen of these objects to help astronomers avoid mistaking them for comets.
Messier could not see the Whirlpool Galaxy’s spiral structure, and he did not identify it as a galaxy. Seventy-two years later, another astronomer, William Parsons, observed its whirlpool shape. He thought it was a spiral nebula, not a galaxy. Eventually, Edwin Hubble determined that M51 and similar features were actually galaxies, transforming humanity’s understanding of the cosmos.
The Whirlpool Galaxy is located about 31 million light-years from Earth and is considered a textbook example of a spiral galaxy. It has a magnitude of 8.4 on the brightness scale used by astronomers. That means it can be observed through a small telescope, most easily during May, according to NASA. It appears in the constellation Canes Venatici, or the Hunting Dogs, just below the handle of the Big Dipper.
Scientists suspect the Whirlpool Galaxy gets its striking spiral shape from a close interaction with its neighbor galaxy NGC 5195. The companion may have passed through M51’s main disk about 500 million years ago, NASA Spitzer Space Telescope scientists have said. They described the event as a gravitational tug of war. The companion’s pull would compress gas and induce extra starbirth, jump-starting the process by which stars form. This interaction may also have triggered an increased level of star formation in M51.
The object’s history shows how astronomical classification evolves over time. What Messier saw as a comet impostor later became a spiral nebula, and then a galaxy. M51 also helped build the Messier catalog, which remains widely used by amateur and professional observers. Its story links the practical work of comet hunting to modern studies of galaxy structure and evolution.
Today, the Hubble Space Telescope reveals the Whirlpool Galaxy as a dazzling spiral. Amateur astronomers can still spot it under dark skies in spring. Its ongoing interaction with NGC 5195 offers a nearby laboratory for studying star formation. The discovery made on Oct. 13, 1773, remains a milestone in space history.
