French astronomer Charles Messier discovered the Whirlpool Galaxy (pictured), an interacting, grand design spiral galaxy located an estimated 31 million light-years away.

Charles Messier was a French astronomer. He published an astronomical catalogue consisting of 110 nebulae and star clusters, which came to be known as the Messier objects, referred to with the letter M and their number between 1 and 110. Messier's purpose for the catalogue was to help astronomical observers distinguish between permanent and transient visually diffuse objects in the sky.

The Whirlpool Galaxy, also known as Messier 51a (M51a) or NGC 5194, is an interacting grand-design spiral galaxy with a Seyfert 2 active galactic nucleus. It lies in the constellation Canes Venatici, and was the first galaxy to be classified as a spiral galaxy. It is 31 million lightyears away and 23.58 kiloparsecs (76,900 ly) in diameter.

Interacting galaxies are galaxies whose gravitational fields result in a disturbance of one another. Major mergers occur between galaxies with similar amounts of mass, whereas minor mergers involve galaxies with masses that vary significantly. An example of a minor interaction is a satellite galaxy disturbing the primary galaxy's spiral arms. An example of a major interaction is a galactic collision, which may lead to a galaxy merger.

A grand design spiral galaxy is a spiral galaxy with prominent and well-defined continuous spiral arms, as opposed to multi-arm, patchy and flocculent spirals which have subtler structural features. The spiral arms of a grand design galaxy extend clearly around the galaxy, covering a significant portion of the galaxy's circumference. These spiral arms host much star formation, making them home to an abundance of bright, hot, and short-lived massive stars.