M51

The Whirlpool Galaxy is a grand-design spiral galaxy located about 23 million light-years away in the constellation Canes Venatici. It is one of the most famous galaxies in the sky, renowned for its clearly defined spiral arms. M51 is interacting with its smaller companion galaxy NGC 5195 (sometimes called M51b), which is connected to M51 by a tidal bridge of gas and dust. This gravitational interaction has enhanced M51's spiral structure and triggered star formation along the arms.

Located about 3.5 degrees southwest of Eta Ursae Majoris (Alkaid), the end star of the Big Dipper's handle. In binoculars, M51 appears as a fuzzy double patch (the galaxy and its companion). A 4-inch telescope at 80-100x shows two distinct fuzzy cores connected by a hazy bridge. The spiral arms require an 8-inch or larger telescope and dark skies — look with averted vision and give your eyes time to adapt. An 12-inch telescope under excellent conditions reveals the spiral structure beautifully. Best observed from March through July.

Discovered by Charles Messier on October 13, 1773. Its companion NGC 5195 was discovered by Pierre Mechain in 1781. In 1845, Lord Rosse observed M51 through his 72-inch 'Leviathan of Parsonstown' and made the first drawing showing spiral structure — the first recognition that some nebulae had spiral form. This was a landmark moment in the history of astronomy.