Messier 106: Spiral Galaxy in Canes Venatici

M106 is one of the brightest and largest spiral galaxies in the spring sky, lying in the faint constellation Canes Venatici just below the Big Dipper. It shows well even in small telescopes.

What it is

M106 is a big spiral galaxy, tilted so we see it at a steep angle, with a bright core and two main arms. It lies about 24 million light-years away, and its 19′ length works out to roughly 130,000 light-years. Its center holds an active supermassive black hole that makes it a Seyfert galaxy. Radio and X-ray images show two extra "anomalous arms" that do not follow the visible spiral; they are thought to be gas heated by jets from the black hole. Clouds of gas orbiting close to that black hole produce natural microwave lasers (water masers), and by tracking their motion astronomers have measured the galaxy's distance geometrically, without relying on standard candles. That makes M106 an anchor for the cosmic distance scale and for measurements of the expansion rate of the universe. For other spirals nearby, see M63 and M94.

When to see it

M106 is a spring galaxy, highest around midnight in late March and high in the evening from April into June. From about 40°N it passes nearly overhead, reaching roughly 83°. From the Southern Hemisphere it stays low in the north and is out of reach south of about 40°S.

How to find it

The simplest route uses the Big Dipper. Start at Megrez, the star where the handle joins the bowl, and go almost exactly due south about 9.7°, a bit less than the length of the bowl from Megrez to Merak. Another way: M106 lies roughly halfway between Phecda, the bowl's southeast corner star, and Chara (Beta Canum Venaticorum), about 6.5° north-northwest of Chara.

What you will see

In binoculars M106 is a fairly easy oval glow with a brighter center under dark skies, and it can still be seen from suburban sites. A 70–100 mm telescope shows an elongated haze, running north-northwest to south-southeast, with a bright, compact core. A 200 mm or larger telescope shows a large, mottled oval with a bright nucleus and, under a dark sky, hints of the arms curving off the ends of the core. Filters do not help.

History

Pierre Méchain discovered M106 in July 1781, but it was not included in Messier's published catalog. In 1947 Helen Sawyer Hogg added it to the list as M106, one of several objects from Messier's and Méchain's notes added in the 20th century to bring the catalog to 110.