Messier 66: Spiral Galaxy in the Leo Triplet

Messier 66 is the brighter, east side of the galaxy pair below Leo's hindquarters. It shares a low-power field with M65, and with the fainter NGC 3628 the three form the Leo Triplet.

What it is

M66 is a spiral galaxy about 35 million light-years away. Its visible disk covers about 8 by 2.5 arcminutes, which at that distance means it is roughly 80,000 light-years long. Unlike its calm neighbor M65, M66 has clearly been bent by the gravity of the other two galaxies. Its spiral arms look lopsided and appear lifted out of the galaxy's plane, and one arm seems to cross in front of the central bulge. Dust lanes and pink clouds of glowing hydrogen mark places where new stars are forming.

M66 is also a productive supernova host. SEDS lists five, found in 1973, 1989, 1997, 2009 and 2016; the brightest, in 1989, reached about magnitude 12.

When to see it

Look for M66 on spring evenings, March through May. It is highest around 9 p.m. in late April, when it stands about 63° above the southern horizon from 40°N. Lying just north of the celestial equator, it is visible from nearly everywhere on Earth, including the Southern Hemisphere, where it is an autumn object low in the north.

How to find it

Start at Chertan (Theta Leonis), the star at the bottom of the triangle that forms Leo's rear, about 5° south of Zosma. Iota Leonis, at magnitude 4, lies about 5½° south-southeast of Chertan. The galaxy pair sits at the midpoint between the two stars. M66 is the eastern one, about 20 arcminutes east and a little south of M65.

What you will see

Binoculars under dark skies can just show M66 as a faint spot; it is the easier of the pair. In a 70–100 mm telescope it appears as an oval glow, a bit broader and brighter than M65, with a brighter center. A 200 mm telescope begins to show its uneven shape: one end looks brighter, and with patience you may pick out a darker lane and some mottling along the edges. With NGC 3628 to the north, all three galaxies fit in a field about a degree wide. Light pollution dims it quickly, and no filter helps.

History

Messier cataloged M66 together with M65 on March 1, 1780. He wrote that he had passed right by both in November 1773 while tracking a comet that moved between them, probably missing them because of the comet's glare. Some sources credit Pierre Méchain with the find, but SEDS explains this as a later error. Halton Arp included M66 in his Atlas of Peculiar Galaxies as number 16, and the whole triplet as number 317.