Meet M3 The Magnificent, A Spring Showpiece


Located 33,900 light years from Earth in the constellation of Canes Venatici the Hunting Dogs, M3 is one of the best and brightest globular clusters in the sky for beginning observers. It’s well-placed for viewing in April starting about 9:30 p.m. local time. Adam Block, Mount Lemmon SkyCenter, U. of Arizona

Lots of star clusters, nebulae and galaxies have nicknames based on their beauty, appearance and location. For instance, we have the Eagle Nebula, Fish on a Platter, Hamburger Galaxy and Ant Nebula. What an oversight then that M3, one of early spring’s most magnificent globular clusters, has no name. We only know it by its number in a catalog of comet lookalikes compiled by 18th century French astronomer Charles Messier’s. It was the third object in a tally of 110. Here’s his original description:

“On May 3, 1764, when working on a catalog of the nebulae, I have discovered one between Bootes & one of the Hunting Dogs of Hevelius, the southernmore of the two, exactly between the tail & the paws of this Dog, according to the charts of Flamsteed. That nebula which I have examined with a Gregorian telescope of 30 pouces (inches) focal length, which magnifies 104 times, doesn’t contain any star; the center is brilliant, & the light gets lost fading [outward]; it is round, & could have 3 minutes of arc in diameter.”

M3 is easy to find. Look high in the northeastern sky for the Big Dipper. Follow the curve of the handle downward to Arcturus, a bright, orange-colored star. You can’t miss it. Then take a pair of binoculars, focus it first on Arcturus, then sweep upward toward the star Cor Caroli (magnitude 2.8), the brightest star in the Hunting Dogs. Not quite midway between them, you’ll run into a fuzzy spot — that’s M3! Stellarium

Messier described what he saw in all-we-want-are-the-facts-ma’am prose like Sgt. Joe Friday in TV’s Dragnet. We can’t really blame him. He was only using a 4-inch refracting telescope with probably no where near the optical quality of today’s instruments. At least his skies were dark!

M3 is one of the brightest, richest globular clusters in the northern sky. I routinely stop by for a look in my telescope a dozen times a season. Globular clusters are the cosmic equivalent of busy beehives. Containing anywhere from tens of thousands to 10 million stars, they’re densely packed spheres of stars held together by gravity. Most of them dot the outer halo of the Milky Way galaxy many thousands of light years from Earth. Although we know of about 152 globulars in our galaxy, thousands of others have been sighted in the halos of other galaxies.

This is the view through binoculars as you face east. Stellarium

You can see M3 (magnitude 6.2) in binoculars even from suburban skies. It looks like a fuzzy, unfocused star right next to a real star (see binocular view below). I know this is hard to believe, but this clotted, creamy glow is composed of half a million stars in a ball 180 light years across or nearly 5 times the distance from here to the star Arcturus. Through a 4-inch telescope, you can see the cluster has a brighter core and fainter “halo.” If you look closely at the halo with averted vision (glancing off to the side rather than staring directly at it), it will appear rich with faint stars that come and go as you move your eye about.

Larger telescopes in the 6 to 10-inch range show hundreds of faint stars resembling diamond dust that sparkle and shimmer around the bright center like frost crystals on a windowpane. Like most globulars, the larger the instrument the more stars revealed or “resolved” in the parlance. Seeking views of deep space objects like M3 that more closely approach appearances in photographs is one of the drivers that makes amateurs dream of owning a larger telescope.

The core of the globular cluster M3 through the eye of the Hubble Space Telescope. NASA, ESA, STScI and A. Sarajedini (University of Florida)

My largest is a 15-inch (37-cm) reflector that can see just about anything. But after poking around with a friend’s 24-inch, I’d love to own one of those too! Maybe some day. Globular clusters really come alive in larger instruments. In the meantime, you and I will make the most of what we have. No matter the instrument, if you use it regularly and push yourself to see a little more, you’ll often succeed way beyond expectations. I like to use photos of clusters or nebulae to challenge myself to find these extra details.

I hope you enjoyed our brief sojourn to this faraway cluster. As the Orion Nebula and Pleiades amble west, it’s time to face east and greet the new faces in the neighborhood. If you have a suggestion for a name for M3, send it my way either by e-mail at or use the Comments area. I’ll rev up the PR machine and see what I can do.

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