Astronomy: A stargazer’s guide to Canis Major


Spring is about to dawn, thank goodness, or so at least the calendar says. However, in the early evening, the stars of winter still linger a while longer. Now is the time to go out and see them if you don’t want to wait until November.

The best thing about the late winter, astronomically speaking, is the winter Milky Way. This silvery streak represents billions of stars in our galaxy that are too far away to resolve with the unaided eye.

One of the best places to scan is in the direction of Canis Major, the Big Dog. Look toward the south fairly low on the horizon for the night sky’s brightest star, Sirius, the Dog Star. You’ve found the head of Canis Major.

This region of sky is particularly rich in open clusters, densely packed collections of stars. Each cluster was born of the same enormous cloud of hydrogen gas. Eventually, most of the stars will drift apart. The fact that they are still close suggests they are recently born.

The easiest cluster to find is M41. Look below Sirius with binoculars for a lumpy patch of light. A small telescope will reveal a loose collection of about three-dozen stars.

The stars in M41 are about 100 million years old. Stars such as our sun last about 10 billion years, so these stars are celestial babies.

The cluster is relatively distant at about 2,500 light-years away (a light-year is about 6 trillion miles.). It contains about 100 stars packed into a space about 20 light years wide.

Above and slightly to the left of Sirius is M50. From dark, rural skies, you may just be able to see it in binoculars as a hazy ball of light.

In a small telescope, you’ll see about a dozen of the 100 stars in M50. Look especially for a pretty, reddish star at the southern tip of the cluster. Most of the other stars should have a bluish tint, indicating that this cluster is a very young one at about 50 million years old.

We see fewer stars in M50 partly because it is farther away than M41. At 3,000 light years distant, the stars of M50 are also packed into a much smaller space 10 light years wide.

Viewing the cluster NGC2362 requires a telescope. Point it at the faint star Tau near Canis Major. Surrounding Tau is a beautiful sprinkling of faint stars. NGC 2362 is about 5,000 light years distant and at 5 million years old, it is among the youngest clusters.

To the left of NGC2362, the cluster M93 will just be visible as a faint fuzz ball in binoculars. In a small scope, you will see a band of about 20 fairly bright, densely packed stars.

This cluster of 250 or so stars is strewn across a 20-light-year section of sky. It lies about 3,500 light-years distant from Earth. At 100 million years old, it is among the oldest of the bright clusters in the direction of Canis Major.

I’ve saved the best for last. Two open clusters, M46 and M47 are to the left of Canis Major’s head and fit nicely into the field of wide-angle binoculars. M46 appears as a small cloudy patch. M47 is larger and brighter.

In a small scope, M47 resolves into a few conspicuous stars. M46 looks like dozens of speckles of light with hundreds of other stars just visible. The effect is spectacular as the unresolved stars weave a glow among the visible stars.

M47, at 1,500 light-years away, is three times closer than M46, but M46 has five times more stars. M47’s 50 stars seem more spread out because of their proximity to us.

There you go. You perhaps went outside dreading the chill. You’ll go back to the warmth of your home with stars in your eyes.

Tom Burns


Tom Burns is director of the Perkins Observatory in Delaware.

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