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Binocular Universe: Going to the Dogs

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Binocular Universe: Going to the Dogs

February 2015

Phil Harrington

As the owner of three dogs, I always look forward to the annual Westminster Dog Show held every February in New York City. Westminster attracts thousands of the finest canines from around the globe to vie for the coveted title of Best in Show.

Above: Winter star map from Star Watch by Phil Harrington.


Above: Finder chart for this month's Binocular Universe.

Chart adapted from Touring the Universe through Binoculars Atlas (TUBA)
Click the chart to display at full size. Chart will display in a separate tab.


The sky also puts on its own dog show every winter. We have Canes Venatici, the Hunting Dogs, rising in the northeast, Canis Minor, the Small Dog, high in the south, and Canis Major, the Large Dog, in the south-southwest. Canis Major, home to the brightest star of night, Sirius, easily wins our celestial best in show. Prepare to be astounded when you first spot Sirius through your binoculars. No, you won't see its famous white dwarf companion, but it's still quite a dazzler! Sirius, a white, type A star, lies only 8.5 light years away.

Shift Sirius toward the top (north) of the field and then take a look near the bottom (south) for a clump of faint stars. That's the open cluster M41. For astro-history buffs, M41 was actually discovered by the Greek scientist Aristotle (384 BC - 322 BC) in 325 B.C. Today's 50-mm binoculars reveal about 20 faint stars sparkling like tiny fragments of diamond dust within its distant boundaries. If you are using 70-mm or larger binoculars, you may notice that one of the group's brightest stars near the center glows with a subtle reddish tint, while others show hints of yellow and orange.

Continue southward along the dog's back until you come to Omicron-1 and Omicron-2 Canis Majoris. Yellowish Omicron-1 is the brightest member of the sparse open cluster Collinder 121. Owing to the star-filled surroundings, this group is much tougher to isolate than M41. Look carefully for a pair of 6th-magnitude suns just to the south of Omicron-1, and three 7th-magnitude and fainter stars in a triangle to the northwest.

Hop another half a field southeast to 2nd-magnitude Wezen (Delta Canis Majoris), the dog's tailbone, and then up and over half a field northeastward to 4th-magnitude Tau Canis Majoris. Tau is the brightest star in the open cluster NGC 2362. Unfortunately, the light from this beacon overwhelms the other 40 or so tightly packed cluster stars through 10x and lower binoculars, but a few faint points peak through my 16x70s. NGC 2362 is only 5 million years old, making it one of the youngest star clusters known. Tau, a blue supergiant, is the brightest member by far. In fact, Tau is one of the most luminous stars in the heavens, shining 50,000 times brighter than our Sun.

Wezen forms a naked-eye triangle with the stars Adhara (Epsilon Canis Majoris) and Aludra (Eta Canis Majoris). Adhara is often portrayed as one of the dog’s hind leg, while Aludra is the tip of its tail.

Although the area is littered with stars, a singularly spectacular reddish star floats just northeast of Adhara, the triangle's westernmost point. The late Tomm Lorenzin, author of the 2000+ on-line observing guide (www.1000plus.com/2000plus), described it as "a bright, ripe kumquat." Tomm's kumquat, known officially as Sigma Canis Majoris, contrasts beautifully with the surrounding white and blue-white stars.  Sigma is a spectral class M1.5 Iab late stag red supergiant star. Having fused all of its hydrogen into helium and heavier elements, the star's hydrostatic equilibrium has been compromised. As a result, it has expanded to more than 400 times our Sun's diameter, moving up and to the right on the Hertzsprung-Russell diagram.

Search half a binocular field south of Aludra for a right triangle of three bright stars accompanied by many fainter points. This little-known star cluster is an easy target through just about any pair of binoculars. Its large size and sparseness, however, masked its true nature until 1931, when Swedish astronomer Per Collinder included it as number 140 in his catalog of widespread star clusters. The 30 stars in Collinder 140 range in brightness from 5th magnitude to fainter than 9th and form a triangle measuring about 3/4° across. Arizona deep-sky observer Steve Coe suggests the nickname "The Tuft" because of its location at the very tip of the dog's tail.

You may notice another gathering of stars about 2 degrees northwest of Cr 140. That's Collinder 132. Through my 10x50s, I count 14 stars scattered across about 1.5 degrees. Four of the stars form an obvious triangle plotted on the chart above, while the rest lie about. Whether or not this is a true cluster or just a fortuitous alignment of randomly distanced stars remains an unsolved mystery. But no matter, they make a nice chart for 7x-10x binoculars.

Finally, drop southward another binocular field to the southwest, just across the border into Puppis, to find the open cluster Collinder 135. Its brightest member, 3rd-magnitude Pi Puppis, is classified as an orange supergiant (spectral class K3 Ib to be exact) and also stands out nicely among the other blue-white cluster stars. Cr 135 also includes the double star v1 and v2 Puppis, just north of Pi, and a solitary 5th-magnitude star to the west that collectively give the cluster a distinctive arrowhead shape.  Given a good view to the south, Cr 135 will no doubt become one of your winter favorites, a hidden secret for binocular observers that is completely missed by those stuck viewing through telescopes alone.

There are so many other binocular targets in this portion of the winter sky that's hard to know where to begin.  We haven't even scratched the surface!  Take a look at the long list below of what awaits you!

Until next month, remember that two eyes are better than one!

About the Author:

Phil Harrington has written 9 books on astronomy, including Star Ware, Star Watch, and his latest, Cosmic Challenge.  Visit his web site, www.philharrington.net, for more information.


  • okiestarman56 and Ahab like this


Hi Phil;


I agree that there is lots of see among the dogs, mostly the big one.   As usual, an excellent article with lots of fun stuff to view.


I have called Col 140 "The Tuft in the Tail of the Big Dog" for years.  From dark skies this naked eye cluster is a rather large glow just under the tail star of Canis Major.


Take Care;

Steve Coe

    • Ira likes this

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