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Faint, fuzzy object near Sirius is a star cluster


Tonight for January 10, 2016

Tonight, look for the sky’s brightest star, Sirius, and the faint star cluster near it. Sirius is easy to see because it’s so bright and because the three prominent Belt stars in the constellation Orion – three stars in a short, straight row – always point to it. A reader wrote:

I went to study the constellation Orion, but first I had to see the star Sirius. There was a glimmer below Sirius, and upon looking, it seemed to be a very nice comet. Has anyone else seen this? I am a newby … and would like someone to verify if they see this. I am quite up and excited.

There is a comet in the sky now (Comet Lovejoy), but that fuzzy spot near Sirius isn’t a comet. It’s the lovely star cluster called Messier 41 or M41. This cluster lies about four degrees almost exactly south of Sirius. So the identification as a comet was wrong, but it is a reasonable mistake. The nuclei of comets look like fuzzy patches, much like M41 in a small telescope.

View larger. | The bright star is Sirius in the constellation Canis Major, the Greater Dog. The star cluster M41 can be seen as a fuzzy object below right of Sirius. Photo by EarthSky Facebook friend Stacy Oliver Bryant. Thank you Stacy!

The confusion with a comet and this cluster is not a new one. In the late 1700s, Charles Messier gave this object the number 41 on his list of “objects to avoid.” He was a comet hunter who wanted others to realize that this object, which looks like a comet, really isn’t.

Giovanni Batista Hodierna is said to have discovered M41 sometime before 1654, but it may have been known to individuals with particularly good vision throughout human history. The cluster – whose true diameter in space covers about 25 light-years – contains about 100 stars including several red giants.

Like most open star clusters of this type, it is relatively young – probably between 190 and 240 million years old. By contrast, our sun is thought to be four-and-a-half billion years old.

At mid-northern latitudes, Sirius and M41 stay out till roughly 3 to 4 a.m. local time.

So enjoy Orion, the star Sirius and M41 on these cold winter evenings. There are over 100 of the so-called Messier objects or M-objects known today. Today’s amateur astronomers consider them among the most prized objects to be viewed through binoculars and small telescopes. Here’s a list of M-objects. Advanced amateurs can observe them all and can earn a Messier certificate from the Astronomical League.

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Bottom line: No matter where you are on Earth, look for the sky’s brightest star, Sirius, in the month of January. If your sky is dark enough, notice the faint fuzzy object near the bright star Sirius. This object is called M41, and it’s a distant cluster of stars.

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