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M41, An Open Cluster in Canis Major

TargetTypeR. A.Dec.ConstellationMagnitudeSize
M41 (NGC 2287)Open Cluster06h 46m 01s-20° 45′ 00″Canis Major4.539 arcmins

Overview

M41, the open cluster also known as the Little Beehive Cluster is bright enough that it may first have been recorded by Aristotle in 325 BC. We know it was ‘discovered’ by Giovanni Batista before 1654. Messier himself observed it in January 1765 and recognized it as “no more than a cluster of faint stars”.

That description downplays the beauty of this large, bright cluster hovering near the brightest star in our sky, Sirius (Alpha Canis Majoris). Sirius is easy to find because it shines at magnitude -1.4, making it brighter than everything else, except the moon, Venus, Jupiter and, occasionally, Mercury and Mars.

The cluster itself, the only Messier object inside this small constellation, shines at magnitude 4.5, placing it comfortably within naked-eye visibility, even under moderately light-polluted skies. This makes it a great target for us as we begin to venture back outside for evening stargazing as winter gives way to spring. The brightest individual star shines at magnitude 6.9, just beyond what we can see unaided, which is why this cluster appears to us as a small, smokey patch of sky.

Covering an area of sky larger than the full moon, there are about 100 stars squeezed into a region of space with a diameter of about 25 light-years. The stars in this cluster include many red giants – which you can tell from their colors in the image below – and that gives a clue to its age, which is approaching 200 million years.

While this cluster is expected to hold together for another 300 million years, it is today 2,300 light-years away and receding from us all the time at the rate of 15 miles (23 km) per second.

M41, an open cluster in the constellation Canis Major.

Finder Charts

This first sky chart, from SkySafari 6, shows the sky looking south at 9:00 p.m. in mid-February.

To locate M41 we need to first find Sirius. This is the brightest star in the night sky, so it’s fairly easy to track down in the south right now. But, if you’re not immediately sure you’ve got the right star, use the unmistakable shape of Orion (ringed orange) to help, his three ‘belt’ stars roughly point the way to Sirius.

Stars on this chart are shown to magnitude 5.0 and the moon and planets are not shown.

[M41-1] Tracking this cluster down begins with finding Sirius. Click for full-screen.

M41 is practically due south of Sirius and easy to see in binoculars or a magnifying finderscope. If yoiur sky is dark enough and you’re eyes are dark-adjusted, you can even see it with no optical aid.

From Sirius, find the bright star Murzim (Beta Canis Majoris) which shines at magnitude 2. M41 is the third point of a roughly equilateral triangle with Sirius and Murzim forming the other two corners.

For further help in finding it, look for the fainter (but still visible to the naked eye) Nu2 Canis Majoris. It is halfway along an imaginary line connecting Murzim to M41.

You can also look for Omicron2 Canis Majoris, a magnitude 3 star. Connect it with an imaginary line to Sirius and M41 is jst to the right of the midpoint of that line.

[M41-2] Using the bright stars Sirius, Murzim and Nu2 CMa., it’s straightforward to get M41 in the eyepiece. Click for full-screen.

Stars are shown to magnitude 7 in this final star chart. We can see an additional marker for locating M41 on the line connecting Sirius to Omicron2 CMa. Two stars, both just a little brighter than magnitude five are about midway between the two brighter stars. M41 is in line with these two stars, Pi Canis Majoris and 15 Canis Majoris.

[M41-3] Two fainter but still naked eye stars help us hone in on the right spot. Click for full-screen or download the pdf below.

Now you have this beautiful cluster in your eyepiece, what should you expect to see?

Individual Telescope Views

The following views will help you find M41 in different telescope types by presenting the images as your telescope will show them. The first image is with a black sky and white stars, the second picture is the same image but presented in inverse monochrome. Black stars on a white background is often easier to use at the telescope. Stars are shown to magnitude 12.0, revealing individual stars in the cluster itself. The stars Pi CMa and 15 CMa are shown in each image.

Each image can be clicked on for a full-screen version.

Upright View – This is what your eyes see unaided and through a reflex or red-dot finderscope

[M41-4]
[M41-5]

Upside-down view – This is what reflectors and magnifying finders show, and refractors / Cassegrains without a star diagonal

[M41-6]
[M41-7]

Mirrored View – Refractors and Cassegrain models with a star diagonal show this view

[M41-8]
[M41-9]

Observation

Some of the stars in the cluster can be resolved in a pair of binoculars and a small telescope will do a good job of conveying the beauty of this object to your viewing eye.

Ten of the stars are brighter than magnitude eight, and the next fifty are brighter than magnitude 13, putting them well within resolving reach of most telescopes. One immediate challenge on centering this cluster is to pick out the different colored stars, particularly hunting the more obvious ambers and russets of the red giants.

Next, look for patterns amongst the generous sprinkling of delicate stars. Can you see what looks like a reversed question mark, and what about a parallelogram shape; do you see that in the star cloud?

Finally, how many of these pinprick jewels can you see. If you take your time, you could push the number beyond 70!


PDFs for Printing

Each of the star maps above is reproduced as a pdf below. Each star map has a number in [square brackets] beneath it which corresponds to the file number below. If you want image [M41-1], for example, click the ‘download’ button next to it below and you’ll be able to open it as a printable pdf.

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