M50 Star Hop: Finding the Open Cluster from Sirius with a 114-150 mm Reflector

Before you start

M50 is best placed in February and March, when it is high enough in the evening sky to observe comfortably. Outside those months it sits lower in the evening, and in some months it is close to the glow of twilight, so plan around the season you are observing in.

Its altitude depends on your latitude. At its highest, the cluster reaches about 47 degrees above the horizon from 35 degrees north, about 32 degrees from 50 degrees north, and about 63 degrees from 35 degrees south. From 50 degrees north, the cluster is low, so you need a clear view toward the south. Trees, buildings and street lights along that horizon will cut into your observing time. From 35 degrees south, the cluster is well placed, and the same steps apply.

Choose a time when Sirius is well above the horizon in your part of the sky. The whole route depends on that first star, and it is much easier to start from a bright, high reference than from one that is low and hazy.

Let your eyes adapt to the dark for about ten to fifteen minutes before you start. Use a red light if you need to read a chart or adjust the telescope, since white light will undo that adaptation.

The star-hop route

The route has two hops. Both are short, and both start from stars you can identify without a chart once you know the pattern.

Step 1: Find Sirius

Sirius is the brightest star in the night sky and is very easy to find. It is in Canis Major, below and to the left of Orion's belt when you face south in the evening. Use the bright stars of Orion as a guide: follow the line of the belt down and to the left, and Sirius is the very bright white star you reach next.

Center Sirius in your finder. Then check the low-power eyepiece on the telescope. At 25 to 40 times, Sirius should be a single, sharp point. If it looks smeared, focus carefully before you go on.

Step 2: Reach Muliphein

Muliphein, Gamma Canis Majoris, is a fourth-magnitude star about 5 degrees east of Sirius. That is roughly half a fist held at arm's length. Sirius and Muliphein are not hard to tell apart, because Sirius is far brighter, and Muliphein is the nearest moderately bright star in that direction.

Move your telescope or finder slowly from Sirius toward the east until Muliphein is centered. Check the view at low power: Muliphein should sit alone in a field with a few faint companions, not in a crowd. If you find a dense group of bright stars, you have overshot, so return to Muliphein by going back west.

Step 3: Move north to M50

From Muliphein, M50 lies about 7 degrees almost directly north. The offset is small, so keep your movement in a straight line up from the star. It is slightly east of due north, and you will not need to correct much.

Use a wide-field finder for this hop if you have one. The cluster should appear within a finder field of about 5 to 6 degrees, so you can see the target before you switch to the telescope's eyepiece. Once M50 is in the finder, center it precisely, then move to the eyepiece.

A cross-check from Sirius

You can also reach M50 directly from Sirius. The cluster is about 9 degrees from Sirius, toward the north-northeast. This route is a useful check. If the two hops land you at the same spot, the cluster should be where the direct line from Sirius points as well.

If you can see Muliphein in your finder while you are moving north, you are on the correct path. If you cannot, return to Sirius and try the first two steps again.

What you will see

At low power, M50 is not a hazy glow. It appears as a scatter of individual stars, which is why this equipment class is well suited to it. Expect a group of stars spread over an area of about a quarter of a degree, with no single bright member dominating the view.

The brighter members are faint compared with Sirius and Muliphein, and in a suburban sky, the cluster's brightest stars will be only just visible against the background. The fainter members are harder to pick out, and they may appear as a general texture or grain rather than as separate points. Do not expect the cluster to look dense or richly populated. Its appeal is in the pattern of stars, not in brightness.

Star colors are also worth a look. Some members show a slight difference in tint, but this is subtle, and you will need a steady view and a moderate magnification to notice it.

Confirming you have arrived

Several checks will tell you whether you are on the cluster or simply near it.

First, compare what you see with what is expected. If you are on M50, you should see a loose group of stars that are clearly more numerous than the background stars around them. If the field shows only scattered, evenly spread stars with no clear clustering, you are probably a few degrees off.

Second, try moving the telescope in small steps around the expected position. A true cluster will hold together as you move, with its member stars staying in the field and the group's outline changing gradually. A random star pattern will change quickly, and the stars will not form a consistent group.

Third, switch to a slightly higher magnification. At 60 to 80 times, the cluster should still be recognizable as a group, and the individual stars should be sharper. If the cluster falls apart or disappears, you may have stepped away from the center, so return to the spot where the group was clearest.

If you are still unsure, return to Muliphein and repeat the hop north. Once you know the exact field pattern, you can find it again more quickly next time.

Equipment and eyepiece choice

A 114 to 150 mm reflector is more than adequate for resolving M50's members. In this case, the star hop matters more than aperture, because the cluster is simply a matter of getting to the right place.

Start with a low-power eyepiece, around 25 mm. On a typical reflector of this class at f/8 to f/10, that gives roughly 40 to 50 times, with a field of view of about 1.3 degrees. At that power, M50 fills only a small part of the field, which is what you want for a first look. A higher-power eyepiece can narrow the field too much to find the cluster easily.

A finder with a wide field of view, such as a small finder-scope or a finder-style red-dot device, helps you move from Muliphein to the cluster. If your telescope has a finder-scope with a narrow field, consider a low-power eyepiece for the final steps instead.

Keep the telescope on a stable mount, and make small, slow movements. Watch for vibrations when you touch the tube, and let the view settle before you judge what you see.