The constellation Cancer is the faintest of the twelve constellations of the zodiac, and many casual stargazers pass it by when looking from bright Gemini to the striking group Leo to the east. In city skies, the constellation is hard to see at all. But there are some excellent sights in Cancer within reach of a telescope, including the superb star cluster M44, the Beehive Cluster, which is one of the finest objects for a wide-field telescope or a pair of binoculars.
To locate Cancer and the Beehive, first find the star Procyon in Canis Minor. To find this star, extend a line eastward from Bellatrix in Orion’s right shoulder through Betelgeuse in his left shoulder until you find a bright star. That’s Procyon. Now find the bright star Pollux in Gemini and imagine an equilateral triangle pointing eastward with Pollux at one apex and Procyon at another. The third apex, pointing east, lies in the constellation Cancer (see image below). In the northern hemisphere, Cancer is nearly overhead in the mid-evening hours; in the southern hemisphere, it’s low over the northern horizon.
The showpiece of the constellation Cancer is M44, the “Praesepe” (“PRAY-see-pay”) star cluster. It’s also called the “Beehive” cluster because it looks like a hive of bees. It is easily visible to the unaided eye in dark sky as a misty cloud just west of the mid-point between the stars Asellus Borealis and Asellus Australis.
One of the few star clusters known since antiquity, the Beehive was called the “Little Cloud” or “Cloudy Star” by the ancient Greek astronomer Hipparchus. The ancients used the cluster as a weather indicator: if it was invisible, then violent storms were said to be on the way.
Unlike the Pleiades, M45, this cluster can’t be resolved into individual stars with the unaided eye. Its true nature and striking beauty are revealed only with help of binoculars or rich-field telescope. Galileo was first to turn a telescope toward this “nebulous” object, and reported: “The nebula called Praesepe, which is not one star only, but a mass of more than 40 small stars.”
The cluster lies about 580 light years from Earth and stretches 16 light years across. It appears about 1.5o across (about 3x the size of the full moon), so examine it with your binoculars or telescope with a low-power eyepiece to see its full glory. It is a very fine object for binoculars.
With larger telescopes, more than 200 stars have been confirmed as members. Astronomers determine which stars are members of the cluster by measuring the common motion of the stars… if they’re all going in the same direction, they’re assumed to be from the same cluster.
The Beehive emerged out of a great diffuse gaseous nebula some 730 million years ago. Some believe it has a common origin with the Hyades cluster, which forms the “V” in Taurus, a constellation well to the west. The two clusters have since separated, but they’re still headed in the same direction.
Because of its nebulous appearance to the unaided eye, the ancient Japanese believed the cluster was a lump of souls, and the sight of it terrified them. It’s called seki shiki in Japanese which translates as “piled corpse spirits”.
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