The Beehive Cluster: A swarm of 1,000 stars
Although it’s one of the 12 zodiac constellations, Cancer the Crab is so faint that you’d likely never notice it … except for the lovely star cluster in its midst. This cluster is commonly known as the Beehive, or M44. Astronomers know it as NGC 2632. An older name is Praesepe (manger or crib in Latin). The Beehive is a wonderful swarm of stars, glimpsed with the eye alone in a dark location. You can see it easily in binoculars. Its size is 1.5 degrees, or three full moon diameters. Although the eye cannot detect them all, it contains a thousand stars.
How to see the Beehive star cluster
Keep an eye out for Regulus, and the Gemini stars Castor and Pollux, for they’re your guide stars to the Beehive star cluster. The Beehive star cluster is halfway between Regulus and the Castor-and-Pollux pair.
In March, look in the east after dark. You’ll probably see Regulus, the brightest star in the constellation Leo, rather close to the eastern horizon. Then the bright stars Castor and Pollux in the constellation Gemini will catch your eye higher up in the eastern sky.
As the months pass, the Beehive will climb higher in the evening sky. It disappears from the western evening sky in late June, and returns to the eastern morning sky starting around late August.
You’d think that an object with so many names – NGC 2632, M44, Praesepe, Beehive – would be bright. But only in dark country skies can you see this faint fuzzy object with the unaided eye. However, binoculars magically transform this smudge of light into a glittery swarm of stars.
The Beehive’s 1,000 stars
There are approximately 1,000 stars in the beautiful Beehive cluster, which is an open cluster of stars in our galaxy. Open clusters are stars that are gravitationally bound and are created out of the same star-forming nebula, such as the stars in the Orion Nebula. The Beehive is one of the nearest open clusters to our sun and Earth. It has a larger population of stars than most other nearby clusters.
Planets in the Beehive Cluster
Becky Smethurst of University of Oxford discusses Messier 44 and the discovery of planets around stars in the open cluster.
In 2012, the Kepler Space Observatory found two planets in the Beehive. The planets orbit two different stars. The planets’ designations are Pr0201b and Pr0211b. Both of these planets are hot Jupiters, that is, massive gas giants, in both cases orbiting very close to their stars. These two were the first planets astronomers detected orbiting stars like our own sun that were situated in an open star cluster. Since their discovery, Kepler has found four more exoplanets orbiting stars in the Beehive.
History and mythology of the Beehive Cluster
As early as the second century C.E., Ptolemy wrote that the Beehive star cluster was:
… the nebulous mass in the breast of Cancer.
In ancient times, people used the cluster as a weather predictor. Pliny said:
If Praesaepe is not visible in a clear sky, it is a presage of a violent storm.
Galileo had the first telescopic view of the Beehive in 1609. With his paper tube and two pieces of glass, he was able to detect 40 stars.
Around 1769, Charles Messier added the cluster to his famous catalog of nebulous objects. Hence the designation M44: the 44th object in Messier’s catalog.
The Beehive star cluster was a manger in Greek and Roman mythology. You might notice two bright stars on either side of the cluster with your binoculars, or you might see them with the unaided eye in dark skies. These two stars are Asellus Borealis and Asellus Australis. In skylore, they represent the donkeys that Dionysus and Silenus rode into battle against the Titans.
Bottom line: The Beehive Cluster is an open cluster that lies near the center of the constellation Cancer the Crab. It goes by many names, including Praesepe and M44.