The dim constellation of Cancer, the Crab, high toward the south during the mid-to-late evening hours now, is the least conspicuous of the 12 zodiacal constellations. Aside from being in the Zodiac, it is probably only noteworthy because it contains one of the brightest star clusters in the sky. The cluster appears to the eye as a fuzzy patch of light, but binoculars will reveal its stellar nature.
Officially called M44, the cluster has a curious naming history. Some astronomy texts speak of "Praesepe, the Manger," while others simply call it the "Beehive." A manger is defined as "a trough in which feed for donkeys is placed." The cluster was apparently first called Praesepe 20 centuries ago.
Indeed, two nearby stars, Gamma and Delta Cancri are also known as Asellus Borealis and Asellus Australiis the northern and southern ass colts feeding from a manger.
Swarm of celestial bees
able --> Galileo first resolved Praesepe into stars (36 of them) in 1610. More than 100 stars can be seen in binoculars or a small telescope and they seem to be spread out over an area about three times the apparent diameter of the Moon.
The cluster developed an unusual moniker, apparently almost four centuries ago, when some anonymous person, upon seeing so many stars revealed in one of the first crude telescopes, exclaimed, "It looks just like a swarm of bees!"
Some astronomy books now call the cluster "Beehive," while others still call it "Praesepe."
The cluster of stars, hundreds in all, is about 580 light-years away, and spans about 10 light-years across in space.
Harbinger for storms
Interestingly, Praesepe was also used in medieval times as a weather forecaster. It was one of the very few clusters that were mentioned in antiquity.
Aratus (around 260 B.C.) and Hipparchus (about 130 B.C.) called it the "Little Mist" or "Little Cloud." But Aratus also noted that on those occasions when the sky was seemingly clear, but Praesepe was invisible, that this meant that a storm was approaching.
Of course, we know today that prior to the arrival of any unsettled weather, high, thin cirrus clouds (composed of ice crystals) begin to appear in the sky. Such clouds are thin enough to only slightly dim the Sun, Moon and brighter stars, but apparently just opaque enough to hide a dim patch of light like Praesepe.
Roughly 3,000 years ago, the point in the sky marking the position of the June solstice lay very close to Praesepe. But thanks to precession -- the "wobble" that the Earths axis describes over an interval of 25,700 years -- the solstice point has shifted out of Cancer and is now located in the adjacent constellation of Gemini, having apparently slid backward toward the west over the last three millennia.
The crab is a creature that can go in one direction just as well as another, so it seems only fitting that this part of the sky, where the Sun has seemingly reversed its direction at the beginning of summer, has since been dedicated to this animal.
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