In 1609, Galileo first telescopically observed the Beehive and was able to resolve it into 40 stars.
Charles Messier added it to his famous catalog in 1769 after precisely measuring its position in the sky.
Along with the Orion Nebula and the Pleiades cluster, Messier’s inclusion of the Beehive has been noted as curious, as most of Messier’s objects were much fainter and more easily confused with comets.
Another possibility is that Messier simply wanted to have a larger catalog than his scientific rival Lacaille, whose 1755 catalog contained 42 objects, and so he added some well-known bright objects to boost his list.[12]
Ancient Greeks and Romans saw this object as a manger from which two donkeys, the adjacent stars Asellus Borealis and Asellus Australis, are eating; these are the donkeys that Dionysos and Silenus rode into battle against the Titans.[13]
Hipparchus (c.130 BC) refers to the cluster as Nephelion (”Little Cloud”) in his star catalog.[14]
Claudius Ptolemy’s Almagest includes the Beehive Cluster as one of seven “nebulae” (four of which are real[15]), describing it as “The Nebulous Mass in the Breast (of Cancer)”.[16]
Aratus (c.260-270 BC) calls the cluster Achlus or “Little Mist” in his poem Phainomaina.[14]
This perceived nebulous object is in the Ghost (Gui Xiu), the 23rd lunar mansion of ancient Chinese astrology. Ancient Chinese skywatchers saw this as a ghost or demon riding in a carriage and likened its appearance to a “cloud of pollen blown from willow catkins”.
It was also known by the somewhat less romantic name of Jishi qi, the “Exhalation of Piled-up Corpses”.[14] It is also known simply as Jishi, “cumulative corpses”.
Morphology and composition
Like many star clusters of all kinds, Praesepe has experienced mass segregation.[6][10][17] This means that bright massive stars are concentrated in the cluster’s core, while dimmer and less massive stars populate its halo (sometimes called the corona).
The cluster’s core radius is estimated at 3.5 parsecs (11.4 light years); its half-mass radius is about 3.9 parsecs (12.7 light years); and its tidal radius is about 12 parsecs (39 light years).[6][10]
However, the tidal radius also includes many stars that are merely “passing through” and not bona fide cluster members.
Altogether, the cluster contains at least 1000 gravitationally bound stars, for a total mass of about 500-600 Solar masses.[6][10]
A recent survey counts 1010 high-probability members, of which 68% are M dwarfs, 30% are Sun-like stars of spectral classes F, G, and K, and about 2% are bright stars of spectral class A.[6]
Also present are five giant stars, four of which have spectral class K0 III and the fifth G0 III.[3][6][18]
So far, eleven white dwarfs have been identified, representing the final evolutionary phase of the cluster’s most massive stars, which originally belonged to spectral type B.[4]
Brown dwarfs, however, are extremely rare in this cluster,[19] probably because they have been lost by tidal stripping from the halo.[6]
The cluster has a visual brightness of magnitude 3.7. Its brightest stars are blue-white and of magnitude 6 to 6.5. 42 Cancri is a confirmed member.
Photo of comet C/2001 Q4 (NEAT) next to Messier 44
Planets
In September, 2012 two planets which orbit separate stars were discovered in the Beehive Cluster.
The finding was significant for being the first planets detected orbiting stars like Earth’s Sun that were situated in stellar clusters.
Planets had previously been detected in such clusters, but not orbiting stars like the Sun.
The planets have been designated Pr0201b and Pr0211b. The ‘b’ at the end of their names indicates that the bodies are planets.
The discoveries are what have been termed Hot Jupiters, massive gas giants that, unlike the planet Jupiter, orbit very close to their parent stars.
The announcement describing the planetary finds, written by Sam Quinn as the lead author, was published in the Astrophysical Journal Letters.
Quinn’s team worked with David Latham of the Harvard-Smithsonian Center for Astrophysics, utilizing the Smithsonian Astrophysical Observatory’s Fred Lawrence Whipple Observatory.[20]
In 2016 additional observations concluded that in the Pr0211 system there are actually two planets, the second one being Pr0211-c.[21]
So, he was messy-er than usual...............