M 44 - Beehive Cluster Praesepe
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M 44 - Beehive Cluster, Praesepe

February 18, 2005
Open Cluster M44 (NGC 2632), type 'd', in Cancer

Right Ascension: 08 : 40.1 (h:m)
Declination: +19 : 59 (deg:m)
Distance: 0.577 (kly)
Visual Brightness: 3.7 (mag)
Apparent Dimension: 95.0 (arc min)

Known to Aratos 260 B.C.

This famous cluster, M44, is also called Praesepe (Latin for "manger"), or the Beehive cluster. It is also one of the objects easily visible to the naked eye, and thus known since prehistoric times. Some ancient lore is associated with it: Greeks and Romans saw this "nebula" as the manger (Greek: Phatne) associated with two asses who eat from it, Asellus Borealis, the Northern Ass (Gamma Cnc; Spectral type A1 V, mag 4.7, distance 155 ly) and Asellus Australis, the Southern Ass (Delta Cnc; Spectrum K0 III, mag 3.9, distance 155 ly). Erathosthenes reported that these were the asses on which the gods Dionysos and Silenus rode into the battle against the Titans, who were frightened by the animals' braying so that the gods won. As a reward, the asses were put in sky together with Phatne. Aratos (260 B.C.) mentioned this object as "Little Mist", Hipparchus (130 B.C.) included this object in his star catalog and called it "Little Cloud" or "Cloudy Star." Ptolemy mentions it as one of seven "nebulae" he noted in his Almagest, and describes it as "The Nebulous Mass in the Breast (of Cancer)". According to Burnham, it appeared on Johann Bayer's chart (about 1600 A.D.) as "Nubilum" ("Cloudy" Object).

Galileo has first resolved this "nebulous" object, and reported: "The nebula called Praesepe, which is not one star only, but a mass of more than 40 small stars." It was probably later seen and partly resolved in 1611 by Peiresc, the discoverer of the Orion Nebula (M42), and observed as a cluster by Simon Marius in 1612. Charles Messier added it to his catalog on March 4, 1769.

With larger telescopes, more than 200 of the 350 stars in the cluster area have been confirmed as members (by their common motion). Some others are foreground or background stars, and others may not yet have been determined.

According to the new determination by ESA's astrometric satellite Hipparcos, the cluster is 577 light years distant (previous estimates have been at 522 light years), and its age was estimated at about 730 million years. Curiously, both this age and the direction of proper motion of M44 coincide with that of the Hyades, another famous naked-eye and longly known cluster, which however was neither included in Messier's list nor in the NGC and IC catalogs, which is currently estimated at an age of about 790 million years (older estimates had given, for both clusters in each case, an age of 400 and 660 million years). Probably these two clusters, although now separated by hundreds of light years, have a common origin in some great diffuse gaseous nebula which existed 700 to 800 million years ago. Consequently, also the stellar populations are similar, both containing red giants (M44 at least 5 of them) and some white dwarfs.

M44 also contains one peculiar blue star. Among its members, there is the eclipsing binary TX Cancri, the metal line star Epsilon Cancri, and several Delta Scuti variables of magnitudes 7-8, in an early post-main-sequence state. Look at our list of the brightest stars of M44.

The Praesaepe cluster was classified by Trumpler as of class I,2,r (according to Kenneth Glyn Jones), as II,2,m by the Sky Catalog 2000, and as class II,2,r by Götz.

As mentioned in the description for the Orion Nebula M42, it is a bit unusual that Messier added the Praesepe cluster (together with the Orion Nebula M42/M43 and the Pleiades M45) to his catalog, and will perhaps stay subject to speculation.

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