Object: M44 (Praesepe, Beehive cluster, NGC 2632)

Diameter in '
Number of stars
Brightest star (magnitude)
Distance in parsecs (3.26Ly)
: Cancer
: 08 40.0 / +19 40
: 70
: 3.1
: 161
: 6
: 158

Details sketch
Date / Time
Observing Location
Seeing / Transparency
Magnification / Field of View '
: 18/03/09 / 21:00
: Landgraaf
: 3 / 3
: Tal 100RS
: 35mm Panoptic
: 28 / 142
Stacks Image 1555
Stacks Image 1556

Move mouse pointer over image to see individual stars labeled

Observing report
M44, also known as Praesepe, is a large and bright open cluster that is very easy to locate. Tonight I can see it as a faint smudge of light just using my naked eyes. Praesepe (also know as the Manger) is clearly visible as a round, or using averted vision, a more oval glow between two 4th magnitude stars, delta and gamma Cancri. In the 4-inch refractor at the lowest possible magnification this large open cluster is very well detached from the background, a wonderful view. This low magnification of 28x is achieved with the 35mm Panoptic, and is also used for making the sketch. M44 is a huge cluster, more than 1 degree, and in the 4-inch refractor with a field of view of 2.2 degrees I count more than a hundred stars. This makes it a rich cluster. The range of brightness of the stars is huge. The brightest stars are of magnitude 6, the faintest of magnitude 12. I see no glow of unresolved background stars or nebulosity.

There are many double stars and other geometric forms, like triangles and semi-circles, visible. South of the centre of Praesepe I see 4 bright white stars in an asterism that reminds me of the Keystone asterism in Hercules. Only this keystone hangs upside down. A lot of stars are arranged in chains, and there are definitely empty spaces visible, especially a wide strip running from southwest of the centre to the north. But also to the east and northeast of the centre I can see two large empty spaces. There are two colored stars visible. To the north of the centre of M44 I see a yellow star and to the east of the centre I see a star with a yellow-orange glow. I cannot detect any other stars that show color.

I have seen this cluster through my big binoculars many times, but the view through the 4-inch refractor is the best until now.
With 158 parsecs, M44 is one of the closest open clusters as seen from the earth. When we look in the direction of M44, we look outward, away from the dusty galactic disc, into the intergalactic space. Because most open clusters lie within the spiral arms of our galaxy, at or near the galactic plane, we see only a few open clusters in this direction. Besides M44, the only other open clusters in this region are Melotte 111 (the Coma Berenice Star Cluster), M48 and M67.

M44 lies at an apparent galactic latitude of 32.6 degrees, which is almost the same for M67. Both lie almost in the same line of sight, only M67 lies five times farther out than M44, at a distance of almost 800 parsecs. This means that M67 lies about 400 parsecs of the galactic plane. while M44 lies much closer to the actual galactic plane. It only looks as if M44 lies higher from the plane, just like M67, because it is very close to us. The image below shows an edge-on view of the galactic disk with the positions of the four open clusters I mentioned above.. You see the sun marked as an orange dot and the four nearby open clusters as yellow dots. The only cluster that lies far from the galactic is M67. The other three lie very close to the galactic disk.
Stacks Image 1573

Image from "Where is M13" by thinkastronomy.com

Color magnitude diagram
While observing and sketching M44 I detected two colored stars, HD 73665 and HD 73974, both K0III red giants. According to the data in the WEBDA database, there are three other giant stars in M44. One of them is a G0III giant, HD 72779, which lies outside the field of view of the sketch. I did sketch the other two remaining giants. The first is HD 73598, again a K0III red giant, the other is HD73710, a G9III red giant. However, at the eyepiece both stars looked white to me, so I will have to revisit them, probably with a larger aperture, to detect the color.

Then there are a few blue stragglers in M44. And one of them, HD73666 an A1V dwarf star, has been studied very recently. Now what is a blue straggler? A Blue straggler is a star in an open or globular cluster that is hotter and bluer than other cluster stars having the same luminosity. Thus, it is separated from other stars on the cluster's Hertzsprung-Russell diagram. And what leads to the formation of a blue straggler?

In 2007 Ahmuda and Lapasset listed 7 frequently cited theories to explain the formation of Blue stragglers.

They could be:
  1. horizontal branch stars that appear above the main sequence turn-of point
  2. stars of the second or third generation;
  3. stars that have extended their main sequence life due to some internal mixing (this would generate a chemically peculiar blue straggler);
  4. stars formed by collision of two single stars;
  5. the result of mass transfer in a close binary system;
  6. produced by a merger of the components of a binary system;
  7. the result of a collision between two or more binary systems.

Of those seven theories they considered the last four as major channels of formation. In a study which was published in November 2009 by Fossati, Mochnacki, Landstreet and Weiss, it is concluded that HD 73666 was most likely formed by physical stellar collision of two low-mass stars. For more details on this study, please follow this link to the publication. To see the individual stars labeled in both the sketch and the color-magnitude diagram, just move the mouse pointer over the image.
The color magnitude diagram to the right was created from WEBDA dataset, Johnson H.L., Praesepe, magnitudes and colors, 1952ApJ...116..640J. With the data I created the diagram in Microsoft Excel and added the colored markings and labels with image processing software.

I selected the blue straggler and the red giants from Source: Webda, UBV color magnitude diagram of M44:

HD 73666: Blue Straggler
HD 72779: Red giant
HD 73598: Red giant
HD 73665: Red giant
HD 73974: Red giant
HD 73710: Red giant

  • Atlas of the Messier-Objects by Ronald Stoyan
  • Sky Vistas by Crossen and Rhemann
  • Sky Catalog 2000 Vol1 by Hirschfeld and Sinnott
  • Star Clusters by Archinal and Hynes
  • The Messier objects by O'Meara
  • Sterne und Sternhaufen by Payne-Gaposchkin
  • Die offenen Sternhaufen unser Galaxis by Gotz

Stacks Image 1589
Stacks Image 1590

Move mouse pointer over image to see individual stars labeled