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One classification of open clusters is the Trumpler classification. It consists of 3 parameters, the first is the degree of concentration.

I - Detached clusters with strong central concentration.
II - Detached clusters with little central concentration.
III - Detached cluster with no noticeable concentration.
IV - Clusters not well detached, but has a strong field concentration.

The second parameter is the range of brightness.

1 - Most of the cluster stars are nearly the same apparent brightness.
2 - A medium range of brightness between the stars in the cluster.
3 - Cluster is composed of bright and faint stars.

The last parameter categorizes the number of stars in the cluster.

p - Poor clusters with less than 50 stars.
m - Medium rich cluster with 50-100 stars.
r - Rich clusters with over 100 stars.

If the cluster any type of nebulosity, the letter "n" is added to the last parameter.

 


First up is Messier 34, located in the constellation of Perseus. Consisting of over 100 stars, in a space of a diameter of 14 light years. It is some 1,500 light years distance and shines at an apparent magnitude of 5.5 at an estimated age of 200 million years.

Telescope: GSO RC10
Camera: ZWO 2600 MM
Constellation: Canis Major
Right Ascension: 06h 46.0m
Declination: −20° 46′
Distance: 2,300 ly
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Messier 41 is an open cluster located in Canis Major near Sirius. The cluster contains some 100 members in a diameter of 25 light years. Estimated age of the cluster is around 200 million years. It is expected to remain as a cluster for 500 million years before dispersing. Brightest of the stars is an orange giant near the cent of the cluster. K3 type star, it has a magnitude of 6.3 and is 700 times more luminous than our Sun.

Telescope: Explore Scientific 127 Refractor
Camera: ZWO 2600 MM
Constellation: Taurus
Right Ascension: 03h 47m 24s
Declination: +24° 07′ 00″
Distance: 444 ly
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Messier 45, one of the more famous open clusters. Often called the Pleiades or the Seven Sisters, with the name Pleiades coming from Greek mythology. The cluster has been known since ancient times, and can be seen as a grouping of 6-7 stars, so it was interesting that Charles Messier included it in his catalog of objects that are not a comet, but could be mistaken for one.

The cluster is surrounded by a reflection nebula that the group is currently passing through, and not related to its original birth in a compact nebula. The cluster consist of at least 1,000 stars located in a radius of 8 light years. The cluster is dominated by hot blue luminous stars, but also contains many brown dwarfs that are not massive enough to initiate nuclear fusion. The estimated age of the cluster is around 100 million years, and its expected to take 250 million years to disperse due to gravitational interactions.

Telescope: Explore Scientific 127 Refractor
Camera: ZWO 2600 MM
Constellation: Cassiopeia
Right Ascension: 01h 19m 32.6s
Declination: +58° 17′ 27″
Distance: 7,900
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NGC 457 is an open cluster located in Cassiopeia, often called the Owl cluster, or a more recently the E.T. cluster with the two brightest stars forming eyes. I tend to see it more as an Owl. The cluster contains some 150 members and has an estimated age of around 21 million years. Less than idea weather for imaging, with a thin cirrus clouds, but a good bright target for commissioning the RC 10 scope and the ZWO 2600 mono camera.

Telescope: GSO RC10
Camera: ZWO 2600 MM
Constellation: Cassiopeia
Right Ascension: 23h 58m 24.2s
Declination: +61° 12′ 30″
Distance: 10,800 ly
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NGC 7790, center of image is a young open cluster located in Cassiopeia with an estimated age of 60 to 80 million years. Open cluster NGC 7788 lies to the lower left of NGC 7790

Telescope: Explore Scientific 127 Refractor
Camera: ZWO 2600 MM
Constellation: Cassiopeia
Right Ascension: 01h 33.2m
Declination: +60°42′
Distance: 10,000 ly
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Messier 103 is an ope star cluster located in Cassiopeia. Contains at least 107 members, its one of the smallest and at 10,000 light years one of the more remote clusters.

Telescope: Explore Scientific 127 Refractor
Camera: ZWO 2600 MM