Open Clusters

Open star clusters are so called because although the stars are organized into a group, this association is fairly loose and the stars are usually not densely packed together.  Stars often form in groups, from the same gas cloud and often some remnants of this formative cloud can be seen still associated with the cluster.

Open clusters are the most easily seen type in a small telescope or binoculars, being often rather larger than globular clusters (see the relevant page on this site).  They can be most spectacular due to the many different star colors which results from the varying stellar temperature.  It can be an amazing sight to see yellow, green,  blue and red stars all contrasting with each other in the same patch of sky.  Here are some of the better examples.

Alberio_170617_web.jpg (344289 bytes) Alberio in Cygnus.  Many star systems are multiples, and in this case the head star of the constellation of the Swan is a very fine blue and yellow double.  Full Resolution Image (2.2Mb)
Double_Cluster_14Aug2001.jpg (94959 bytes) The famous "Double Cluster"  in Perseus was known as a nebulous star to the ancient Greeks, and before them the Babylonians.  Comprising NGC 869 (upper right) and NGC 884, this super pair of clusters are rather different from each other.  NGC 869 comprises young, bright giants and supergiants, whereas NGC 884 is rather older, with mostly white and red stars
M6_220517_Web.jpg (429337 bytes) Messier 6 in Scorpius is also known as the "Butterfly Cluster".  It contains 80 stars, shines at a magnitude of 4.2 and lies ata distance of 1,300 light years.  Full Resolution Image (2.7Mb)
M7_160617_Web.jpg (342946 bytes) Messier 7  in Scorpius.  If you look just to the left of the two stars in the "Stinger" of the Scorpion you will see a bright patch.  In a picture this is what you see - millions of stars, with the hot, blue stars of M7 superimposed.  This black and white image was shot late in the evening as Scorpius was fast disappearing.  There are so many stars here, it is difficult to know what you are looking at.  Full Resolution Image (1.9Mb)
M11_170617_Web.jpg (643534 bytes) Messier 11 in Scutum is an extremely rich open cluster at a distance of about 6,200 light years.  It is so rich with stars that it has been mistaken for a loose globular cluster.  About 250 million years old, M11 is very luminous, with several dozen members and a luminosity of about 48,000 of our suns.  Full Resolution Image (2.7Mb)
M18_170617_Web.jpg (586685 bytes) Messier 18 in Sagittarius was discovered by Messier on 3rd June 1764.  It is a little below M17 and surrounded by slight nebulosity.  About 4,100 light years distant it shines with the light of 8,300 suns.  Full Resolution Image (3.1Mb)
M21_160617_Web.jpg (545389 bytes) Messier 21 in Sagittarius was discovered by Messier in June 1764 while he was observing the Trifid nebula.  5,200 light years distant, it has a diameter of 20 light years and shines with the radiance of 20,000 suns.  Full Resolution Image (3.0Mb)
M23_160617_Web.jpg (427538 bytes) Messier 23 also in Sagittarius and also discovered by Messier in June 1764 it actually covers an area as large as the full moon, is 2,100 light years distant and has a luminosity of 6,300 suns.  Full Resolution Image (2.7Mb)
M24_210607_Web.jpg (279972 bytes) Messier 24 in Sagittarius is actually called the Small Sagittarius Star Cloud, but Messier chose to add this huge area to his list of comet "look-alikes" in 1764.  The star cluster in the centre is NGC 6603 and it is a beautiful sight in a telescope. This is an LRGB of 10:10:10:10 minutes with the Takahashi FSQ scope and ST8-XE camera, taken in Spain on 21st June, 2007
M25_170617_Web.jpg (401236 bytes) Messier 25 in Sagittarius is actually visible to the naked eye in dark skies.  Discovered by de Cheseaux in 1746 the cluster is about 3,000 light years distant and shines with the luminosity of 33,000 suns.  Full Resolution Image (2.2Mb)
M26_170617_Web.jpg (548081 bytes) Messier 26 in Scutum is a rich 5 arc minute diameter of 2 dozen 11th to 13th magnitude stars, standing out against the background of the Milky Way.  Full Resolution Image (2.7Mb).
M29_151116_1200.jpg (1296533 bytes) Messier 29 in the constellation of Cygnus is a fairly small open cluster, discovered by Messier himself in 1764.  Messier's description mentions "7 or 8 very small stars" but because these brightest members of the clusters are blue giants, the cluster shines with a luminosity equivalent to 160,000 of our suns.  The cluster is 11 light years in diameter and is 6,000 light years from us.  This image was taken on 15th November, 2016 using the Planewave scope and QSI camera. It is an LRGB of 5 minutes per component.  Full Resolution Image (2.8Mb)
M34_18Nov2001.jpg (48440 bytes) Messier 34 in the constellation of Perseus is a large, attractive open cluster of stars which looks fine in smaller telescopes.  Discovered by Messier in 1764, this relatively young cluster is approximately 180 million years old and is about 1,500 light years distant.  Containing about 80 stars, it is interesting to note how the stars are arranged in chains, with seven at 8th magnitude and two dozen of 9th and 10th magnitude
M35_191001_Web.jpg (162739 bytes) Messier 35 in Gemini.  A fascinating image, this shows the bright open cluster, M35 which was recorded by Messier in 1764, but had already been catalogued by Swiss astronomer de Chesaux in 1745.  About 2,200 light years away it is a magnificent cluster with 150 stars of 8th magnitude or less in a 1.5 degree field.  Even more fascinating is the faint open cluster NGC 2158 in the top left corner.  This little cluster is much more remote, on the outer edges of one of the spiral arms of our galaxy.  The image is an LRGB of 20:5:5:5 minutes at f/5. Full Resolution Image (0.6Mb)
M36_19Oct2001.jpg (62007 bytes) Messier 36 in the constellation of Auriga the Charioteer, and one of the three Messier open clusters in this constellation, was actually discovered in 1749 by Le Gentil.  The cluster is 14 light years across and approximately 4,100 light years distant, ten times the distance of the famous Pleiades cluster.   Because it is actually three times brighter than the Pleiades, if it were at the same distance it would be the brightest open cluster in the sky.  This image is an LRGB of 20:5:5:5 minutes taken at f/5
M37_181101_Web.jpg (157016 bytes) Messier 37 in Auriga.  One of my favourite open clusters in the sky, and similar in many ways to M11 in Scutum, this cluster is older and more evolved than the other clusters in Auriga.  With at least 150 stars of magnitude 9 through 12.5 it shines with the light of 2,500 suns and is 25 light years in diameter.  Messier also discovered this cluster in 1764, one of his more productive years.  Full Resolution Image (0.6Mb)
M38_20Dec2001.jpg (90196 bytes) Messier 38 in Auriga is a large, irregular and rather scattered group of stars.  The cluster, which was discovered in 1749 by Le Gentil, has a diameter of 25 light years - about the same as for M37, and its brightest star is a yellow G0 giant, which is about 900 times brighter than our sun
M39_190617_Web.jpg (454241 bytes) Messier 39 is an open cluster in the constellation of Cygnus.  This is a poor, sparse open cluster, first discovered by Le Gentil in 1750, but only added to Messier's list in 1764.  It is 830 light years away, with a diameter of about 7.5 light years.  Full Resolution Image (2.8Mb)
M41_20Dec2001.jpg (83590 bytes) Messier 41 is in Canis Major, not far from Sirius, the brightest star in the northern sky.  This is a large, bright cluster, even visible to the naked eye on dark nights.  In wide field eyepieces or binoculars it looks superb, and at its distance of 2,350 light years it shines very brightly, with a luminosity of 8,000 of our suns
M44_20Dec2001.jpg (44522 bytes) Messier 44 in Cancer is commonly known as the "Beehive" cluster.  It was known in Biblical times, which gave rise to its other name of "Praesepe", which means "the Manger.  One of the largest and brightest of open clusters, it is only 525 light years distant, but its stars are quite old, at around 700 million years
M46_201201_Web.jpg (139856 bytes) Messier 46 at the top end of the constellation of Puppis is one of my favourite objects.  Discovered by Messier himself in 1771,  M46 has fainter stars than its neighbour, M47 but they are more dense, and the cluster is further enhanced by a beautiful little planetary nebula (lower left) - NGC 2438.  This planetary is not associated with the cluster, but is a foreground object, much closer to us than the stars of the cluster itself.  Full Resolution Image (0.6Mb)
M47_23Dec2001.jpg (65760 bytes) Messier 47 also in Puppis is an extremely large and bright open cluster, visible to the naked eye as a hazy patch, and partially resolved in binoculars.  M47 is very young - about 25 to 30 million years old - and is 1,700 light years distant.  It has a diameter of about 15 light years
M48_23Dec2001.jpg (59966 bytes) Messier 48 is one of those objects which was described by Messier, but not located at the position he noted.  It is assumed that he made a mistake, and NGC 2548, which is four degrees south of where Messier described, is generally accepted to be M48.  It is a bright open cluster, 1,500 light years away and 24 light years in diameter
M50_20Dec2001.jpg (73142 bytes) Messier 50 in Monoceros is a fine open cluster first discovered by Cassini around 1711, but had to be re-discovered by Messier in 1772.  M50 is 2,900 light years away, 14 light ywars in diameter, and has a luminosity of 6,400 of our suns
M52_18Oct2001.jpg (100314 bytes) Messier 52 an open cluster in Cygnus.  Discovered by Messier in 1774, M52 is 3,900 light years away and is about 15 light years in diameter.  It is a very dense, rich and compressed cluster, containing a number of blue-white B3 main sequence stars.  From this information we can estimate the age of the cluster as about 50 million years, so it is a very young cluster in one of the spiral arms of our Milky Way galaxy.  This image is an LRGB of 20:10:10:10 minutes at f/5
M67_23Dec2001.jpg (32315 bytes) Messier 67 in Cancer is one of the most ancient open clusters known, at 5 billion years old.  Most open clusters are distributed along or close to the plane of our Milky Way galaxy's spiral disc, but M67 has been able to work its way outwards to its current position 1,500 light years out of the galactic plane.  It is 2,600 light years from us, 12 light years in diameter and has about 500 member stars 
M93_23 Dec 2001.jpg (73701 bytes) Messier 93 in Puppis is a thinly populated open cluster discovered by Messier in 1781.  It lies at a distance of 3,400 light years, has a diameter of 20 light years and has a luminosity of about 4,000 of our suns
M103_20Dec2001.jpg (76149 bytes) Messier 103 in Cassiopeia is an open cluster discovered by Mechain in 1781.  The area immediately surrounding this cluster is rich with open clusters, double stars and other interesting objects.  M103 lies 9,200 light years away and is about 15 light years in diameter
N457_100913_Web.jpg (334807 bytes) NGC 457 in Cassiopeia is a favourite cluster with young people.  It is sometimes called the "ET" cluster because the two bright stars look like eyes and the body, arms and legs can also be seen.  It's a bit difficult to show this in an image because many more stars are visible than with the naked eye and it muddles it a bit.  This is an LRGB of 6 minutes for each component taken with the Planewave and QS683 on 10th September, 2013.  Full Resolution Image (8Mb) or a smaller high res image
NGC2264_22Dec2001.jpg (101349 bytes) NGC 2264 commonly known as the "Christmas Tree" cluster is located in the constellation of Monoceros.  To see the tree it is necessary to view the image lying on your side (sorry for this).  The stars of this cluster are embedded in an extensive but tenuous nebulosity and traces of this can be seen "trimming" the tree.  The dark, "Cone nebula" can be seen at the "top" of the tree to the right of the image
N6645_180916_Web.jpg (388907 bytes) NGC 6645 in Sagittarius. This is a rich open cluster of seventy 11th to 14th magnitude stars set against the background of a rich area of the Milky Way galaxy. This image is an LRGB of 10 minutes for each component, taken in Spain on 18th September, 2016 using the Planewave telescope and QSI 683 camera. Full Resolution Image (7.1Mb). Smaller high res image (1.5Mb)
N6355-Region_220612_Web.jpg (437932 bytes) The Region Around GC 6355 and the edges of the Pipe Nebula in Ophiuchus.  Imaged in Spain on 22nd June, 2012 using the Takahashi FSQ 106 4 inch refractor and ST10 XME camera.  This is an LRGB or 30 minutes for each component and it was a "first light" image for the ST10 on the little Takahashi.  Full Resolution Image (3.2Mb)
Roslund4_271016_1200.jpg (1673129 bytes) Roslund 4 in Sagitta.  This cluster is partially embedded in nebulosity and is 8,655 light years distant from us.  Full Resolution Image (13Mb). Smaller high res image (1.6Mb)

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