Skip to Navigation | Skip to Content

Previous image Up to Astr111 Index Next image ASTR 110 Photography Projects, Fall 2016

M15, M92 & NGC 189
Kyle Klaver, Chloe Keller & Emily Franks

M15 M92
M15 Star Cluster- Kyle Klaver M92 Star Cluster- Chloe Keller

NGC 189
NGC 189 Star Cluster- Emily Franks  

The three star clusters discussed on this page are M15, M92, and NGC 189. A star cluster is “a number of stars of common origin held together as a group by gravitational attraction.” ( Stars are typically born into clusters, either globular or open. Globular clusters tend to be dense and old, as each star’s gravity prevents the migration of the rest of the stars. Open clusters, on the other hand, tend to be young and disperse, as the fewer number of stars lack enough gravity hold each other close together (Bennett et. al, 2010). M15 and M92 are both globular clusters, making them packed with multitudes of brilliant stars. NGC 189 is an open cluster which is why it looks more dispersed and less prominent.

Messier 15, also known as M15, is a globular star cluster. It was discovered in 1746 by Jean-Dominique Maraldi. A globular star cluster is group of stars that are gravitationally bound and contain from around 10 thousand to a million stars. They can be spread over tens of lightyears up to around 200 lightyears ("Globular Star Clusters"). M15 has over a hundred thousand stars and is approximately 175 lightyears in diameter. M15 is a little less than 34 thousand lightyears from Earth, so it is still in our Milky Way galaxy. Within the Milky Way, it is one of the most densely packed clusters known. It is also one of the oldest clusters discovered, with an estimated age of 12 billion years. M15 has a total luminosity of over 360 thousand times that of the Sun. M15 also contains over a hundred variable stars and several pulsars ("Messier 15").

M92, or Messier 92, is a globular cluster that falls in the constellation Hercules; specifically, the cluster is centered between the constellation’s “arms”. This globular cluster was first discovered by Johann Elert Bode in 1777, but was named after Charles Messier who rediscovered the cluster in 1781. M92’s spatial diameter measures at 108 lightyears (Peterson). As for distance from Earth, M92 is “about 26,700 light-years away… [and] is among the brighter clusters in terms of absolute magnitude.” Additionally is one of the oldest clusters in the Milky Way (Wikipedia).

Not much is known about open star cluster NGC 189 located in the Cassiopeia constellation. It was found in September of 1783 by Caroline Herschel. The observation of this cluster was confused with another cluster, NGC 381, and 46 years later it was rediscovered by John Herschel and called H 36. In 2005, it was realized that they were the same object. (Kronberg) NGC 189 is approximately 3,500 light years away from Earth. It has a brightness magnitude of 8.8, so it is visible with binoculars, but not to the naked eye. It has a right ascension of 0h 39m and 35s and a declination of 61* 05’ 42”. (DSO Browser)

M15 and M92 and much more similar to each other than NGC 189 as they are both globular clusters and NGC 189 is an open cluster. Therefore, M15 and M92 have a much larger quantity of stars and have much higher total luminocities. M15 and M92 have similar apparent brightnesses. NGC 189 has a smaller total apparent brightness but some of its stars have similar apparent brightnesses to stars in the globular clusters. M15 and M92 both have similar structures because they have so many stars that the gravity is strong enough to hold them together.

There on many differences between M15, M92, and NGC 189. One of the most prominent being that M15 and M92 are globular star clusters and NGC 189 is an open star cluster, there are many differences that occur just because of this reason. M15 and M92 are both older than NGC 189. Of the three clusters, NGC 189 is the closest to Earth, even though M15 appears to be the brightest of the three. Other differences include that NGC 189 has significantly fewer stars in the cluster, on account that it is an open cluster, whereas M15 and M92 are both globular clusters. Another difference between the three is that NGC 189 has less of a gravitational pull on it than the other two.


Bennett, Jeffrey, Megan Donahue, Nicholas Schneider, and Mark VoitThe Cosmic Perspective: Fundamentals. San Fransciso: Pearson Addison-Wesley, 2010. Print.

Kronberg, Hartmut Frommert Christine. "NGC 189." NGC 189. N.p., n.d. Web. 30 Nov. 2016.

McArthur, Guy, Hartmut Frommert, and Christine Kronberg. "Globular Star Clusters." The Messier          Catalog. SEDS USA, 10 July 2014. Web. 21 Nov. 2016. <>.

McArthur, Guy, Hartmut Frommert, and Christine Kronberg. "Messier 15." The Messier Catalog. SEDS       USA, 19 Feb. 2014. Web. 21 Nov. 2016. <>.

"Messier 15." Wikipedia. Wikimedia Foundation, 15 Nov. 2016. Web. 21 Nov. 2016.                 <>.

"Messier 92." Wikipedia. Wikimedia Foundation. Web. 27 Nov. 2016.

"Open Cluster NGC 189 · Deep Sky Objects Browser." DSO Browser. N.p., n.d. Web. 30 Nov. 2016.

Peterson, Andy. "Messier 92 - M92 - Globular Cluster.Free Star Charts. Web. 27 Nov. 2016.

"Star Cluster." Web. 27 Nov. 2016.

Object M15 Star Cluster M92 Star Cluster NGC189 Star Cluster
Right Ascension (J2000) 21:29:58 17:17:07 00:39:06
Declination (J2000) +12:10:01 +43:08:09 +61:04
Filters used B (Blue), R (Red), V (Green) B (Blue), R (Red), V (Green) B (Blue), R (Red), V (Green)
Exposure time per filter B (150s); V and R (60s) B, V, and R (180s) V and R (200s); B (300s x 2)
Image dimension 741x694 pixels; 16.1x15.0 arcminutes 1092x736 pixels; 23.8x16.1 arcminutes

775x533 pixels; 16.8x11.5 arcminutes

Date/time observed October 7, 2016, 7:16 UT October 7, 2016, 4:07 UT October 4, 2016, 9:20 UT


Secondary content.


Side content.