Stockton Astronomical Society
Valley Skies - February 2000 Issue
Constellations:
Monoceros The Unicorn
Gen: Monocerotis
Abb: Mon
Dec: -11.0° to +11.9°
RA: 5h 54m to 8h 8m
Area Covered: 482 square degrees
Monoceros means unicorn from the Latinized version of the Greek word "monokeras" which means single horn. Monoceros is a very young constellation of uncertain origin. Most sources state that this constellation was given its name by Jakob Bartsch, some time around 1624, but I have also found record of its name being used many years earlier by the Dutch astronomer Petrus Plancius. In books that were written during the middle of the 1500s there are passages that talk about a horse in this area of the sky. Monoceros may have been part of some other constellation whose name and description that did not survive into modern times.
Since the Unicorn myths are from Europe's Middle Ages, I am sure that the constellation was viewed as a unicorn, then its name changed to the Latin form to fit in with the rest of the constellation names. As I stated above all references to unicorns come out of the Middle Ages. I have read many stories growing up and several more recently (both for this article and because I have a young daughter who adores Unicorns, as most young girls do) looking for any association with this group of stars. I was unable to find any connection, so I apologize to those of you who read this article for the mythology part. Maybe we will have a good one for next month.
Monoceros is very faint and hard to pick out. It reaches its highest point in the sky at 10:00pm on the 1st of February. None of the stars in Monoceros are brighter than fourth magnitude so you need to look in the area outlined by Procyon, in Canis Minor; Sirius, in Canis Major; and Betelgeuse, in Orion. If you have a very dark site you may pick it out weaving through this area, but it easily gets lost in the Milky Way that passes through this section of the sky. Since this constellation is so hard to find we will start our hops in Canis Major.
Exploring in Monoceros
Monoceros has several open clusters located within its boundaries and a few patches of nebulosity. There are no globular clusters in Monoceros, so all the clusters mentioned in this article are open clusters.
Start at Sirius--this is the brightest star in the sky, located to the southeast of Orion. From Sirius hop 9° northeast (this is just under the width of your clenched fist) to find our first cluster of the night NGC 2323 (M-50). NGC 2323 is visible in most finder scopes (40mm and larger) as a tight knot of stars that stands out from the surrounding star fields. It was first located by the Italian astronomer Giovanni Domenico Cassini (father of Jean Dominique Cassini, discoverer of the gap in Saturn's rings) sometime prior to 1711. Messier did not find this cluster until April 5th 1772 while looking for the comet of 1772. In a telescope, M-50 consists of about 80 stars that range in brightness from 12th to 16th magnitude, loosely packed into a large group. The combined light from all the stars in this cluster is listed as 5.9 magnitude in my books. If you go to a low power at this point you can follow a trail of 9th and 10th magnitude stars 2° to the southeast to get NGC 2335, 2343 and possibly NGC 2353 in your finder scope.
These three clusters form a triangle with NGC 2335 at the northernmost point, NGC 2343 to the south and NGC 2353 about 1½° to the east. NGC 2343 is the brightest of the trio at magnitude 6.7 and would be the easiest one to find if it wasn't so loose that it blends in with the rest of the surrounding stars. NGC 2335 is the faintest member but it is a tighter cluster, containing 30 to 35 stars. You can pick out NGC 2353 by looking for the cluster that has one star that is much brighter than all the other stars in the cluster.
Return to M-50. At this point if you have a big scope, you can try for NGC 2311 located just over 4° to the north-northwest. This cluster is listed as "50 stars, weak concentration, photographic magnitude 9.6". I tried to find a visual magnitude or at least some information I could use to get close but I didn't have any luck. To those of you who try for it, good luck, and I will be giving it another shot at the next star party.
From NGC 2311 travel about 5½° northeast, or from M-50 just over 8° north-northeast, to Delta Monocerotis. Delta is shown as a double star on my charts but I didn't find any information on it or it's companion. From Delta head 2¾° northwest to find NGC 2324, a faint (8.4 magnitude) but fairly rich cluster of about 70 stars. This is also one of the oldest clusters in the area with an estimated age of 660 million years. Continue on the same distance (2¾°) just to the south of west to hit NGC 2301. This cluster is a lot easier to hit than 2324. In fact, at mag. 6 you should be able to see it clearly in your finder scope or binoculars. NGC 2301 is a rather large, rich cluster of about 70 to 80 stars with a strong central concentration.
Just under 4° south-southwest of NGC 2301 is NGC 2286. This cluster is very hard to pick out of the stars along the Milky Way. It is pretty large and the individual stars vary in brightness by so much that they appear as just another star field.
Our next stop is Beta Monocerotis, located 6° to the southwest of NGC 2286. Beta is a beautiful quadruple star system and has long been a favorite of amateur astronomers that observe multiple stars. Even 60mm scopes will be able to separate the three stars Beta A, B and C with little or no problem but it will take a larger scope to locate the fourth star. The fourth star is a 12th magnitude star located 27" from the A star.
These next two clusters are not all that great -- in fact the only reason that I even mention them is because they show up on the star chart. The first one, NGC 2215, is located 2° west of Beta and consists of about 30 very detached stars. Next head 3½° north-northeast to the area north of Beta to find NGC 2232. Even though this cluster is listed as 20 stars and magnitude 3.9, I only counted 9 stars, including 10 Monocerotis that clearly stood out of the surrounding stars.
The next hop is a long one, just under 10° to the north then 1° to the east. At a dark site you can make out two naked eye visible patches of light in this area. Our first target is the southernmost patch of light. The light is coming from two open clusters, NGCs 2239 and 2244. These clusters are surrounded by three emission nebulas, NGC 2237, NGC 2238 and NGC 2246. All of these objects together form the "Rosette Nebula". It takes a very large scope or a long exposure photograph to really bring out the nebula's intricate details. In pictures the nebula's red color adds to the appearance of rose petals opening around the young stars clustered in its center. Pictures from the Hubble Space Telescope show a lack of dust and gasses in the center and it is believed that it has been used up in the forming of the cluster; the very hot young stars then provide the light and energy that allows us to see the nebula.
From the Rosette Nebula continue north-northeast to the next patch of light. The light is coming from NGC 2264 and is also known as the "Christmas Tree Cluster". This cluster is magnitude 3.9 and looks like a lighted Christmas tree hanging upside down. The cluster sits in a huge area of nebulosity but I can not pick out any trace of it in my 10-inch scope. Hopefully when Jeff gets his 40 inch on line we may be able to see the nebulosity and the "Cone Nebula", which is a dark nebula that protrudes into the area at the top of the tree.
Before going to this last hit I want to warn you first so that you don't go racing down the hill or tear your car apart to find your cellular phone! Even though it looks like a comet it is really a nebula.
From the Christmas tree drop down just over 1° south-southwest to find NGC 2261. NGC 2261 is Hubble's Variable Nebula; it's an emission nebula that looks very much like a comet. The nebula has what appears to be a bright nucleus and a broad fan shaped tail. The nebula is illuminated by the star "R Monocerotis," which looks like the nucleus of the comet. R Monocerotis is a variable star that changes in brightness over a rather short period of time; it also has a cloud of dust and gasses that are moving very close to it. These two factors cause the nebula itself to change dramatically in brightness and appearance in just a few months.
There are a few more open clusters in this constellation, and the last two areas deserve a fair amount of investigation. I hope I have given you a good start to work from as you explore the winter section of the Milky Way.
Happy Star Hopping...Eric
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Lasted Updated: 12/27/2000
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