the Stargazers’ Newsletter Janurary 2002 Volume II,  Number 1 Robert Young, Ed.D. Web Master: Jeff Hargett

Feature Article:   
Open Clusters

As a class of objects, open clusters are quite pleasing and enjoyable to view. The question is "What is an open cluster?"

Open clusters are physically related groups of stars held together by mutual gravitational attraction. Open clusters consist of stars about the same age, they are about the same distance away from us, they have the same chemical composition, and they have the same proper motion. They are believed to originate from large cosmic gas and dust clouds (diffuse nebulae) in the Milky Way and they continue to orbit the galaxy through the disk. In many bright nebulae, star formation takes still place at this moment and we can observe the formation of new young star clusters. A good example of this is in the Eagle Nebula M16 (NGC 6611) in Serpens.
http://antwrp.gsfc.nasa.gov/apod/ap970118.html
http://antwrp.gsfc.nasa.gov/apod/ap000924.html

It is estimated that there are between 1,100 and 1,200 open clusters with most of them being confined to the Milky Way band. Virtually, regardless of your viewing location or your telescope aperture, you will be able to see several wonderful open star clusters on clear nights. How well a cluster shows up in your telescope or binoculars depend on the size of the cluster, magnitude of the stars in the cluster, and the number of stars in the cluster. Large open clusters require low magnification. It is best to see an open cluster when the eyepiece field of view is twice the diameter of the cluster. This makes it easier to see the open cluster framed against the star field background. Although it would seem that though it would be, star magnitude is not necessarily a good indicator of how easy it is to see an open cluster. When star magnitude for an open cluster is reported, it represents the cluster's total brightness including all of the member stars. So two clusters having equal magnitude, one with several hundred dim stars would be more pronounced in a telescope than one with just a few bright stars.

Most open clusters have only a short life as stellar swarms. As they drift along their orbits around the galaxy, some of their members escape the cluster, due to encounters with the gravitational fields of other clusters or objects crossing their way. As such, most open clusters are relatively young in that they spread most of their member stars along their orbital path after several 100 million years; only few of them have an age counted by billions of years. The escaped individual stars continue to orbit the Galaxy on their own as field stars.

The most prominent examples of the earliest known open clusters include:
- the Pleiades (M45) http://antwrp.gsfc.nasa.gov/apod/ap000227.html ,
- the Hyades http://antwrp.gsfc.nasa.gov/apod/ap000929.html
- and the Beehive or Praesepe (M44) http://antwrp.gsfc.nasa.gov/apod/ap980803.html .

Ptolemy had also mentioned M7 http://antwrp.gsfc.nasa.gov/apod/ap000405.html and the Coma Star Cluster (Mel 111) as early as 138 AD. First thought to be nebulae, it was Galileo who in 1609 discovered that they are composed of stars, when observing M44.

Open Clusters are categorized by their appearance. An important classification scheme introduced by R.J. Trumpler in 1930 consists of three parts, characterizing the cluster's degree of concentration, the range of brightness of its stars, and the richness:

Concentration
I Detached; strong concentration toward center
II Detached; weak concentration toward center
III Detached; no concentration toward center
IV Not well detached from surrounding star field

Range in Brightness
1 Small range in brightness
2 Moderate range in brightness
3 Large range in brightness

Richness
(p)  Poor: Less than 50 stars
(m) Moderately rich: 50 to 100 stars
(r)   Rich: More than 100 stars

It is not always immediately apparent when you are looking at an open cluster. The closer a cluster is to us the more spread out it is - the less concentrated the cluster the more difficult it is to see through a telescope. It is like driving in a light fog and only seeing a light mist. But after driving away some distance from the fog and looking back, you see what looks like a dense well-defined cloud. Open clusters are like this. Some open clusters are really quite difficult to see even when you know exactly where to look - for me NGC 7686 in Andromeda is just such an open cluster. This is truly a "I can't see the forest for the trees phenomenon."

The secret to seeing open clusters is to first us a wide-angle, low magnification eyepiece and then work your way to greater magnification.

When you go out observing this month, pay particular attention to the open clusters.

Featured Constellation:
Camelopardalis (ka-mel-o-PAR-da-lis)
The Giraffel

http://www.dibonsmith.com/cam_con.htm

Camelopardalis is described as being a modern constellation. Bartsch dreamed up this constellation in 1624, claiming that it represented the camel that brought Rebecca to Isaac. The Greek name for giraffe is "Camel-Leopard" as they thought it had the head of a camel and the spots of a leopard. This constellation occupies a rather large, faint region centered between Ursa Major, Cassiopeia, Perseus, Auriga, and Polaris (the North Star). Although Camelopardalis is among the larger constellations, its brightest stars are only of the 4th and 5th magnitudes. According to the National Audubon Society Field Guide to the Night Sky, "to find the brightest stars, look at the constellation's southern end, in the area bounded by Cassiopeia, Perseus, and Auriga. The rest of the group straggles toward the north celestial pole, ending with some very faint stars just above the curve in the handle of the Little Dipper" (page 452).

Planet Watch

Once again we have a chance to see Mercury as it zooms around the Sun. Early in the evening, just at sunset, look low in the west. From the first of January to the 11th it will be increasing it height above the sunset horizon and its brightness. On the 11th of January it will be at its greatest elongation and will be 19 degrees above the horizon at a magnitude of -0.1. Look quick because by January 19th it will have slipped back into the sunset glare. Venus is behind the Sun this month and will be in superior conjunction on the 14th (meaning that the Earth and Venus are on exactly opposite sides of the Sun).

Mars is continuing to slip to the west as the days and weeks pass. Mars in not overly bright now (mag +1) but is much brighter that the background stars of Pisces. Mars will set around 10:00 p.m. each evening.

Saturn is the next planet in the procession and it shows its splendor early in the evening. You will find it in the Hyades Cluster in Taurus the Bull, just about overhead around 9:00 p.m. during the month. The rings of Saturn are about as tilted as they ever get so you need to give it a good look.

Jupiter is in opposition (meaning the Sun and Jupiter are exactly on opposite sides of the Earth) January 1st so it will be visible the whole night, rising at sunset and setting at sunrise. It is easily the brightest object in the night sky at mag -2.7 in Gemini. Take some time to check out the Galilean moons as they whirl around Jupiter.

Uranus and Neptune are all lost in the evening twilight while Pluto is lost in the Morning twilight.

Moon Watch

Dates for the phases of the moon:

Janurary 6 @ 3:55 UT - Last Quarter
              Janurary 13 @ 13:29 UT - New Moon
                            Janurary 21 @ 17:46 UT - First Quarter
                                          Janurary 28 @ 22:50 UT - Full Moon         

To see the current phase of the moon, click on this website:  http://tycho.usno.navy.mil/vphase.html

Lunar Objects of Interest

The moon makes for an interesting study because different lunar features become evident as the moon progresses through its 28-day cycle. The terminator, the shadow's edge across the moon, provides observers a chance to see vertical profiles of the moon's surface that are otherwise invisible. Thus, each day of the 28-day cycle reveals new lunar features to examine. The following website will assist you in locating this month's "Lunar Objects of Interest."

To find a picture and location of each object on our list go to the attached website, it will assist you in locating the object on the Moon. http://www.lpi.usra.edu/research/lunar_orbiter/

Looking to the northeast corner of the Moon you will find the following features:

Montes Alpes - A large mountain range running northwest to southeast.
Crater Plato - A large crater to the nouthwest in the mountain range Montes Alpes.
Vallis Alpes - A very distinct straight valley cutting across Montes Alpes and running northeast to southwest.
Mare Frigoris - The thin plateau area just north of Montes Alpes running parallel with the mountain range.
Crater Cassini - This crater is approximately four crater diameters southeast of Crater Plato and just south of the mountain range.

To find a picture and location of each object on our list go to the this website, it will assist you in locating the object on the Moon. http://www.lpi.usra.edu/research/lunar_orbiter

Messier Objects: (new feature)
Charles Messier, in the 17 century, was a comet hunter. He spent his time looking for and charting comets. Not only did he chart comets, he also charted "comet-like" objects that proved not to be comets. He listed and charted about 110 of these "comet-like" objects for other observers to avoid.

Today, the Messier List is one of the premier deep-sky object lists for amateur astronomers around the world. The list certainly does not include comets, but it does chart star clusters, nebulas, galaxies, globular clusters and even a binary pair.

Over the course of the next 12 months we will identify all 110 Messier objects. The Messier objects selected for each month will be close to the meridian at 9:00 p.m. standard time. Admittedly, as the year proceeds you will be looking deeper and deeper into the western sky for your objects. That is because I am trying to distribute the 110 objects equally over the 12 months and they are not spread equally according to right ascension.

Alert : Do not be disappointed if what you see through your binoculars or telescope do not look exactly like the pictures below. Time-lapsed photos pick up resolution and color that your eyes are unable to detect.

Monthly Messier Objects: (there may be some duplication with the Monthly Observing List).

These Messier objects were selected because of their locality in the night sky. You will look generally in a south to southwesterly direction to spot these objects in the early evening. They are in order of their right ascension.

M79 Globular Cluster, magnitude 7.9 in Lepus
http://www.fys.ruu.nl/%7Ezagers/messier/m79.html

M38 Open Cluster, magnitude 6.4 in Auriga
http://www.fys.ruu.nl/%7Ezagers/messier/m38.html

M1 Nebula (Nova Remnant), magnitude 8.0 in Taurus
http://www.fys.ruu.nl/%7Ezagers/messier/m1.html

M42 Nebula / Open Cluster, magnitude 5.0 in Orion
http://www.fys.ruu.nl/%7Ezagers/messier/m42.html

M43 Nebula, magnitude 7.0 in Orion
http://www.fys.ruu.nl/%7Ezagers/messier/m43.html

M36 Open Cluster, magnitude 6.0 in Auriga
http://www.fys.ruu.nl/%7Ezagers/messier/m36.html

M78 Nebula, magnitude 8.0 in Orion
http://www.fys.ruu.nl/%7Ezagers/messier/m78.html

M37 Open Cluster, magnitude 5.6 in Auriga
http://www.fys.ruu.nl/%7Ezagers/messier/m37.html

M35 Open Cluster, magnitude 5.1 in Gemini
http://www.fys.ruu.nl/%7Ezagers/messier/m35.html

By the Way:

If you get a chance, check out View Point in December's issue of Sky & Telescope on page 10. You may recognize the author of the article… Let me know what you think about the article.

Suggestions Corner:

Please, let me hear from you…….

If you have a topic you want covered in one of our issues please let us know. If you want to write an article to be included in this publication, either send us a copy of your article or a summary of the topic you want to write about. Our committee will give your request serious consideration and a rapid response.

Crystal Skies,

Bob
StrGazrBob@aol.com