Stockton Astronomical Society
Valley Skies - May 1999 Issue
Constellations:
Ursa Major, The Great Bear
Gen: Ursae Majoris
Abb: UMa
For this month I will concentrate on the familiar asterism known as the Big Dipper. It is important to note that the Big Dipper is a group of stars (asterism) that make up only a small part of the constellation Ursa Major that we see on star charts today. The Greeks gave Ursa Major its name about 900 years BC, and the dipper made up the body of a giant bear. Before the Greeks, it was the stars of the dipper itself that were viewed as many other objects.
The early Egyptians saw the stars as a hippopotamus. As their culture and religions grew, the stars began to be depicted in hieroglyphics as a boat for the god Osiris. During this time frame the Chinese were calling it the northern basket. In India over the centuries it seems that it described anything and everything that could come in a group of seven, seven sages, seven wise men, seven bulls, seven antelopes, etc.
In America it has been seen as a dipper for as far back as I can trace. It was also known as a dipper to sailors around the world. It is possible that the Big Dipper resembled the dipper that would hang by the fresh water barrel on the early boats and ships.
The Greek tale for Ursa Major, tells of Zeus and his nymph lover Callisto siring a son Arcas. When Zeus's wife, Hera, found out about Arcas, she went into a jealous rage and turned Callisto into a bear. Callisto was also cursed to wander the forest of the world for all of eternity. Meanwhile her son was raised to be a great hunter, guided by Hera. When the time was right Hera set it up so that Arcas would hunt down and slay his own mother. At the last moment, Zeus saw the plot to kill Callisto, so he reached down and grabbed her by the tail. Zeus whipped Callisto over his head and threw her far into the northern sky. It was this desperate action to save his lover that caused the unnaturally long tail. Many years later when Arcas died he joined his mother as Ursa Minor (the "Lesser Bear").
Star Hopping around the Big Dipper
Ursa Major, Coma Berenices and Virgo all contain portions of the Virgo Super Cluster of galaxies. There are about 25 galaxies in the dipper itself with many more around it. This month we will try to find some of the brighter ones in this area and a few of the fainter ones for the challenge.
I also have it broke down into two charts -- one for the dipper area and the other for the handle.
There are two stars in the dipper that we use to find Polaris. The northern most star in the Dipper is Dubhe, and 5° to the south is Merak. These stars form a line that points right to Polaris.
To start this months hop, go to Merak and put it right at the northwest edge of your finder to find NGC 3556 (M108) and NGC 3587 (M97).
M108 is an edge-on galaxy that appears as a smudge of light with a very slight brightening in the center. It has an apparent magnitude of 10.1 that is spread over a very elongated area.
M97 is a really good hit. Often called the Owl Nebula, M97 is a round planetary nebula with a visible central star that is the owl's beak. In a small scope it is hard to make out the eyes, which are two darker areas in the gas shell. If you get a chance to look at M97 in a large scope it really does look like an owl face.
Next, move your finder to the area centered between M97 and Phecda (the southern most star of the dipper). In this view you will find five galaxies, NGC 3631 to the west, NGC 3738 & 3756 to the east, and NGC 3718, 3729 very close together to the south.
NGC 3631 has two prominent arms and is magnitude 10.4. NGC 3718 is interacting with NGC 3729; NGC 3718 is the brighter of the two and has a dust lane cutting through the nucleus. NGC 3738 and NGC 3756 are a bit harder to find being close to 12th magnitude.
Continue on to the thigh of the bear Phedca, then a little farther to the southeast to find NGC 3992 (M109). M109 is rather large and brighter than all of the other galaxies so far. Look for the spiral arms and a bright nucleus. There is a star just off to the side of the nucleus but it is not part of the galaxy. For a real challenge, there is a very small galaxy just to the south of M109, at magnitude 13.9 is UGC 6923. Travel a bit farther south to find a very nice but small spiral galaxy NGC 3953.
Return to Phecda, then move to half way between Phecda and Megrez (the star that joins the handle to the dipper). At this point look for a "U" shaped cluster of five more galaxies NGC 3982, 3972, 3998, 3977 and 3990. All of these galaxies are small and 11th magnitude or fainter so you will need a good sized scope to find them.
Continue on to Megrez then travel 1½° to the North East and just past 70 UMa to find the only double star listed on Messier's list, M40. These two stars are not very special to look at but you do need them to get a Messier certificate, or complete a marathon. It appears that Messier was looking for a Supra tergum neboulosa (a "nebula above the back" of Ursa Major) that was listed as the 1496 object in Johann Hevelius' catalogue, Prodromus Astronomiac published in 1690. Messier was unable to find a nebula at the location listed in the catalogue. The only thing Messier found in the area was the two 9th magnitude stars. Feeling that Hevelius had made a mistake in his location, Messier decided to include the two stars on his list anyway.
Before moving on from M40, take a challenge and look for NGC 4290 at magnitude 12.4; this galaxy is very hard to find. Use the two stars of M40 to point you in the right direction.
There are a lot more galaxies in and around the bowl of the dipper but I am going to move on to the handle.
Follow the handle over two stars from Megrez to find Alcor and Mizar A & B, then on to Alkaid the last star in the handle. You can use the chart below or you can follow the trail of fourth magnitude stars 81, 83, 84 and 86 from Mizar to find M101.
M101 (NGC 5457) is a beautiful face-on spiral galaxy. I really like trying to see how far out I can follow the arms and looking for lighter and darker spots out towards the ends. When you get done looking at M101, move your scope just to the North for another cluster of galaxies.
This whole area of the sky is packed with galaxies. This month I hope I have helped you find a few. Try setting a full night aside and use the charts to see how many you can find. I think you will come away with a night you will remember for a long time to come.
Happy Hopping...Eric
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Lasted Updated: 11/30/2000
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