M81 is a spiral galaxy. A spiral galaxy is essentially a disk-shaped galaxy with arms in a spiral motion (Koupelis, 2007). As a whole spiral galaxies can be divided into two subdivisions: one being an ordinary spiral galaxy and the other being a barred spiral galaxy. An ordinary spiral galaxy will have the arms coming out straight from the nucleus, or the center part of the galaxy, whereas, a barred spiral galaxy will have the arms coming out of the ends of what appear to look like bars coming out of the nucleus. Then these two subdivisions are further categorized into how tightly wound the spiral arms are. Category (a) means the arms are very tightly woven, (b) is somewhere in the middle, and (c) would be farther out, loose arms. Another thing to take note of is the color in a spiral galaxy. In this image we see blue around the arms. In the arms the material is being smashed together in a dense wave making it an ideal environment for new stars to form. The blue color shows that there are very large, hot stars forming in the arms. These are all important factors when one is analyzing and identifying a spiral galaxy.
M81 is estimated to be 12 million light years away, with an angular size of 11 arcminutes, and by using these two numbers I found the linear size of the object to be 37,600 light years. And now looking specifically at the image of M81 we can identify what kind of spiral galaxy it is. First we can easily see the disk shape of the galaxy, this is puts on the right direction in identify M81 as a spiral galaxy. Now we just have to confirm that there are arms with spiral motion. It is difficult to see the arms but in the middle of the photo near the very top border and near the very bottom border you can see some separation from the whole into what we call arms. They also appear to be moving in a spiral motion, thus we can conclude we are looking at a spiral galaxy. Next we look at the image to see if there is a bar going across the nucleus. There is not, so we conclude that we are working with an ordinary spiral galaxy. Lastly, we can observe how tightly wound the arms of this spiral galaxy are. I would consider this a category (a). Although the arms look far from the nucleus we can see that they do not expand very far from the rest of the cluster we see. As a whole the image is very compact. Through all of this analysis we can see that we are looking at a very interesting spiral galaxy. In fact, this galaxy has been viewed with the unaided naked eye by a reported four people! (Of course these observations took place on days with exceptionally good viewing conditions.)
Koupelis, Theo, and Karl F. Kuhn. In Quest of the Universe. Sudbury, MA: Jones and Bartlett, 2007. Print.
Frommert, Hartmut and Kronberg, Christine. "NGC 7293." Students for the Exploration and Development of Space. <http://www.seds.org/MESSIER/xtra/ngc/n7293.html>
|Right Ascension (J2000)||09:55:33.5|
|Filters used||B (Blue), C (Clear), R (Red), V (Green)|
|Exposure time per filter||B, V, R, and C (60s x 5)|
|Date observed||November 13, 2011|