Galaxy Seasons

Our galaxy resembles a flat disk. Twice a year (in the summer and winter) our own galaxy fills our view of the night sky. The dense mat of stars blocks our view of anything on the other side of those portions of the Milky Way. In the fall and especially in the spring the night time sky points away from the Milky Way allowing us to see what is beyond.

What lies beyond is a lot! Fortunately the most interesting parts of what lies beyond are situated away from the plane of our galaxy. Their representation on flat paper (or your computer screen) limits the two pictures below. Keep in mind that there is a 3rd dimension that is poorly represented.

Fall Galaxy Season

In the fall the Milky Way passes through from the summer constellation Cygnus through Cassiopeia then Perseus and onto the Winter Milky Way. Located just off the plane in this direction are the largest members of our Local Group. The Local Group is collection of Galaxies within about 10 million light years of earth. The most easily seen members are the Andromeda Group (M 31, 32, and 110) and M33. More challenging members are NGC 147 and 185. NGC 6822 is closer than Andromeda, but is located just off the plane of the Milky Way in Sagittarius.

Since the Local Group galaxies are “close” they are moving together instead of flying apart. As you probably heard, the Milky Way and similar sized Andromeda Galaxies will collide at some point in the distant future.

At the same time below the equator (what would be spring for them), it is possible to view the two nearest mini galaxies the Magellanic Clouds. These are the largest of a number of dwarf galaxies orbiting the Milky Way.

We also have an opportunity to see much more distant galaxies. The Perseus-Pisces Super cluster is at a distance of 250 Mly. Abell 262 (NGC 708) is one of the groups of this supercluster.

Spring Galaxy Season

Galaxy groups are like a set of Russian Dolls, each fits inside the next. Similarly, the Local Group is a part of the bigger Virgo Super Cluster. Spring is the time to see the components that make up the Super Cluster. The distances to these galaxies are vast compared to the Local Group. (See a picture of the local group here .) M81/82 is the closest member at a mere 11 mly. The Group of Galaxies in Virgo comprises the largest part of the group. They are about 65 Mly away.

The members and distances to the supercluster members are shown in the NASA drawing below. The Spring Galaxies comprise a band that runs from Leo north to Ursa Major and Draco. The densest portion is between RA 11 and 13 above Declination -20.

The north Galactic Pole (90 degrees from the plane of the galaxy) is located in Coma Berenices. Because the Milky Way is out of the way we get to see our distant neighbors. Unlike the galaxies of the local group these are moving away from us as the universe expands.

See Mark Wagner’s article (pg. 2) in this edition for observing suggestions.

Get out and enjoy the season.

Many astronomers (myself included) look forward to the challenge and reward of the galaxy seasons. To observe them the best you have to get away from the city. The TAC list (www.observers.org) will give you suggestions of sites that are open to astronomers and with what restrictions. They will also give you an idea of where other amateurs are observing.

Many galaxies are just faint blobs, but others have interesting structure or proximity to other galaxies. I particularly call your attention to the eye candy list (http://observers.org/observing/eyecandy/index.html) for a list of objects that are the next step beyond the Messier List.

Bring as much aperture as you can. However, do not think you need to pack the Keck to see anything. I had a ball in the dark skies of Arizona with just a 100mm Orion Short Tube. You will need charts and hopping techniques as taught in our star hopping classes (www.sjaa.net/bw). Unfortunately, you can not use filters to make galaxies more visible since they tend to emit strongest in the light the filters filter. There is no substitute for dark skies.

Being out also give you a chance to enjoy the more reliable and warmer spring weather.

Material from Wikipedia was used in the preparation of this article.