Our Closest Galactic Neighbors

Science Fridays 

Post # 89 

      I live out in the country, in the big woods.  Although I have three neighbors right across the road from me, we are like an island, or rather a small archipelago.  There isn't anyone else near me for at least a half mile one way, and a full mile the other direction.  We're spread out like that here.  Drive about a mile, and then there's a small cluster of houses, go another half mile and then there's the lone cattle or horse farm.  Therefore we consider someone who lives up to five miles away as one of our neighbors. 
      In Minnesota, on a larher scale, the towns and cities are like that too.  You go down the freeway for about fifteen miles or so, and then there's a small cluster of small communities.  There's one larger one, and then smaller ones that are almost like satellite towns.  And then there's the Twin Cities, Rochester, Saint Cloud, and Albert Lea - each of them has smaller communities that turned into suburbs (The Iron Range towns are like a bunch of small suburbs that have no main hub city).  
      On a very much larger scale, a galactic scale, it is the same way.  Most galaxies have satellite galaxies orbiting around them.  Our own Milky Way has several.  The most prominent of these are the Large and Small Magellanic Clouds, the Pegasus Galaxy, and Leo I, II, and III.  They are technically separate galaxies, and are therefore our closest galactic neighbors (in Stargate Atlantis they were in the Pegasus Galaxy, and were too far away to get to by gates.  They had to travel there by Asgard ships until the creation of a series of gates known as the Carter/MacKay Bridge).  Looking at things from an urban/suburban viewpoint you could say that they are all just really a part of the Milky Way.  They do orbit us, after all. 

                                                       The Large Magellanic Cloud

      Looking at it that way, we would have to say that the Andromeda Galaxy is our closest galactic neighbor, along with its satellites (suburbs).  But just how close is Andromeda. 
      If I told you how many light years away (a lot), you would have no real concept of how close it is.  It is a concept that is hard to wrap our heads around. 
      The Milky Way is about 100,000 light years across, and almost twice that distance if you count all our satellite/suburb galaxies.  Andromeda, our giant neighbor is twice that at about 200,000 light years, and counting its orbiting, suburb galaxies it is about twice that at 400,000 light years across.  Presently Andromeda is is about 2,000,000 light years away from galactic center to galactic center.  From edge to edge however, Andromeda is only about 1,700,000 light years away (you're probably thinking, "only?  This Wisenheimer is calling 1,700,000 light years 'only'?")  Looking at it another way Andromeda is only five times its diameter away from us.  That's really close - and it's getting closer. 
      Yes, Andromeda is speeding toward us.  Presently it takes up a huge portion of our night sky.  It takes up about 6 1/2 "moon widths."  Through the naked eye however, it only appears as a fuzzy looking area (on a clear night away from any cities, such as at my place).  NASA's Astronomy Picture of the Day web site recently created a composite picture to show Andromeda's size in our night sky (picture below). 

      Astronomers say that in about 1000 to 10;000 years it will be so close that it will take up our entire northern sky.  It will continue to look larger and larger until it collides with our own galaxy.  It will swallow up our own galactic center and take many of our stars with it, leaving the remnant along with our own suburb galaxies to orbit as a new satellite-suburb galaxy.  Talk about consolidation!  That won't happen though, they say until about 3 million years from now.  Various college astronomy departments have published videos of this whole scenario.  

      I'm going to be gone again at another reenactment this weekend, so there will be no more posts again until at least Monday night.  Have a great weekend.  I will.