Saturday, October 2, 2021

Andromeda and Her Attendants

Our galaxy the Milky Way is one of several dozen galaxies that make up the Local Group of galaxies, which itself is on the outskirts of the much larger Virgo Cluster of galaxies. The largest and most dominant member of the Local Group is the famous Andromeda Galaxy (M31). M31 is thought to be bigger than our Milky Way in just about every way. It is physically larger, more massive and has more stars than the Milky Way.

If you have dark skies and know where to look on these fall evenings you can see M31 with your own eyes as a fuzzy smudge. It is worth making the effort to see it, especially knowing that this galaxy is far enough away that its light travels for 2.5 million years to reach us, making it the farthest thing that humans can usually see without a telescope (Some have claimed to see galaxy M33, which is farther, but spotting that is much more rare and difficult).

A telescope will reveal M31 as a much larger and brighter fuzzy smudge that more than fills up the field of view. It is only through photography that details such as its dark dust lanes become visible. 

The image above is a partial mosaic (that I really need to finish) of the Andromeda Galaxy that I made with my Unistellar eVscope. It reveals two of Andromeda's many companion galaxies. The round, fuzzy object to the upper left of the central portion of M31 is the dwarf elliptical galaxy known as M32 and in the lower right is M110, another dwarf elliptical galaxy that orbits M31. 

To give you a sense of depth, M32 is about 110,000 light years farther from us than M31 is, while M110 is around 400,000 light years past M31.

But M31 has more companions that can be photographed with the eVscope. One of them is NGC 147, the faint smudge at the center of the image below:

 It's not immediately obvious the NGC 147 is a companion to M31, especially since it lies some seven and a half degrees from it in our sky, but they are together in space separated by some 300,000 light years.

NGC 147's nearest neighbor in the sky is NGC 185, another satellite galaxy of M31 (below, center).

These two galaxies are both found in the constellation of Cassiopeia nearly one degree apart from each other. Of the two, NGC 185 is closer to us by some 500,000 light years, which helps to explain why it is the brightest of the two. 

Wikipedia lists more than two dozen other galaxies that are companions of M31 and I believe that all of them are out of reach from my 4.5" telescope, except possibly for one of them. Aside from M31 and the Milky Way Galaxy there is one other spiral galaxy in the Local Group, M33 in the constellation of Triangulum. It's the smallest of the three and might be in orbit around M31, we aren't certain.

At a distance of 2.73 million light years M33 is farther away than M31 and it has a much lower surface brightness too, but it has some interesting structure to it, with both star clusters and nebulae visible within it making it possibly a fine attendant of the princess Andromeda.



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