The Andromeda Galaxy , also known as Messier 31, M31, or NGC 224 and originally the Andromeda Nebula, is a barred spiral galaxy approximately 2.5 million light-years (770 kiloparsecs) from Earth and the nearest large galaxy to the Milky Way. 

The galaxy's name stems from the area of Earth's sky in which it appears, the constellation of Andromeda, which itself is named after the Ethiopian (or Phoenician) princess who was the wife of Perseus in Greek mythology. 

The virial mass of the Andromeda Galaxy is of the same order of magnitude as that of the Milky Way, at 1 trillion solar masses (2.0×1042 kilograms). The mass of either galaxy is difficult to estimate with any accuracy, but it was long thought that the Andromeda Galaxy is more massive than the Milky Way by a margin of some 25% to 50%. This has been called into question by a 2018 study that cited a lower estimate on the mass of the Andromeda Galaxy, combined with preliminary reports on a 2019 study estimating a higher mass of the Milky Way. The Andromeda Galaxy has a diameter of about 220,000 ly (67 kpc), making it the largest member of the Local Group in terms of extension.  The number of stars contained in the Andromeda Galaxy is estimated at one trillion (1×1012), or roughly twice the number estimated for the Milky Way. 

The Milky Way and Andromeda galaxies are expected to collide in around 4-5 billion years, merging to form a giant elliptical galaxy or a large lenticular galaxy. With an apparent magnitude of 3.4, the Andromeda Galaxy is among the brightest of the Messier objects, making it visible to the naked eye from Earth on moonless nights, even when viewed from areas with moderate light pollution. 

Under most viewing conditions, the Andromeda Galaxy is one of the most distant objects that can be seen with the naked eye (M33 can be seen under very dark skies). The galaxy is commonly located in the sky in reference to the constellations Cassiopeia and Pegasus. Andromeda is best seen during autumn nights in the Northern Hemisphere when it passes high overhead, reaching its highest point around midnight in October, and two hours earlier each successive month.

In early evening, it rises in the east in September and sets in the west in February. From the Southern Hemisphere the Andromeda Galaxy is visible between October and December, best viewed from as far north as possible. Binoculars can reveal some larger structures of the galaxy and its two brightest satellite galaxies, M32 and M110. An amateur telescope can reveal Andromeda's disk, some of its brightest globular clusters, dark dust lanes and the large star cloud NGC 206.  [Source:  Wikipedia]

An extensive description in Wikipedia can be found here:      https://en.wikipedia.org/wiki/Andromeda_Galaxy

The image was captured with the iOptron CEM120 mount , the TMB80SS F6.3 Refractor coupled with an Orion Field Flattener , and my old Canon 450D XSi camera.

This is a two panel mosaic with the upper half of the image being Panel no.1 and the lower half Panel no.2.

All subs were taken a ISO1600 and 120s each.  All were done at ambient temperature that varied between 21C and 34C.

IMAGE information -- 2021
Subs (ISO1600, 120s):
Panel no.1:  89 subs (2.97hr) on Oct 9th, 14th and 15th.
Panel no.2:  90 subs (3.00hr) on Oct 11th, 14th and 15th.

Processing was done with PixInsight, following reasonably good practices I’ve developed over the years.

COMMENTS:
This was a two panel mosaic processed in PixInsight.  This is a pretty good image considering the use of my old trusty Canon 450D XSi with only  5.97 hours of integration time.   I had imaged M31 back in August of 2010 using the same scope and camera, but  different capture and processing software.  Don't remember why I didn't post it on the Astrobin site.  I'd like to think though that this one is better.

My trusty Atik 383L+mono CCD camera is still lost.  Although as of the last contact with USPS, they say the camera is still in Portuguese customs and yet to be delivered to the service center.  Again, we shall see.

The  new QHY294M Pro cmos camera from High Point Scientific is still on order with no definite delivery date.