The Great What in Andromeda???!!!
It is hard to believe that it has only been a little over 100 years since humanity has known that the "Spiral Nebulae" we were observing were other galaxies outside of our home galaxy, the Milky Way. The key piece of evidence of this came when Edwin Hubble recognized that a star in Andromeda was a special kind of variable star, allowing him to estimate the enormous distance to it. It is one of the first objects other than the Moon or Planets that I observed through a telescope/binoculars.
Here's an image of The Andromeda Galaxy(M31) captured from backyard on 9/19/2025 with my wide-field imaging rig:
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| M31 - The Andromeda Galaxy captured from my backyard on 9/19/2025. |
What is it? (Written with AI assistance):
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| An Annotated version of the image. |
M31
Andromeda Galaxy (M31, NGC 224) — A large, nearby spiral galaxy with a bright central bulge and extended spiral disk visible in deep images. Role: M31 is the nearest major galaxy to the Milky Way and the dominant member of the Local Group. Key properties: contains roughly a trillion stars, lies about 2.5 million light‑years away, and spans on the order of 150–200 thousand light‑years across. The image shows the luminous core, surrounding spiral structure, and dust lanes that trace the galaxy’s arms.
M32
Messier 32 — A compact dwarf elliptical satellite immediately adjacent to M31’s core. Appearance: small, high surface‑brightness object that appears round and concentrated. Significance: likely a tidally stripped remnant that has lost outer stars to M31, making it a useful tracer of interactions and the gravitational environment near Andromeda’s center.
M110
Messier 110 — A more diffuse dwarf elliptical satellite located near M31. Appearance: larger and fainter than M32 with an oval, low surface‑brightness profile. Notes: M110 shows evidence of mixed stellar populations and tidal disturbance from past encounters with M31.
NGC 206
NGC 206 — A bright star cloud or giant OB association located in one of M31’s spiral arms. Appearance: appears as a compact, luminous knot within the disk. Significance: one of the largest young star complexes in the Local Group, rich in massive, blue stars and open clusters.
Foreground Stars
53 v And and 32 And — Bright stars in the constellation Andromeda that lie in the foreground of the M31 field.
Hubble’s Observations and the Recognition of Other Galaxies
Edwin Hubble identified Cepheid variable stars in M31 and used their pulsation periods to measure the galaxy’s distance. His measurements showed that M31 is far outside the Milky Way, proving that the “spiral nebulae” are separate galaxies. This discovery ended the debate about the scale of the universe, opened the field of extragalactic astronomy, and set the stage for later work on galaxy distances and cosmic expansion.
How big is it?
M31 has an angular distance of 189.1 x 61.7 arcminutes (1 degree is 60 arcminutes) on the night sky. For reference, the Sun and the Moon have an angular distance of 31 arcminutes on the sky. Andromeda is about 150,000 to 200,000 light-years (ly) in diameter.
How far is it?
M31 is located about 2.5 million light-years (ly) from Earth in the Constellation Andromeda.
How to find it?
M31 is relatively easy to find. From a dark site, with no bright Moon, it can be seen as fuzzy star with no optical aid. This s one of the most distant objects that can be seen with the unaided eye. This object can observed with Binoculars or a Telescope. A wide field of view is useful as M31 takes just over 3 degrees on the night sky (6 times the angular size of the Moon).
- Find the Great Square of Pegasus
- Find the corner star Alpheratz (technically it belongs to Andromeda not Pegasus).
- Follow the bottom line of stars in andromeda until you get to Mirach.
- Hop to uAnd (Mu Andromedae) on the top line in Andromeda.
- Hop to vAnd (Nu Andromedae).
- M 31 is just off of vAnd.
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| Finder Chart for M31. |
Imaging Notes:
Friday September 19th was forecast to be clear all night. After getting home from work, I set up my wide-field imaging rig. Since the moon was heading towards New Moon (3% Waning Crescent), no filter was used and a broadband target was selected. Actually, I collected some more data on a project that I've been working since August. M31 was my second target, after the first target was lost to the trees.
The first sub rolled in at 12:22 AM. The skies were ok. Transparency and seeing were average. I went to sleep around 1:30 AM. The rig kept collecting subs until 4:36 AM. A total of 111 good sub exposures were collected.
Processing:
All pre and post processing was performed in PixInsight. Pre-Processing: All subs were visually inspected with Blink and subs with issues were removed. All light Frames, Flats, Darks and Dark flats were loaded into WBPP. Linear Post Processing: Background extraction was performed with GraXpert followed by BXT (correct only). SPCC was used for Color Calibration followed by a full application of BXT. The Stars were removed using StarXT. Starless Linear: Noise was reduced with NXT. The image was made non-linear with HT. Linear Stars: The stars were made non-linear with Seti Astro's Star Stretch Script.
Non-linear Post Processing: Starless: The Create HDRImage script was used to recover detail in the core of the galaxy. Color, intensity, and contrast were adjusted with various applications of CT. Saturation was increased with CT. Sharpening was performed with the Image Blend Script. LHE was applied at 2 kernel sizes and Unsharp mask was applied. The DSE script was used to enhance dust lanes in the galaxies core. Stars: Saturation was increased with CT. Final: The Stars and Starless images were combined with Pixel Math to produce the final image.
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