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M31 - The Andromeda Galaxy
The Andromeda Galaxy is a spiral galaxy approximately 2.5 million light-years (2.4×1019 km) from Earth in the Andromeda constellation. Also known as Messier 31, M31, or NGC 224, it is often referred to as the Great Andromeda Nebula in older texts. The Andromeda Galaxy is the nearest spiral galaxy to our Milky Way galaxy, but not the nearest galaxy overall. It gets its name from the area of the sky in which it appears, the constellation of Andromeda, which was named after the mythological princess Andromeda. The Andromeda Galaxy is the largest galaxy of the Local Group, which also contains the Milky Way, the Triangulum Galaxy, and about 30 other smaller galaxies.
The Andromeda Galaxy is probably the most massive galaxy in the Local Group as well, despite earlier findings that suggested that the Milky Way contains more dark matter and could be the most massive in the grouping. The 2006 observations by the Spitzer Space Telescope revealed that M31 contains one trillion (1012) stars: at least twice the number of stars in the Milky Way galaxy, which is estimated to be 200–400 billion.
The Andromeda Galaxy is estimated to be 1.5×1012 solar masses, while the mass of the Milky Way is estimated to be 8.5×1011 solar masses. In comparison a 2009 study estimated that the Milky Way and M31 are about equal in mass, while a 2006 study put the mass of the Milky Way at ~80% of the mass of the Andromeda Galaxy. The two galaxies are expected to collide in 3.75 billion years, eventually merging to form a giant elliptical galaxy or perhaps a large disk galaxy.
At 3.4, the apparent magnitude of Andromeda Galaxy is one of the brightest of any Messier objects, making it visible to the naked eye on moonless nights even when viewed from areas with moderate light pollution. Although it appears more than six times as wide as the full Moon when photographed through a larger telescope, only the brighter central region is visible to the naked eye or when viewed using binoculars or a small telescope.
Resolving the Core
To create HDR composition of the Andromeda Galaxy I've made shorter exposures, which allowed me to reduce the regular bright halo that we often see in the images and resolve much more details around it. Faintest dust clouds can be visible very close to the brightest nucleus of the galaxy, which is actually is a double nucleus. In 1993 the Planetary Imager from the Hubble Space Telescope imaged the nucleus of the galaxy and it clearly showed a double structure. More interesting reading about it can be found HERE .
Of course 80mm refractor can't resolve it deeper, but I've been able to catch it and later process it as the smallest bright spot with swirling dust clouds around it. To create this HDR composition I've made 50 frames of 120sec each and 67 frames of 600sec. 50 frames of 2 minutes exposures wrere made to get the smoothest stack. Those frames are underexposed and very noisy and stacking not enough of them could prevent the smoothest merging of the core with longer exposures stack, so I had to make that many of them.
As for the galaxy it self I wanted to go deeper, mostly to be able to catch the Ha regions in the arms of the galaxy and of course the faintest, farthest extensions of the arms. From the dark site, doing 10 minutes exposures with F5 scope at ISO1600 gave me 45% of the histogram, which notably improved final stacking efficiency. The image didn't asked for much of noise reduction at all. While in linear stage I did touched smallest pixel scales (1-2) a bit and that's it. Whole processing done in PixInsight 1.8 and using the LRGB method.
This is actually my first light using the Zenithstar 80mm ED APO scope. This 500$ discontinued scope is far from "true APO", but it outperforms other ED doublets I have tried before. There is notable chromatic aberration with that scope, but at least it didn't produced extreme halos around bright stars and colors came out pretty much to my satisfaction. As far as I can tell, this is a more of a well corrected doublet, which controls the CA pretty well even after 10 minutes of exposures.
The WO 0.8x Reducer/Flattener III did good job but not perfect as well, there are still distorted stars along the edges. I have been advised by the William Optics support team to use the II version of their reducer which I'm going to try next time with that scope.
All in all, I got this scope second hand for 200$ in prestine condition and it's producing very satisfying results for that buck. Becides that, it's a very nice grab-n-go scope for widefield observing.
Optics : William Optics ZenithStar 80mm f/6.8 II ED APO @ f/5.4
Reducer: William Optics 2" 0.8x Apo Reducer / Field Flattener III A
Camera : Canon T3i (600D) Baader Mod
Mount : NEQ-6 Pro (Self Hypertuned/Belt Mod)
Guiding Scope: Stellarvue F50M2 Finder Scope x2 Barlow @ 400mm
Guiding Camera: SX Lodestar
Acquisition : BackyardEOS 3.0.3
Exposures : 50 x 120 sec @ ISO1600 - 1 Hours 40 Minutes
67 x 600 sec @ ISO1600 - 11 Hours 10 Minutes
Stacking : PixInsight 1.8
Processing : PixInsight 1.8