What Is The M31 Andromeda Galaxy?
The M31 Andromeda Galaxy, also called the Andromeda Nebula, (catalog numbers Messier 31, M31, and NGC 224), is a barred spiral galaxy in the constellation Andromeda approximately 2.5 million light-years from Earth. It is the nearest large galaxy to the Milky Way.
M31 has a diameter of about 220,000 light-years and it shares various characteristics with the Milky Way system. With an apparent magnitude of 3.4, the Andromeda Galaxy is among the brightest of the Messier objects and the most distant object in the sky that you can see with your unaided eye from Earth on a clear night, even when viewed from areas with moderate light pollution.
The Milky Way and Andromeda galaxies are expected to collide in around 4-5 billion years. This collision will alter the structure of the two galaxies forever.
In 964, the Persian astronomer Abd al-Rahman al-Sufi described the galaxy as a “small cloud” in his “Book of Fixed Stars,” the first known report of our nearest neighbor. In 1612, the German astronomer Simon Marius gave an early description of the Andromeda Galaxy based on telescopic observations. When Charles Messier labeled it M31 in 1764, he incorrectly credited the discovery of what was then called a nebula to the German astronomer, Simon Marius, who provided the first telescopic observation of the object. The first photographs of Andromeda were taken in 1887, by Isaac Roberts.
In 2015, observations from the Hubble Space Telescope found that a halo of material surrounding Andromeda is six times larger and 1,000 times more massive than what was previously measured. (At the time, astronomers said the Milky Way may have a halo as well — and perhaps the two galaxies’ halos are already starting to merge.) This follows on from revised size estimates in 2005 and 2007, based on observing stars and star motions.
The most detailed photo of Andromeda ever was released by scientists in 2015. It was a mosaic of images from the Hubble Space Telescope.
Astrophotography
In my image above, you can see the Andromeda Galaxy with satellite galaxies M32 (center left above the galactic nucleus) and M110 (center left below the galaxy).
I took this image on several nights in September 2021 with a refractor from TS Optics, TS86SDQ Quadruplet APO Petzval design, and the ZWO ASI294MC Pro camera. Two different filters were used: the Optolong L-Pro and the STC Optical Astro Multispectra. Both filters are very good general-purpose light pollution suppression filters but I wanted to test them out to see if there are any significant differences in the final image result of each filter. In the end, I couldn’t gain much more data with the STC Optical Astro Multispectra than I wanted because of bad weather. So, at least 2/3 of the subframes in the final stack, were taken with the Optolong L-Pro. These filters can reduce the interference from artificial lighting in the city, and enhance the wavelength of Hα, Hβ, OIII, and SII. Also, do they give a nice boost to your object of interest, in this case, the Andromeda Galaxy.
I’ve used different exposures: 60 sec, 120 sec, and 300 sec. Short exposures to prevent overexposing the core. Longer exposures reveal more of the dust lanes and the outer circumference.
Although it was very humid on the first night of imaging, I managed to get good data with the Optolong L-Pro, but using a dew heater was definitely needed.
Image details
- Telescope: TS Optics TS86SDQ Quadruplet APO Petzval design
- Mount: Sky-Watcher NEQ5 Synscan GoTo
- Camera: ZWO ASI294MC Pro
- Filter: 1) Optolong L-Pro 2″ // 2) STC Optical Astro Multispectra 2″
- Telescope control: ZWO ASIair v1
- Dew Heater: DEW NOT
- Software: Astro Pixel Processor (stacking) & PixInsight (processing)
Data captured in the nights:
03/09/2021 (L-Pro); 03/09-04/09/2021 (L-Pro) & 05/09-06/09/2021 (Astro Multispectra) => Total integration time: 10.86 hours
SQM-L (average) : 19.22 -> Bortle class 6
No guiding, no coma corrector
