- Location: Photographers backyard, Rostov Oblast, Russia
- Date taken: Aug. 27, 2016, Aug. 28, 2016, Sept. 1, 2016, Sept. 2, 2016
- Camera: Canon EOS 600D
- Optics: Synta BK P150750
- Mount: Sky-Watcher NEQ6 PRO SynScan
- Guiding telescope: TS Optics 50 mm DeLuxe
- Guiding camera: ZWO ASI174MM
- Focal reducer: Baader Planetarium MPCC Mark III
- Accessories: Astroimpex Bahtinov focusing mask, Sky-Watcher Electric Focuser
- Exposure time: 210 x 300 seconds @ ISO 200 (total 17.5 hours)
- Avg. Moon age: 19.75 days
- Avg. Moon phase: 12.63%
- Bortle Dark-Sky Scale: 5.00
- Temperature: 17.67 degrees celsius
- Pixel scale: 1.170 arcsec/pixel
- Orientation: -75.654 degrees
- Field radius: 1.004 degrees
The Andromeda Galaxy, also known as Messier 31, M31, or NGC 224, is a spiral galaxy approximately 780 kiloparsecs (2.5 million light-years) from Earth. It is the nearest major galaxy to the Milky Way and was often referred to as the Great Andromeda Nebula in older texts. It received its name from the area of the sky in which it appears, the constellation of Andromeda, which was named after the mythological princess Andromeda.
Being approximately 220,000 light years across, Andromeda is the largest galaxy of the Local Group, which also contains the Milky Way, the Triangulum Galaxy, and about 44 other smaller galaxies. Despite earlier findings that suggested that the Milky Way contains more dark matter and could be the largest in the grouping, in 2006 observations revealed that Andromeda contains one trillion (1012) stars: at least twice the number of stars in the Milky Way, which is estimated to be 200–400 billion.
The mass of the Andromeda Galaxy is estimated to be 1.5×1012 solar masses, while 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 approximated the mass of the Milky Way at 80% of the mass of the Andromeda Galaxy.
The apparent magnitude of the Andromeda Galaxy, at 3.4, is among the brightest of the Messier objects, making it visible to the naked eye on moonless nights, even when viewed from areas with moderate light pollution.
The Milky Way and Andromeda are expected to collide in 3.75 billion years, eventually merging to form a giant elliptical galaxy or perhaps a large disc galaxy.
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