Andromeda Galaxy from Deep Sky West (Jared Willson)

Andromeda Galaxy from Deep Sky West

The Andromeda Galaxy is likely the best known "island universe" outside the Milky Way itself. At a distance of roughly two and a half million light years it is the closest spiral galaxy to Earth. At a diameter of 220,000 light years, it is roughly twice the size of the Milky Way, though it may not actually be more massive. It is thought to have a mass of more than one trillion suns. Andromeda and the Milky Way are currently traveling towards each other and will collide in roughly four or five billion years and eventually merge into a giant elliptical galaxy.

Early in the twentieth century, it was thought that the Milky Way comprised the entire universe, and that so-called "spiral nebulae" were not separate galaxies, but areas of nebulosity within the Milky Way itself. Since distances could not be measured directly, there was no way to confirm this theory. Then, in 1917 astronomer Harlow Curtis noticed novae on historical photographic plates of Andromeda and also noticed that these novae were, on average, ten times fainter than novae within our own Milky Way. Debate followed within the community as to whether distant nebulae might actually be galaxies outside the Milky Way. The most famous of these debates was the Shapley-Curtis debate in 1920. The question was finally settled in 1925 by the observations of Edwin Hubble of Cepheid Variable stars in Andromeda. Cepheids Variables are extremely luminous stars that vary in brightness at a rate that has a strong correlation to their intrinsic brightness, so they can be used as "standard candles" to determine distances. Thus, Andromeda became the first "galaxy" known to be outside the Milky Way.

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Description: Fixed a bad star in the image--it was a bright star located along one of the "seams" between panels. Also, slightly tweaked the color balance to taste as the old version and a touch too much green.

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Status	Advanced success
Started	...
Astrometry.net job	5180467
PixInsight job	W3TMV4TWY6D0K1WN9HZAP30MROZKBH3M
PixInsight queue size	n/a
PixInsight stage	TASK_LOG

RA (center)	00h42m41s.54
RA (top/left)	00h50m30s.11
RA (top/right)	00h50m18s.90
RA (bottom/right)	00h34m32s.50
RA (bottom/left)	00h35m24s.70

Dec (center)	+41°16′30″.1
Dec (top/left)	+39°51′32″.6
Dec (top/right)	+42°45′30″.8
Dec (bottom/right)	+42°39′22″.10
Dec (bottom/left)	+39°45′41″.8

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