Celestial hemisphere:  Northern  ·  Constellation: Andromeda (And)  ·  Contains:  Andromeda Galaxy  ·  M 110  ·  M 31  ·  M 32  ·  NGC 205  ·  NGC 221  ·  NGC 224  ·  The star 32And  ·  The star νAnd
How big is Andromeda really?, Giuseppe Donatiello
How big is Andromeda really?
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How big is Andromeda really?

How big is Andromeda really?, Giuseppe Donatiello
How big is Andromeda really?
Powered byPixInsight

How big is Andromeda really?

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Same telephoto lens for M31 and the Moon, 300mm

Let's try to graphically dispel a cliché: "Andromeda as big as 6 full moons".

Meanwhile, if by "big" we mean the major axis of the galaxy, roughly this ratio is correct, as long as we specify that we are talking about the disk (yellow dashed ellipse).

If, on the other hand, we mean "extension", the estimate is completely wrong.

Just considering the regions normally photographable from a good dark site, the galaxy occupies a region in the sky at least as large as 17 full moons. Limited to the galactic disk, there are 12, as I reported some time ago. However, if we also consider the faintest regions that can be recorded in very deep images, the extension is not less than 25 full moons, without considering the complex of tidal structures.

Enough as proof?

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How big is Andromeda really?, Giuseppe Donatiello

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