Andromeda is the closest giant galaxy to us.
At 140,000 mild years throughout, it’s 40% greater than our 100,000 mild yr diameter Milky Manner.
Andromeda is 2.5 million mild years away from us, or about 25 Milky Manner diameters. Right here’s an image to scale:
Gentle takes 2.5 million years to go between the 2 galaxies, so if a flowery Andromeda alien is viewing us with a telescope proper now, it’s seeing a bunch of Australopithecus strolling round being unappealing.
In kilometers, Andromeda is 250 quintillion km away from us. The moon is 400,000 km away, so when you had a ruler that stretched from the Earth to the moon, you’d want 625 trillion of them to achieve Andromeda.
And but, within the scheme of galactic distance, Andromeda is our subsequent door neighbor and one of many solely galaxies shut sufficient to be shifting towards us—as a result of its “brief” distance away means the pressure of gravity can overpower the motion attributable to the growth of the universe, which in virtually all different instances pulls all galaxies away from all different galaxies.
And in about 4 billion years, Andromeda will selfishly collide with the Milky Manner and the 2 will kind an extra-huge galaxy. You gained’t be right here.
Andromeda can be one of many only a few objects outdoors our Milky Manner that you would be able to see within the evening sky with our bare eye—if you already know the place to look. It seems like a fuzzy star:
However the factor is, it’s so distant that solely the super-condensed nucleus of Andromeda is brilliant sufficient to be seen to our eye, in order that’s all we’re seeing. If the entire galaxy have been brilliant sufficient, that is what you’d see at evening (with the moon as a reference)1:
Large! And on condition that it’s 2.5 million mild years away, the shocking quantity of sky house Andromeda takes up speaks to only how ridiculously giant a 140,000 mild yr diameter galaxy is.
Right here’s yet another scrumptious composite picture that reveals the relative dimension Andromeda can be within the sky, courtesy of NASA:
1 – Composite by Tom Buckley-Houston. Authentic picture of moon by Stephen Rahn.