The Andromeda Galaxy: "It's Big, And Also Faaarrr Away"

The apparent size of the Andromeda Galaxy, compared to that of the Moon. AI image created by Grok.

At 2.5 million light-years distant, or 24 million, trillion km, the Andromeda Galaxy is the furthest thing the naked eye can see. We can see it because space is mostly empty, and light from it isn't scattered much before it reaches us, unlike what happens when we view distant objects on the horizon on Earth. Mountains, for instance, sometimes appear bluish and less distinct, or even invisible. That's because moisture in the air scatters the light as it makes its way to our eyes.
The Andromeda Galaxy is incredibly distant. To paraphrase Father Ted Crilly, "It's big, and also faaarrr away." So even though it is far away, the fact that it's hundreds of thousands of light years in diameter makes it appear large in the night sky. That's when imaged with a long exposure through a telescope. In fact, it's about six times the apparent width of the Moon, but very faint. You can only see it out of the corner of your eye as a faint, fuzzy patch, and what you are seeing is the bright central bulge. The galaxy appears elliptical because, although it's actually a spiral galaxy with spiral arms, it's tilted at an angle of about 77° to the plane of the Milky Way.
 

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