Andromeda is the largest galaxy closest to us.

With a diameter of 140,000 light years, it is 40% larger than our Milky Way galaxy, which has a diameter of 100,000 light years.

Located 2.5 million light years away, Andromeda is approximately 25 times the diameter of the Milky Way galaxy. The scale of this distance can be visualized in the image below:

It takes light 2.5 million years to travel between these two galaxies. If an advanced alien civilization in Andromeda were observing Earth through a telescope now, they would see primitive Australopithecus wandering the planet.

In terms of kilometers, Andromeda is 250 quintillion km away from us. To illustrate this vast distance, if you lined up rulers from Earth to the moon, you would need 625 trillion rulers to reach Andromeda.

Despite this immense distance, Andromeda is considered a close neighbor in astronomical terms. It is one of the few galaxies moving towards us due to its relative proximity. This is because the gravitational force between Andromeda and the Milky Way overcomes the universe’s expansion, which usually causes galaxies to drift apart.

In approximately 4 billion years, Andromeda and the Milky Way will collide, ultimately merging into a single, larger galaxy, an event that will occur long after our time.

Andromeda is one of the rare celestial objects beyond our Milky Way that can be seen with the naked eye as a faint, fuzzy star in the night sky, provided you know where to look:

However, due to its distance, only the densely packed core of Andromeda is bright enough to be visible. If the entire galaxy emitted enough light, you would witness a spectacular display in the night sky, as depicted in the image below:

Remarkably, even at a distance of 2.5 million light years, Andromeda fills a significant portion of the sky, underscoring the vastness of a galaxy with a 140,000 light year diameter.

Another composite image from NASA provides a visual representation of the size Andromeda would occupy in the night sky:

1 – Composite image by Tom Buckley-Houston. Original moon photo by Stephen Rahn.