How do us humans know that there are millions of other galaxies? If galaxies are millions of years apart, how do scientists know that there are billions of other galaxies and that andromeda is the closest?

Several very powerful telescopes, both on Earth and in space, can see objects that are billions of light years away. If we take our time to observe them and analyze the images, we can determine the average number of galaxies per volume unit and then multiply.

There are approximately 2 trillion galaxies in the observable universe, according to the most recent estimate.

How do we know Andromeda is the closest galaxy if other galaxies are millions of lightyears away?

First of all, Canis Major Dwarf, a tiny, irregular satellite galaxy located roughly 25,000 lightyears away, is the closest galaxy to the Milky Way; the Andromeda galaxy is merely the closest spiral galaxy to the Milky Way.

We use this method to determine the redshift or blueshift of every galaxy we observe to determine how far away it is. We also use common sense to determine how close something is when it is.

Humans know about the existence of millions of other galaxies through observations made using telescopes and other astronomical instruments. By studying the light emitted from distant celestial objects, scientists can determine their distance, size, and characteristics. The discovery of galaxies beyond our own Milky Way began in the early 20th century, and advancements in technology have allowed astronomers to identify and study billions of galaxies to date. Andromeda is considered the closest galaxy to the Milky Way based on its proximity and observable characteristics.