We look at the night sky and everything seems equally distant from our point of view. The reality is quite different. Astronomers study celestial objects and can determine their distance from Earth. To the right an image taken from VAO(Vazquez Astronomical Observatory). The first one to the right is of a distant galaxy named Mark876. But where is the galaxy in that image? Well is very small and point like. Just like any other star in that image. That is because this galaxy is so far away from us that it looks as just another star in the sky. What we see, is its bright nucleus at a distance of 476.5 Mpc. A parsec is 30,857 billion kilometers.
The second image reveals M101 also known as the Pinwheel galaxy. It is a spiral galaxy and there is no mistake, we can tell by the look of it that it is indeed a galaxy. How far is it? It is merely 3.4 Mpc away. That is just 104,739,957,746,478,873,239 km away from Earth. Definitely closer than Mrk 876. How do we know the galaxy is so far away? Lucky for us there are stars in the universe called Cepheids, which change brightness periodically. Using their change of brightness we can determine their distance to Earth. Galaxies like M101 are beautiful sights for astrophotographers.
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