Space , probably one of the most fascinating topic to discuss within the human race , is the region which has startled the humanity from the time immemorial . Despite of all the scientific achievements until 21st Century , there is a lot more hidden in the area beyond our imagination , what we call it as the Universe.


From the ancient times, we humans have observed the celestial objects in the space , some surprisingly clear while others faintly. All of us know that Galaxy is a collection of stars , clouds , dust and planets , and our's is called The Milky Way Galaxy. Unfortunately , For a long time this Galaxy was thought of entire Universe.

Luckily , in 1924 American Astronomer , Edwin Hubble can up with a thesis that our galaxy was not alone in this entire Universe , but there exists many of them at some distance. To proove his theory , Edwin Hubble needed to find out the distance between two such galaxies.

The Apparent brightness of a star depends on two factors - Luminosity and it's distance from the observer.

The above line states that if we know the Luminosity and the Distance of any star , we can come up with it's Apparent Brightness . Similarly we can also predict the distance of the star , if we know its Luminosity and Apparent Brightness. According to Edwin Hubble, there exists some stars whose Luminosity is always same (i.e. Constant) when measured while they were near us. If such stars get detected in another galaxy (So their Luminosity is same) , we can coversely calculate the star's distance from us.
If we could calculate this distance for more than one star, and the value each time come approximatley same , we can devise the distance between such galaxies.

Hubble later on found out the distance of 9 different galaxies from ours.

Now , With the help of modern sophisticated telescopes we have observed around a hundred thousand million galaxies including ours' and more astonishingly each galaxy comprise of some hundred thousand million stars (Now Imagine the vastness of this Universe !)