How Big Is The Universe ?

You will never ever get you head around how big the universe is. Don't go there, its just vast it's just enormous. There is no way human mind can comprehend the true immensity of the universe. We are happy with the size of a elephant or the size of a tree or maybe even the size of a big church, but I think if we go beyond that our brain just start to run out of gas.

How The Size Of The Universe Is Measured

It may be difficult for our brain to comprehend, but that hasn't stopped endeavours to measure the distance to the stars. One technique is to use the phenomenon called parallax.

Parallax Method

Everybody can experience parallax for themselves. If you hold your thumb up and close one eye you will see that your thumb appears to be in a certain position relative to something behind your thumb, but if you open that eye and close the other eye you'll see that your thumb appears to move relative to the object behind.

The same thing happens when we look at the stars. When we look at a relative nearby star from Earth it appears in a certain position relative to the other background star. Six months later when the Earth is on the opposite side of the Sun the same star will appear in a different position relative to the background, like opening and closing one eye then the other. The star appear to move and by measuring this apparent movement we can calculate the true position of the star.

An alternative method of measurement is to use certain stars in the sky known as standard candles. We know exactly how brightly they shine. If we can therefore measure how bright they appear to us on Earth, we can calculate how far away they are. The dimmer they appear the further they are from the Earth.

So the nearest star to the Sun is Proxima Centauri and that is 40 trillion kilometres away that's 40 million million km away from the Earth.

Such number start to become incomprehensible and that's why astronomer have adopted alternative unit of measurement for such vast distances The Light Year.

What Is Light Year

 A light year is the distance that the light would travel in one year. If you imagine the light moving around the Earth in one second, the light would travel around earth over seven times just in one second. That's very fast. Speed of light is 300,000 km a second.So one light year is about 9 million million kilometres.

Are We Peeping In The Past ?

The speed of light also leads to a curious consequences when we stare at the star. Light from the Sun takes 8 minutes to get to the earth. That essentially means we are looking into the past, so we are looking at the Sun how it was 8 minutes ago.

If the sun would disappear right now we wouldn't know for 8 minutes. So a telescope is like a time machine. We're looking back in time and the further the object is away from us, the further back in time we are seeing.

Our Sun, like nearly all the star we can see with the naked eye, sits inside the galaxy we call the Milky Way, but our galaxy is not alone in the universe.  Not everything you see in the night sky is in our galaxy. It turn out that some of those faint dots are in fact the other galaxy. The farthest object you can see actually with the unaided eye is another galaxy called Andromeda, the light from that galaxy has taken something like two and a quarter million yeas to get to the Earth.

If you imagine, we can reverse the scenario and you are looking at the Earth from Andromeda with a very powerful telescope you would see no signs of cities, no civilisation, no great wall of China, but you might be seeing the age of Dinosaurs, you would be seeing how the earth was over 2 million years ago.

Astronomer has always wanted to see further using bigger and better telescopes just to find out how many other galaxies are out there, until finally we pointed the Hubble Space Telescope at what appeared to be a very dark and ordinary patch of the night sky.

If you imagine  holding up your finger with a grain of sand on it and looking at the patch of sky that grain of sand is blocks out that's the field that the telescope zoomed in on to and what the telescope saw was incredible.

Picture taken from Hubble Space Telescope on just a patch of sky we see.
Credit: NASA

Every single speck of light in this photo is a galaxy. 10,000 galaxies in a patch of sky the size of a grain of sand held at arms length. If this tiny patch of sky is like every other then we can calculate how many galaxies are out there.

The visible universe contains around 100 billion galaxies, each of those galaxies  contains about 100 billion stars. That's something like the visible universe contains 10,000 million million million stars. 

That means there are more star in the visible universe than there are grains of sand on the Earth.

The light from some of these galaxies has taken around 13 billion years to get here. That also travelling at 300,000 kilometres a second.

The visible universe stretches around 13 billion light years from the Earth.

Now just imagine how big this universe could be. Imagine the Earth as a grain of sand, if that was the case then our solar system out to the orbit of the planet Neptune would be as big as a big as Burj Khalifa. Now again shrink our solar system to the size of a sand, then our galaxy Milky way would be 1000 time bigger than the Burj Khalifa. Now again we take the size of the Milky Way galaxy and shrink it down the size of the sand grain then the Burj Khalifa would be the entire visible universe.

The Universe is big, it's really big.

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