Hey guys in this article we will be discussing about the size of our universe.HOW BIG IS IT???
WHAT IS THE UNIT TO MEASURE SUCH A VAST DISTANCE???
We cannot measure long distances in kilometer or miles.....but why???
answer is very simple....it is too big value to write on a paper and hard to interpret..S we use the unit light year.
LIGHT YEAR
A light-year is a unit of distance. It is the distance that light can travel in one year. Light moves at a velocity of about 300,000 kilometers (km) each second. So in one year, it can travel about 10 trillion km. More p recisely, one light-year is equal to 9,500,000,000,000 kilometers. Light is an electromagnetic radiation having wave-particle duality making it capable to transmit itself through mediumless space-time continuums and even vacuums. But, on the other perspective, sound having properties of transverse wave cannot travel everywhere in universe.
In our solar system, we tend to describe distances in terms of the ASTRONOMICAL UNIT (AU). The AU is defined as the average distance between the Earth and the Sun. It is approximately 150 million km (93 million miles). Mercury can be said to be about 1/3 of an AU from the Sun and Pluto averages about 40 AU from the Sun. The AU, however, is not big enough of a unit when we start talking about distances to objects outside our solar system.
WE ARE ACTUALLY LOOKING AT THE PAST
When we look at the sky we see twinkling stars galaxies...The light coming from those distant stars actually started travelling years before to reach our eye.....THATS JUST AMAZING!!!!! So we are actually looking at the past. Light that leaves our second nearest star, Proxima Centauri, takes just over four years to reach Earth and so we can define it as four light years away.As such, if you were to look at Proxima Centauri, you would not be seeing the star as it is right now, but how it 'was' 4 years ago!
The universe is about 13.8 billion years old, so any light we see has to have been travelling for 13.8 billion years or less – we call this the 'observable universe'.
however the distance of the observable universe is about 46 billion light years because the universe is expanding..this means that when the light started 13.8 billion years ago at that period of time the universe has expanded so much that its distance is now 46 billion light years..
So how big is the universe???? Answer is it is so big that we dont know how big it is..LOL....It is So big that even light hasn't had time to cross it in nearly 14 billion years! And it's still getting bigger all of the time.
SOURCE: https://phys.org/news/2015-10-big-universe.html
https://starchild.gsfc.nasa.gov/docs/StarChild/questions/question19.html
https://www.quora.com/Why-the-word-light-year-is-used-to-express-distance-Why-dont-we-use-the-term-sound-year
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