How To Measure Distances In The Universe

The distances between heavenly bodies in space are very, very large. Measuring these distances in kilometers would mean dealing with very large numbers. The Sun, which is the star nearest to us, is 15,00,00,000 km away. The next star nearest to us is Proxima Centauri, which is 4,00,00,00,00,oo,ooo km away. This, you will realize, is very inconvenient to write or to make calculations with.

    Astronomers, therefore, use special units to measure distances in space. Instead of a kilometer, they use a unit called light year. A light year is the distance that light travels in one year.

       Light travels at an incredible speed of about 3,00,000 km/s. If a spaceship could travel at this speed, it would reach the Moon in just over 1 second!

    So, 1 light year = Speed of light in km/s * number of seconds in a year

     = 3,00,000 * 365* 24* 60* 60 km

     = 95,00,00,00,00,00 km (approximately)

                   12

     = 9.5 * 10

In this respect, Proxima Centauri is 4.3 light years away from us. Light from this star takes over four whole years to reach us. This also means that when you look at Proxima Centauri today, you see it as it was 4.3 years ago!

      

   Time taken for light to reach Earth from Sun

= distance of arth from sun

       Speed of light

=15,00,00,000 km  = 500 s = 8.3 min            

   3,00,000 km/s         

So we can say distance of Earth from Sun is 8.3 light minutes.