The distance between the stars is so large that Kilometers becomes a very small unit.

Hence, the distance between stars and planets are expressed in light years.

One Light Year means Distance travelled by light in 1 Year.

 

Calculating 1 Light Year

Speed of Light = 3 × 10 8 m/s

     Time = 1 Year

   = 365 days

   = 365 × 24 hours

   = 31536000 seconds

 

Now,

1 Light Year = Speed × Time

= 3 × 10 8 × 31536000 m

= 94608000 × 10 8 m

= 94608000 × 10 8 × 1/000 km

= 94608 × 10 8 km

= 9.4608 × 10 4 × 10 8 km

= 9.4608 × 10 12 km

 

How much time will it take for light to reach from sun to earth?

 

Distance of sun to earth = 150000000 km

    Speed of Light = 300000 km/second

 

Time taken = 150000000/300000 seconds

        = 500 seconds

Time taken in minutes = 500 second/60

                          = 8.33 minutes

So, it takes around 8 minutes for Sunlight to reach earth

The next closest star is Proxima Centauri, 4.3 light years away.

So, if we see a light from that star today. It means the light we are seeing was actually 4.3 years ago

Light Year Scale.jpg

Note: Light year is a unit of distance. Not time.

 

  1. Class 8
  2. Chapter 17 Class 8 - Stars and the Solar System

About the Author

Davneet Singh's photo - Teacher, Computer Engineer, Marketer
Davneet Singh
Davneet Singh is a graduate from Indian Institute of Technology, Kanpur. He has been teaching from the past 9 years. He provides courses for Maths and Science at Teachoo.