Question

If a star 100 light years away explodes
now, it will be visible to us after
(Assume speed of light to be 3 X 105
km/s)​

Answer 1

Light year is one of the basic units of measurement of distance between celestial bodies in the universe others are astronomical unit(AU) ,parsec and so on.light travels at a staggering speed of 3*10^8 metre per second,to put that into perspective in one second light can travel around the Earth 8 times .So light year is the distance travelled by light in one year .An year has 365*24*60*60 =31,536,000 seconds .This when multiplied with the speed of light gives 9,460,730,472,581 kilometres.There is nothing in the universe that travels faster than light.Even with this incredible speed light from our sun takes 8 mins to reach us ,Thus we are seeing the sun as it was 8 minutes ago.The nearest star proxima centauri is about 4 light years away so we at this very moment are seeing it as it was 4 years ago. So if a star which is 100 light years away from the earth explodes this very moment we would see the explosion exactly 1oo years from now provided we live that long which won't be true in most cases. We will be long dead before the light reaches us.our children might be fortunate to witness this event