Question

suppose a star which is 100 light years from earth if it explodes today after how much time this explosion will visible to people on earth

Answer 1

100 years more would be required for people on earth to see the explosion as lighr itself will take 100 uears to travel from the star to earth.

Answer 2

100 lights years because if it is 100 years away from us then we see its 100 light years past .. after it explodes we will able to see its explosion after 100 light years... but we should be alive to see that