Question

If we see a supernova of a star that is 25 light years away from us, we know it exploded 25 years ago.

True
False

Answer 1

True! A lightyear is the distance that light travels in a year. The light from the supernova would take 25 years to travel 25 lightyears to Earth for us to see.

Answer 2

True

Step-by-step explanation:

- Primarily, a light year is a unit of distance. So 1 light year is equivalent to 9.46 x 10^12 km that a light travels in one Julian year i.e 365.25 day.

- Hence, so for an object 25 light years away the time it takes to reach us:

t = (25*9.46*10^15 m) / (3*10^8 m/s)

t = 25 years.

- Hence, it takes 25 years for the light to travel through vacuum to travel 25 light years.