If a star explodes 15 light years away, how long will it take for us to see it?

If a star explodes 15 light years away, how long will it take for us to see it?

• A. 1 year
• B. 3 years
• C. 15 years
• D. 30 years

Answer: (C)

Light travels at a finite speed, so distant events you see are delayed by how long light takes to reach you. A light-year is the distance light covers in one year. If the star is 15 light-years away, the light from its explosion has to travel 15 light-years to reach Earth, so we see the explosion 15 years after it happens. The other options would correspond to different distances: 1 year for 1 light-year away, 3 years for 3 light-years, and 30 years for 30 light-years.

Light travels at a finite speed, so distant events you see are delayed by how long light takes to reach you. A light-year is the distance light covers in one year. If the star is 15 light-years away, the light from its explosion has to travel 15 light-years to reach Earth, so we see the explosion 15 years after it happens. The other options would correspond to different distances: 1 year for 1 light-year away, 3 years for 3 light-years, and 30 years for 30 light-years.