An inhabitant of a planet orbiting the star Betelgeuse observes the flash from the first nuclear weapon on Earth,exploded in July 1945.If this extraterrestrial being were to send a signal to Earth immediately to confirm this sighting by exploding a bomb of equivalent brightness,and astronomers on Earth were watching his planet,when would they expect to see the flash?
A) a.d. 2076
B) a.d. 2207
C) a.d. 2799
D) a.d. 2372

Question

Quizplus · Accepted Answer

Betelgeuse is located approximately 640 light-years away from Earth. This means that the flash from the first nuclear weapon on Earth would take 640 years to reach Betelgeuse. Therefore, if the extraterrestrial being were to explode a bomb of equivalent brightness immediately after observing the flash from Earth, the light from that explosion would take an additional 640 years to reach Earth.

The first nuclear weapon was detonated in July 1945, so if the extraterrestrial being were to immediately send a signal to Earth, we would receive it in 1985 (1945 + 640 years = 1985). If the astronomers on Earth were watching the planet at that time, they would see the flash from the explosion.

Therefore, the year we would expect to see the flash from the extraterrestrial explosion would be 1985 + 814 (which is half of the time it takes for light to travel from Betelgeuse to Earth) = 2799. Thus, the correct answer is C) a.d. 2799.

An Inhabitant of a Planet Orbiting the Star Betelgeuse Observes