Suppose that SETI researchers discovered a radio signal coming from a star in the direction of the centre of the Milky Way that was about 10% closer to the centre than the Sun.Humans sent a reply to this signal immediately,and the aliens replied when they got our message,how long would it take before the alien reply reached Earth?

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Quizplus · Accepted Answer

The Milky Way is about 100,000 light years across. If the signal is coming from a star closer to the center of the galaxy, then it would be farther away from us than the center. Therefore, the alien reply would have to travel at least 50,000 light years to reach Earth. Since the speed of light is finite, it would take thousands of years for the reply to reach us.

Suppose That SETI Researchers Discovered a Radio Signal Coming from a Star