On the moon's surface, lunar astronauts placed a corner reflector, off which a laser beam is periodically reflected. the distance to the moon is calculated from the round-trip time. the earth's atmosphere slows down light. assume the distance to the moon is precisely 3.84×10^8 m, and earth's atmosphere (which varies in density with altitude) is equivalent to a layer 40.0 km thick with a constant index of refraction n=1.000293. what is the difference in travel time for light that travels only through space to the moon and back and light that travels through the atmosphere and space?

Explanation:

The difference in time will be due to travel through atmosphere where speed of light slows down. If t be the thickness of atmosphere and c be the speed of light in space and μ be the refractive index of atmosphere difference in travel time will be as follows .

difference = \frac{2t\mu }{c}-\frac{2t }{c}

=\frac{2t}{c }\left ( 1-\mu  \right )

Now t = 40 x 10³m ,μ = 1.000293 , c = 3 x 10⁸.

difference =\frac{2t\mu }{c}-\frac{2t }{c}

=\frac{2t}{c }\left ( \mu -1  \right )\\

=\frac{ 2\times 40\times 10^3}{3\times10^3 }\left ( 1.000293-1 \right )\\

=7.81\times 10^{-3} s

your answer is, orbit around the nucleus