The sun, which is 2.2 × 1020 m from the center of the milky way galaxy, revolves around that center once every 2.5 × 108 years. assuming each star in the galaxy has a mass equal to the sun’s mass of 2.0 × 1030 the stars are distributed uniformly in a sphere about the galactic center, and the sun is at the edge of that sphere, estimate the number of stars in the galaxy. note: the actual number of stars in the milky way is between 1011 and 4 × 1011 .

answer:

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speed of light in vacuum is 300,000 km/s

speed of light in other mediums is given by the expression v = c/n, where c is the speed of light in vacuum and n is the refractive index of medium.

for the first medium v = 200,000 km/s

  so, refractive index of medium = 300000/200000 = 1.5

    1.5 refractive index is usually for glass. so first medium is glass.

for the second medium v = 250,00 km/s

so, refractive index of medium = 300000/250000 = 1.2

    1.2 refractive index is usually for water. so second medium is water.

for the third medium v = 0 km/s

so, refractive index of medium = 300000/0 = ∞

    ∞ refractive index is usually for opaque mediums. so third medium is opaque medium.