Question

omework 2 roblem 1.39 & Bot 16 Review Use two facts - Part A (1) 33 stars are within 12 light years of the Sun (2) the Milky Way disk is approximately 100,000 light- Yosnameter and 1000ght years thick Estimate the number of stars in the Milky Way, using the provided data assume that the stars are imbuted uniformly Express your answer using two significant figures. 100 AED RO? Submit * Incorrect; Try Agains attempts remaining Part B Complete previous parts) Part Complete previous parts Provide Feedback

Answer 1

The volume of the milky way is

$V=\pi(d/2)^2 h =\pi(100,000/2)^2 1000 = 2.5\times 10^{12}\pi\,ly^3$

Volume of a sphere of radius 12 ly is

$v=(4/3)\pi(12)^3 =2304\pi\,\,ly^3$

The number of stars in volume v is 33+1(Sun included) = 34

The number of stars in volume V is therefore

$N=\frac{34}{v}V=\frac{34\times 2.5\times 10^{12}}{2304}=3.69\times 10^{10}$

Up to 2 significant digits the answer is

N = 3.7 x 10¹⁰