Week 4, clip 8

Timepoint:  04:06.8

1) Consider a star that is 3 parsecs away and moves transversely across the sky 0.05 arcseconds per year.  How many kilometers per second is its transverse velocity?  Round your answer to two significant digits.

Timepoint:  05:24.5

2) Consider another star, a distance of 4 parsecs away with a transverse motion of 0.2 arcseconds per year.  This same star also has an observed wavelength for a hydrogen line of 434.102 nanometers, which is measured in a lab on Earth to be 434.1 nanometers.  What is the true total velocity of this star, in kilometers per second? Round your answer to two significant digits.

Answers:
1) [0.7,0.8] is the accepted range.

2) [3.6,4.4] is the accepted range.

Explanation:
First, use v_T = 4.74  \mu  D

Second, use v_r = c  ( \frac{\lambda}{\lambda_0} - 1)

Lastly, use the Pythagorean formula to find the vector sum of the two velocities, v^2 = v_T^2 + v_r^2