# HW4_Cas-A - Solutions to Cas-A homework 1. This is the...

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Solutions to Cas-A homework 1. This is the conversion from radians to arcseconds. (X Radians * 206265 arcseconds / Radian.) What happens is that we approximate the very short side of a triangle to be a small arc along the circumference of a circle, whereas the other two sides are approximately equal and correspond to the radius of the circle. Since most of the distances in astronomy are vast, this is used often. In particular, it is the basis for the measurement of distances to the stars, using the radius of the Earth’s orbit as the “short” end of the triangle, and the distance to the star is the “long” end. This is how we define the “parsec”; the distance a star would be at to give a one arc second angle difference in its position in the sky, due to the Earth moving from one end of its orbit to the other, over the course of 6 months. 2. The geometry of how the knot is moving through space is not known since we can only see a 2-D projection of the remnant. Using Doppler shift though you can only

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## This note was uploaded on 10/25/2009 for the course PHYSICS Astronomy taught by Professor Me during the Spring '09 term at Akademia Ekonomiczna w Krakowie.

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HW4_Cas-A - Solutions to Cas-A homework 1. This is the...

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