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\section{Section 1:}  The given data from the Java applet is the flux of the galaxy in $Watt/ m^2$, the velocity of the galaxy in $km/s$, and the X and Y position of the velocity data in arc seconds ("). The velocity of the galaxy was produced by the applet by taking the doppler shift of the galaxy along the line of nodes. The line of nodes is along the semi-major major  axis of the galaxy. This is important to use the line of nodes because they are along the major axis and that means that the points are taken along the maximum radial velocity. Because the radial velocity comes directly from the doppler shift, which is measured by how fast stars are moving toward or away from Earth as they revolve around the galaxy. If a star is moving away from Earth, the spectrum from the star is 'redshifted' and if the star is moving toward Earth, the spectrum is 'blueshifted.' By measuring how much the data point is blue or red shifted, astronomers can calculate a radial velocity for that point. That means that the center point of the line of nodes will have a velocity of $0 \textrm{ km/s}$ (relative to the velocity of the galaxy moving away from Earth) because the center point does not revolve around the galaxy since it is the center point. The galaxy does have a velocity at the center point because the entire galaxy is moving away from Earth and therefore the whole galaxy is redshifted by a certain amount. It is important to understand that the only reason we can measure a doppler shift is because the galaxy has an inclination toward or away from Eath. For example, an inclination of 90 degrees is edge on, and an inclination of 0 degrees is face on, and any angle in between will describe the tilt from Earth. If the galaxy is face on, we can not measure a doppler shift, and therefore a radial velocity, because the stars are not moving toward or away from Earth, they are always the same distance away.