Doppler Shift Andromeda Galaxy and Collision with Milky Way

The Doppler Shift of the hydrogen alpha spectral line is calculalted for light from the Andromeda Galaxy. The Andromeda Galaxy is moving towards the Milky Way Galaxy so the shift is a "blue" shift to a slightly shorter wavelength. The distance to Andromeda and the speed of approach are used to calculate the approximate time until the two galaxies collide. Recent (2012?) observations from the Hubble Telescope show that the two galaxies will collide as the sideways motion of Andromeda is not high enough to cause the two galaxies to miss as they move towards each other. My calculation for the time to collision is less than what I commonly read in web sites. Please leave a comment if you see an error in my calculation. Introductory General Astronomy Prof. Greg Clements