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Part I. Lookback Time to Andromeda 1. Use the distance to the Andromeda Galaxy (2.4x10km) and the speed of light to determine the look back time to the galaxy 2.506 years SAVE & CHECK VIEW CORRECT ANSWER Correct Show your work distance velocity x time 2.4 x 10^19km/3.0 x 10^5 km/s = 8.0x10^13 sec = 2.5x10^6 SAVE Saved 2. Put this into context by thinking about and looking up) what was happening on Earth when the light we see from M31 was emitted. There was spotted various novae in Andromeda, and was accused of it being a separate galaxy. Also, was described as a 'small cloud SAVE Saved PLAY ACTIVITY

TULI LUU UISCULOn Assignment Wrapping It Up 2. Now calculate the velocity of each side using the Doppler shift formula for light, the rest wavelength, and the observed wavelengths for each side. a. Rest wavelength: 4860.09 Angstroms SAVE & CHECK VIEW CORRECT ANSWER Correct b. Observed wavelength left: 4858.69 Angstroms SAVE & CHECK VIEW CORRECT ANSWER Correct c. Observed wavelength right: 4853.38 Angstroms SAVE & CHECK VIEW CORRECT ANSWER Correct d. Velocity left: -62 km/s SAVE & CHECK VIEW CORRECT ANSWER Correct Show your work: SAVE e. Velocity right: -414 km/s SAVE & CHECK VIEW CORRECT ANSWER Correct

SAVE e. Velocity right: 414 km/s SAVE & CHECK VIEW CORRECT ANSWER Correct Show your work: SAVE 3. Average the velocities from opposite sides to obtain the systemic velocity (overall speed through space) of the Andromeda Galaxy -250 km/s SAVE & CHECKT VIEW CORRECT ANSWER Correct Is it moving toward or away from us? SAVE Show your work:

-250 km/s SAVE & CHECK V IEW CORRECT ANSWER Is it moving toward or away from us? SAVE Show your work SAVE 4. Now take the difference between the velocities you measured for the left and right hand sides of the galaxy, and divide by two to find the average rotational velocity of the Andromeda galaxy 1-154 km/s SAVE & CHECK VIEW CORRECT ANSWER Correct Show your work SAVE

SAVE Part III: Time to collide with the Milky Way 1. Use the distance to the galaxy from part I and the systemic velocity from part il to calculate how long it will take for M31 to collide with the Milky Way. 4 billion years SAVE & CHECK VIEW CORRECT ANSWER Correct Show your work SAVE Saved -PREVIOUS MacBook Air