3. Alpha Centauri is the closest star system to Earth. at a distance of4.3? light years. Two astronauts. Alice and Bob. are both 19 years old. Alice travels to Alpha Centauri at 0.?c. guicklv turns around. and returns to Earth at D.?c. How old will Alice and Bob be when she gets back? 4. Consider a light source that emits light with a wavelength of 539 nm while at rest. {a} lfthe light source moves with constant velocity along a straight line path between it and the Earth. observers on Earth see a wavelength of 633 nm. What is the source's velocitv? Is it moving towards or away from the Earth? {In} If the light source were to move in the opposite direction at the same speed, what wavelength would be seen? (c) lfthe light source were to circle the Earth at the same speed. what wavelength would be seen? Note: you can ignore any gravitational redshift due to the effects of general relativity