1.0 link Rainbow Dash Network http://rainbowdash.net/ aaaaaaaaaa (aaaaaaaaa) http://rainbowdash.net/aaaaaaaaa http://rainbowdash.net/notice/146257 All that math this morning has gotten me worked up, so I imagined this fun scenario: Rainbow Dash has fallen prey to one of Pinkie Pie's diabolical pranks! Due to a paint-related mishap, her light-blue coat is now dyed green (lambda_1 = 510 nm). Not wanting to be seen in this state by you, the diligent stationary observer, she races in a straight line towards you, in an attempt to blue-shift her coat back to its original light-blue colour (lambda_2 = 480 nm). How fast must she fly in order to have you perceive her coat as its original colour? Assume Doppler shifting in flat spacetime. (For reference, the answer that I worked out is 1.8 x 10^7 m/s - much faster than the required speed for a Sonic Rainboom!).