This week's questions come from the reading about the doppler effect [Universe 5(9)] and the expanding universe
        [Universe section 26(5)]

    1.  This question is about sound.  How fast would you have to be moving relative to a singer  who is belting out a concert A note (frequency = 440 Hz) in order for you to hear that note as an A# (A sharp, frequency =  466 Hz, the next semitone higher up on the scale)? 

         Is this a speed that reasonable human beings frequently experience?

         To hear an A#, how would you have to be moving (direction-wise) relative to the singer?

 
   2. Suppose we now switch waves and consider the doppler effect in light.  How fast 
would you have to move relative to a light source for it to change to the adjacent color?

For example, if you wanted the green in a traffic light to appear blue, what speed is required?

How (direction-wise) does the observer have to be moving in order for green to appear blue?

Once again, a speed that humans experience?

   3.  a) What observational evidence is there to support the claim that the universe is expanding?

    b) Hubble's law says that the recessional speed of a galaxy (relative to us) is proportional to its distance from us.
        why is that?  what causes that proportionality to be true?  [or, what are the implications of that proportionality?
        what does it tell us about the universe?]