送交者: DBS 于 August 18, 2001 04:47:46:
回答: 剩下的，周末愉快 由 红胡子 于 August 17, 2001 21:05:40:
Dear HL,
My most important discovery tonight is that I would fail a college entrance exam if I were going to take
it now:-).
After some warmming up, it seems to me that the percentage red-shift (Doppler effect) should be related only
to the relative speed between the light emitting object (star) and the observation point. Therefore the distance
in between (i.e. that "6 billion year" of light travel) is irrelavant. So your question boils downs to how fast
the light emitting star is moving relative to us. Let's take Edwin Hubble's work in 1920's for example (see
the PBS link below), in that case a star he saw moves at a speed of v = 1 X 10^6 m/s, therefore the red-shit
would be about 0.3335641% (i.e. lambda'=(1+v/c)lambda --I rederived it, didn't check but should be about right,
use c = 2.99792458 x 10^8 m/s). Therefore for hydrogen emissions, e.g. the spectroscopic lines lambda1 = 410.17
nm and lambda2 = 434.05 nm the observed results on earth should be lambda1' = 411.54 nm and lambda2' = 435.50 nm,
as Hubble observed.
We should have XPY's stamp on it before letting others quote these:-).
DBS
P.S. There is a typo on the PBS link page: the wording "0.0033 percent" should have been "0.33 percent".