Homework Help: Gravitational red shift question

1. Aug 16, 2005

asdf1

Why does the frequency of a photon emitted from the surface of a star decrease as it moves away from the star?
if hf=hf(1-GM/(R*c^2)
then as the distance becomes larger, R becomes larger, so fbecomes smaller?

2. Aug 16, 2005

TD

We use the fact that the total energy must remain constant.
I'm not 100% sure, but I think t hat when leaving the star, the photon has to get out of the gravitation-field of the star, therefore its kinetic energy has to decrease since the potential energy is rising.

3. Aug 17, 2005

asdf1

hmm... that makes sense, but the mathematical equation looks weird...
it seems to say otherwise~

4. Aug 18, 2005

asdf1

still a little weird~