[jerrygg38 (OP)]

Does a photon absorb energy when it enters a strong gravitational field differential and vice versa?
   When the photons from the sun travel toward us they travel at first from a very strong gravitational field to a weaker field as they near the Earth. At the gravitational balance point, the Earths field starts to become stronger. Finally they reach the Earth. When the Earth is moving toward the sun, we get a compressed field at the balance point. Near this point does the photons gain energy and appear blue? In the same light when the Earth is moving away from the sun the field is decompressed near the balance point. Do the photons lose energy at this point and turn red?
   It may be possible that photons constantly change every step of the way on the trip to the Earth. Alternatively photons may only gain or lose energy during strong steps in the gravitational field. Thus could photons be subject to discrete jumps in energy levels. What does present theory specify on this problem?

[evan_au]

It may be possible that photons constantly change every step of the way on the trip to the Earth.

Yes, gravitational red shift (sometimes called Einstein Shift) results in photons being red-shifted as they "climb" out of the Sun's gravitational well.

And blue-shifted as they "fall" into Earth's gravitational well.
https://en.wikipedia.org/wiki/Gravitational_redshift

This effect was originally demonstrated on Earth with photons climbing (or falling) just 22.5 meters in Earth's gravitational field, so it applies to every inch of the path from Earth to Sun (although, as you say, there is a gravitational balance point where the effect is very slight).
https://en.wikipedia.org/wiki/Pound%E2%80%93Rebka_experiment

There are two ways to look at this effect, from General Relativity:
- Photons have mass, and it takes energy to climb out of a gravitational well. This energy loss is seen as a reduction in the photon's frequency.
- Time runs more slowly deep in a gravitational well. So the frequency of the emitted photons is slower, when measured by a clock (or spectrograph) on Earth. This difference in the rate of time is seen as a reduction in the photon's frequency.

When the Earth is moving toward the sun, we get a compressed field at the balance point. Near this point does the photons gain energy and appear blue?

The Earth is on an elliptical orbit, and is it's closest point to the Sun (perihelion) in January.
Because the Earth is then deeper in the Sun's gravitational field, the photons will be less reddened by climbing out of the Sun's gravitational field. ie they lose less energy by the time they reach us. This shift is most dramatic when comparing January and July, and is most easily detectable when the Earth is not moving towards or away from the Sun.

I would not call them "bluer", because the Sun's gravitational field is far stronger than the Earth's gravitational field. Overall, the photons lose energy as they move from Sun to Earth, so they don't gain energy overall.

But a far larger effect is the Doppler effect - as the Earth is moving towards the Sun (maximum speed around September), photons are blue-shifted, and as the Earth moves away from the Sun (maximum speed around April), the photons are red-shifted. This effect is strongest when comparing September and April.

Gravitational redshift is a very subtle effect, and it takes a very strong gravitational field to detect it - it was first reported on the dwarf star Sirius B, which has a mass similar to the Sun, but a volume similar to Earth, leading to an extremely strong surface gravity.

[jerrygg38 (OP)]

It may be possible that photons constantly change every step of the way on the trip to the Earth.

Yes, gravitational red shift (sometimes called Einstein Shift) results in photons being red-shifted as they "climb" out of the Sun's gravitational well.

And blue-shifted as they "fall" into Earth's gravitational well.
https://en.wikipedia.org/wiki/Gravitational_redshift

This effect was originally demonstrated on Earth with photons climbing (or falling) just 22.5 meters in Earth's gravitational field, so it applies to every inch of the path from Earth to Sun (although, as you say, there is a gravitational balance point where the effect is very slight).
https://en.wikipedia.org/wiki/Pound%E2%80%93Rebka_experiment

  Thanks for your excellent answer. I will have to think about it and study your references. As I am studying the photon it is good when my understanding matches the present science. This helps me to physically understand what is happening within the photon.

[jerrygg38 (OP)]

I studied what was referred to and it appears in line with my thinking. The only question being that Einstein defined the results in terms of time differences and I tend to believe in actual energy flows. Thus a photon gains or loses energy. Yet Einsteins equations are excellent and either way the results must be the same. Yet my Engineering mind needs a physical model to understand things and I can picture energy differences but I cannot turn time differences into something physical although the answers are the same. I will keep thinking about it.