@Mr BOB,
Drew Dad, Nice link. I have been there several times with mostly less than complete understanding! Since speed must always be related to two other factors, distance and time, any change in our perception of time or distance must necessarily effect what we can see.
With at least four different mechanical circumstances working on any light that we can see, Doppler, Gravitational, Obscuring, and Time Dilation it does make observations a bit chancy.
The Doppler effect is due to actual relative motion in our spacetime. Beloved by the Highway Patrol.
The time dilation effect is due to an object travelling through a space time that is probably different than ours.
The gravitational effect is due to space time falling towards mass (Earth +solar system+Milky way+local group etc. Or climbing out of a similar gravity well.
The obscurational effect is due to the loss of energy as the light encounters intergalactic hydrogen etc.
Mr Bob, The speed of light is not constant, it is "a constant". If it was constant then there would be no "Black Holes" nor Schwartzchild Radiuses. These are just the most dramatic examples but they are pretty well accepted.
So since light apparently cannot climb out of a black hole due to gravity its actual motion to an outside observer will be zero or less. However it will still be travelling at "c".
This effect is reportedly also seen in quasars in which their light is"red shifted" out of any proportion to their distance due to their mass.
Since the light is either red shifted towards infinity or actually stopped with respect to an observer then if the speed of light is constant then it seems to me that time or distance itself must change. Basically this is Hawkings position as I understand it. Time stops when and where light does. Thats why I chose "Speed of Time" as a description.
Definitely food for thought. Kind of fun! Best