In special relativity,
in the observerís frame the speed of light is fixed
at c. The SR postulate
is that the speed of light
is the same to every observer (i.e., in every observerís frame). So
any light from any observed source anywhere in the universe in his
frame Ė regardless of its motion -- will be seen IN THE OBSERVERíS
FRAME as moving
at c with respect to him.
Of course, as the object varies
its speed, the color (frequency) of its light observed by the observer
can be seen to shift up or down a bit in the spectrum, depending on
the relative direction.
In "Fer de Lance" I
learned why an object moving with respect to an observer appears to
gain mass [Page 39] in accordance with OGR.
Can you also explain why any motion toward or away from a light source
has no effect on c as
measured by the observer, in accordance with OSR?