https://www.quora.com/Is-the-speed-o...stars-the-same
Question: "Is the speed of light from all stars the same?" Answer: "Speed of light from any source, measured by any one is the same. It's a postulate in Einstein's theory of relativity and gravitation and so far it's not been proven wrong."

It HAS been proven wrong:

http://rt.com/news/225879-light-speed-slow-photons/
"Physicists manage to slow down light inside vacuum (...) ...even now the light is no longer in the mask, it's just the propagating in free space - the speed is still slow. (...) "This finding shows unambiguously that the propagation of light can be slowed below the commonly accepted figure of 299,792,458 metres per second, even when travelling in air or vacuum," co-author Romero explains in the University of Glasgow press release." x

http://www.upi.com/Science_News/2015.../1191422035480
"The speed of light is a limit, not a constant - that's what researchers in Glasgow, Scotland, say. A group of them just proved that light can be slowed down, permanently." x

https://www.youtube.com/watch?v=rM-fGNxxmSE
Glasgow researchers slow the speed of light x

http://www.pbs.org/wgbh/nova/blogs/p...y-speed-light/
"The experiment showed that it is possible for light to travel at a slower speed even in free space - and Padgett and his colleagues did it at the scale of individual photons. (...) To the researchers' surprise, the light continued to travel at the slightly slower speed even after leaving the confines of the mask." x

http://www.gmanetwork.com/news/story...ut-touching-it
"Although the maximum speed of light is a cosmological constant - made famous by Einstein's Special Theory of Relativity and E=mc^2 - it can, in fact, be slowed down: that's what optics do." x

Pentcho Valev