Understanding the Doppler Effect: Formula and Examples for Light Waves

[Stephanus]

OK. I don't mean to harass you. Please don't feel obliged to answer.

Of course NO . The answer is for me. Why in the world that I keep asking about SR, while the thing that interest me is Cosmology. It's the Twins Paradox that I tought would be easy that got me stuck in this forum for 3 month. But thank for your invaluable help all this time.