Posted: Mar 24, 2017 7:16 pm
by newolder
jamest wrote:
newolder wrote:
I'm easily confused. Could you ask the question again, please?

If it's the one about measuring distances to galaxies then that concerns finding 'standard candles' that shine equally in all galaxies.

This leads me to ask another question (sorry squire!) : apparently red-shifted light has less energy, so why would these standard candles not vary in brightness according to distance - assuming brightness correlates with light-energy?

No promble and yes, these effects are accounted for. The measured spectrum has a red shift. Simply remove the red shift (shift the spectrum back to the blue end by the specified amount) and integrate to get the total energy in the spectrum. This is the standard candle. There are other effects due to absorption by interstellar and intergalactic media that are also inferred/accounted for, but I don't have the details to hand...