learned an important number

I found a little video by Alt Shift X explaining the Doppler effect (or redshift with light). Nicely done.



Within it was this tiny but amazing nugget of information. To see changes in the colour of light, the relative speed differential would have to be over 5200 km/s. Less than that? Our eyes cannot detect such minute changes in the colour of light; scientific instrument can.

I've been wondering about that for a long time...

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I looked up the speed of a couple of random galaxies. NGC 2655 is moving at 1383 km/s. NGC 772: 2436.