How to Measure the Recession Vulnerability of a Galaxie

The more light you can gather from that galaxy in the broader the spectrum. You get like a better handle. This is why for example recent images from the James Webb Space Telescope of very very distant galaxies have a lot of uncertainty in their recession velocity because they haven't measured a whole lot of light yet and they don't have a very long curve. If they point Hubble at it and they get like a longer spectrum and more light they'll get a better measurement of that recession velocity. And so this method tells you the relative velocity of those stars in those galaxies. But that doesn't tell you like where it is or how far away it is from you.