For slope of the Hubble Constant, what does the 'rise' direction represent?

Question

Distance

X axis

Y axis

Recession Velocity (RV)

Answer 1

The hubble constant measures how quickly we see distant objects in the night sky move away from us. This is measured through redshifts of the spectra of distant galaxies using the doppler effect (same way a siren sounds different when it is coming towards you vs away from you). The slope of the line of best fit of many galaxies recessional velocity or speed away from us vs distance gives you a good estimate as to how quickly the universe is expanding currently. It is somewhat of a misleading term, as the hubble constant actually changes with time due to the accelerated expansion of the universe caused by dark energy and inflation - however these effects contribute virtually no change to the parameter over the course of our lifetimes, and likely for generations to come.