Is Hubbell's Constant really constant?

Answer 1

We used to jokingly call it the Hubble Variable because it was always being revised. It is an empirical relationship between Doppler shift and the distance of remote galaxies. We can measure the Doppler shift easily but we need some independent way of measuring the distance of at least a few galaxies to calibrate the constant.

Answer 2

No, it changes as the universe expands due to the curvature of space time and our relative distance from other celestial objects. However, the value of this constant has changed very little since Hubbell found it nearly 60 years ago.