Hubble constant

As a result of this observation, Hubble concluded that the universe must be expanding, and his calculated rate of expansion became known as the Hubble constant.

Unfortunately, since Requiem was not discovered until 2019, long after it had faded from view, it was not possible to gather sufficient data to measure the Hubble constant then.

A theory with just six parameters—including the Hubble constant—Lambda-CDM precisely fits the distribution of fluctuation sizes measured by Europe’s Planck spacecraft, says Tanvi Karwal, a cosmologist at the University of Chicago.

The number that describes the expansion goes by the name "the Hubble constant," appearing in multitude of different equations and models of the Universe and its constituents.

Freedman led a collaboration in the 1990s called the Hubble Space Telescope Key Project, which calculated the Hubble constant more precisely than anyone had before.