![Hubble constant Image source: Harvard University Hubble constant Image source: Harvard University](http://www.timeone.ca/wp-content/uploads/2013/03/Hubble-Constant-e1403815667374.jpg)
Classification:
Chapter: Looking Forward, Looking back
The Hubble constant is the rate of increase of a distance in space – due to expansion of space – divided by that distance. Thus it has units of ‘per second’ but, because this gives a very small number, is usually expressed in more complex units.