Topic summary

Hubble constant

Extracted from the Wikipedia article Hubble's law.

Dimensionless Hubble constant

Instead of working with Hubble's constant, a common practice is to introduce the dimensionless Hubble constant, usually denoted by $h$ and commonly referred to as "little h", then to write Hubble's constant $H 0$ as $h \times 100 km\cdot s \cdot Mpc$ , all the relative uncertainty of the true value of $H 0$ being then relegated to $h$ . The dimensionless Hubble constant is often used when giving distances that are calculated from redshift $z$ using the formula $d \approx ⁠ c / H 0 ⁠ \times z$ . Since $H 0$ is not precisely known, the distance is expressed as:

Wikipedia source