Click and drag to zoom into a region, double-click to autoscale, or use the options at upper right.
The Control menu offers a choice of best values for H from the Hubble Space Telescope, Sloan Digital Sky Survey, WMAP and Planck Missions, and Hubble's historic determination.
Here 1+z is the ratio of the wavelength of the light observed to the wavelength that is emitted. At low speed it is simply the ratio of the velocity of recession V to the speed of light C.
The Hubble Law is based on the observations that the more distant a galaxy, the more rapidly it is receding from us. The most distant galaxies we can see are moving away at nearly the speed of light, about 300,000 (exactly 299,792.458) kilometers per second and are at the edge of the observable universe over 13 billion lightyears away.
Velocity (V) and distance (D) are related by the Hubble Constant (H) through V = H × D. When V is in kilometers per second (km/s) and D is in millions of parsecs (Mpc), the Hubble Constant used here is 68 km/s per Mpc from cosmic background radiation measurements. The formula is simply the definition of speed, V = distance/time, where the Hubble constant is 1 divided by the time the universe has been expanding. This implies that the universe is 13.8 billion years old.