(continued from Part 2)

The Hubble Constant

Where does the figure of 71 km/s/Mpc for the Hubble constant come from? There are a multitude of methods for measuring distance. If we can calculate the distance to an object, we already have a measure of expansion due to red shift, then we can make a stab at what the Hubble constant is. Why find the Hubble constant? If we can confirm a figure for at what rate the universe has been expanding, we can, by working backwards,...

(continued from Part 1)

Cosmological redshift

'In the early part of the 20th century, the first measurements of redshifts outside the milky way were made. The redshifts were interpreted as due solely to the Doppler effect but later Hubble discovered a rough correlation between the increasing redshifts and the increasing distances of galaxies. It was realized that these observations could be explained by a different mechanism for producing redshifts. Photons propagating...

There appears to be four types of redshift in cosmology- doppler, relativistic (which is simply a refinement of the doppler effect over larger distances), cosmological & gravitational. This blog looks at the first three and their range (gravitational redshift is looked at in this blog)-

Redshift

When heated, each element is capable of absorbing photons at a specific wavelength in the light spectrum and re-emitting them in a different direction, which means when...