|
 A
distance light source will emit light at a specific frequency and
if that same frequency is detected at the target location, we know
that the two objects are stationary relative to one another - and
the light photon did not pass by any strong gravitational fields.
If the two objects are moving away from each other - the target
will detect a slightly longer wavelength.
The redshift (z) is the change in wavelength divided by the rest
wavelength
z = (Observed wavelength - Rest wavelength)/(Rest wavelength)
Note that postive values of z correspond to increased wavelengths
(redshifts)
This is called Cosmological Red shift
So objects that are moving away from us faster appear redder.
 In
1929, Edwin Hubble announced that almost all galaxies appeared to
be moving away from us. In fact, he found that the Universe was
expanding - with all of the galaxies moving away from each other.
This phenomenon was observed as a red shift of a galaxy's spectrum.
This red shift appeared to be larger for faint, presumably further,
galaxies. Hence, the farther a galaxy, the faster it is receding
from Earth.
"The team measured the Hubble Constant to be 70 km/sec/mpc,
with an uncertainty of 10 percent. This means that a galaxy
appears to be moving 160,000 miles per hour faster for every 3.3
million light-years away from Earth. " - Nasa
"Combining Hubble's constant measurement with estimates for
the density of the universe, the team determined that the universe
is approximately 12 billion years old -- similar to the oldest
stars" - Nasa
|
Red
Shift and our expanding universe 
