Next: Splitting the change of
Up: Interpreting the spectral axis
Previous: Interpreting the spectral axis
Contents
In the first half of the twentieth century, optical astronomers noted that
a source emitting in its rest frame at a wavelength
will appear to
emit at a larger wavelength
in the observatory frame. To quantify
this phenomenon, they introduced the observational notion of redshift,
, defined with
 |
(20) |
The redshift is a positive quantity that can become extremely large. It is
straightforward to reexpress the redshift using frequency instead of
wavelength, i.e.,
 |
(21) |
Some radio-astronomers used another definition of the redshift, called
radio redshift, but this definition is now deprecated and the optical
definition of the redshift is today universally used.
The redshift is of course linked to the Doppler effect. We however stress
that the redshift is an observational quantity, independent of any
mathematical expression of the Doppler effect. This is the key point to
understand the solution of Gordon et al. (1992).
Next: Splitting the change of
Up: Interpreting the spectral axis
Previous: Interpreting the spectral axis
Contents
Gildas manager
2015-03-19