Doppler effect

[arthuryu123]

The reason why we could know planets are moving away from us or coming to us,is because according to the Doppler effect the object will occur blue shift or red shift.Can someone tell me more about Doppler effect in optics?  ex.what is the red or blue light related to?

[Fu-Kwun Hwang]

Each atom has it's own special spectrum. e.g. Hydrogen spectrum lines.

If a planet contain hydrogen atom and the planet is moving away from us,
The spectrum lines emitted from the planet will be similar to Hydrogen spectrum lines on earth.
However, all the line are shift to lower frequency (larger wavelength).
If there is a spectrum line in visible region, it will move toward red light region.
That is why we call it red shift.

[lookang]

http://en.wikipedia.org/wiki/Redshift
Absorption lines in the optical spectrum of a supercluster of distant galaxies (right), as compared to absorption lines in the optical spectrum of the Sun (left). Arrows indicate redshift. Wavelength increases up towards the red and beyond (frequency decreases).


Redshift and blue shift

[Hallenroy]

The Doppler Effect explain why a impolite driver's automobile horn appear to alter in incidence as he or she zoom by while receptiveness on it, and an sympathetic of the Doppler Effect can assist scientists create a diversity of comments concerning the world about them.

[perezelen]

movements of planet discribed by this effect.