the more traditional measuring of redshift comes form using a prism or diffraction grating. Each wavelength of light is deflected from the original path by a specific angle. By carefully measuring the angle of deflection you can very precisely measure the wavelength of the light.<br /><br />To get the redshift, you compare the measured wavelengths of each portion of the spectral pattern of an element (say hydrogen) and compare that, to the position of the pattern when viewed in a labratory setting (i.e. you know it isn't moving). The difference between the two wavelength measurements (observation, and labratory) is related to the redshift.<br /><br />Now, the specific details on how this is done, depend on the device (old photographic plates, spectrographs, multi-spectrum analyzers, CCD cameras, etc). <div class="Discussion_UserSignature"> <p align="center"><font color="#c0c0c0"><br /></font></p><p align="center"><font color="#999999"><em><font size="1">--------</font></em></font><font color="#999999"><em><font size="1">--------</font></em></font><font color="#999999"><em><font size="1">----</font></em></font><font color="#666699">SaiphMOD@gmail.com </font><font color="#999999"><em><font size="1">-------------------</font></em></font></p><p><font color="#999999"><em><font size="1">"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- </font></em></font><font size="1" color="#999999">The Tenth Doctor, "Blink"</font></p> </div>