text: Comparing the rest-frame magnitude of objects with different values of this quantity is possible using K- correction.
full_question: Comparing the rest-frame magnitude of objects with different values of this quantity is possible using K- correction. One can identify objects with a high value for this quantity by recognizing that photons with wavelength less than 1216 angstroms are absorbed by the IGM, which gives rise to the Lyman-break method. Astronomical surveys that measured this quantity include 2dF and DEEP2. The linear version of Hubble's law, where radial velocity equals the Hubble constant times distance, only applies to objects whose value for this quantity is much less than 1. This numerical quantity indicates how distant and old an object is. For 10 points, name this numerical representation of how much an object's spectrum has been shifted to longer wavelengths.
first_sentence: Comparing the rest-frame magnitude of objects with different values of this quantity is possible using K- correction.
raw_answer: redshift [or z]