A photometric redshift is an estimate for the distance of an astronomical object, such as a galaxy or quasar, without measuring its spectrum. The technique uses photometry (that is, the brightness of the object viewed through various standard filters, each of which lets through a relatively broad passband of colours, such as red light, green light, or blue light) to determine the redshift, and hence, through Hubble's law, the distance, of the observed object. The technique relies upon the spectrum of radiation being emitted by the object having strong features that can be detected by the relatively crude filters.