Quasar Redshift vs. Discovery Date

This plot displays the logarithm (base 10) of the number of catalogued quasars as a function of time. By the end of 1963 a handful of quasars were known. Early discoveries of quasars relied on their radio emission. The rapid increase in the number of quasars in the 1970s is due to their being identified by their optical colors. The SDSS is using the same technique to find quasars.
Image credit: Don Schneider, SDSS Collaboration

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