A Quasi-stellar source (Quasar) is a powerfully energetic and distant galaxy with an active galactic nucleus. Quasars were first identified as being high redshift sources of electromagnetic energy, including radio waves and visible light, that were point-like, similar to stars, rather than extended sources similar to galaxies.

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While there was initially some controversy over the nature of these objects — as recently as the early 1980s, there was no clear consensus as to their nature — there is now a scientific consensus that a quasar is a compact region 10-10,000 times the Schwarzschild radius of the central supermassive black hole of a galaxy, powered by its accretion disc.

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This program contains four dozen of the closest bright quasars and is based on a list compiled by Steven Aggas.