The primary purpose of a quasar catalog is to provide a comprehensive list of all known quasars, allowing astronomers to study their properties, distribution, and evolution.

The Palomar Observatory Quasar Catalog (POSS-QSO) is not a well-known quasar catalog, unlike the SDSS-QSO, 2MASS-QSO, and BQS, which are widely used in quasar research.

The SDSS-QSO is significant because it is the largest and most comprehensive quasar catalog, providing accurate positions, redshifts, and detailed spectroscopic data for a vast number of quasars.

A quasar catalog typically provides information about the positions, redshifts, and luminosities of quasars, allowing astronomers to study their distribution, distances, and energy output.

The Hamburg/ESO Quasar Survey (HES) is known for its focus on high-redshift quasars, providing valuable insights into the early universe and the formation of quasars.

The main power source of quasars is the accretion of matter onto a supermassive black hole at the center of the quasar, releasing enormous amounts of energy.

The FIRST Bright Quasar Survey (FBQS) is known for its multi-wavelength coverage, including radio data from the FIRST survey, providing insights into the radio properties of quasars.

Quasars are extremely luminous objects, with luminosities orders of magnitude greater than the luminosity of a typical galaxy.

The ROSAT All-Sky Survey Bright Quasar Survey (RASS-BQS) is known for its focus on X-ray-selected quasars, providing insights into the X-ray properties and high-energy emission of quasars.

Quasars are compact objects, with sizes much smaller than the size of a typical galaxy, typically ranging from a few light-years to a few hundred light-years.

The WISE All-Sky Survey Quasar Catalog (WISE-QSO) is known for its focus on infrared-selected quasars, providing insights into the infrared properties and dust content of quasars.

Quasars are typically found at very high redshifts, with the majority having redshifts greater than 3, corresponding to distances of billions of light-years.

The FIRST Bright Quasar Survey (FBQS) is known for its focus on radio-loud quasars, providing insights into the radio properties and jet activity of quasars.

The typical lifetime of a quasar is estimated to be a few hundred million years, during which time it undergoes significant changes in its luminosity and properties.

The Cosmic Lens All-Sky Survey (CLASS) is known for its focus on gravitational lensing studies, utilizing quasars as background sources to study the properties of dark matter and the large-scale structure of the universe.