The Whole Earth Blazar Telescope (WEBT) is an international consortium of astronomers created in 1997, with the aim to study a particular category of Active Galactic Nuclei (AGN) called blazars, which are characterized by strong and fast brightness variability, on time scales down to hours or less.
This collaboration involves many telescopes observing at optical, near-infrared, and radio (millimetric and centimetric) wavelengths. Thanks to their different geographic location all around the world, the emission variations of the pointed source can be monitored 24 hours a day, with the observing task moving from east to west as the Earth rotates.
WEBT observations are often carried out in conjunction with observations at higher frequencies, from ultraviolet to gamma rays, performed by both space and ground-based telescopes. In this way, information on blazar emission over almost the whole electromagnetic spectrum can be obtained.
The multi-wavelength studies performed by the WEBT have the purpose of understanding the physical mechanisms that rule the variable emission of these celestial objects. This emission mainly comes from a plasma jet pointing closely to the line of sight, and originating from a supermassive black hole located in the core of the host galaxy.