Time-domain astronomy

Time-domain astronomy is the study of how astronomical objects change with time. Though the study may be said to begin with Galileo's "Letters on Sunspots", the term now refers especially to variable objects beyond the Solar System. This may be due to movement or changes in the object itself. Common targets included are supernovae, novas, flare stars, blazars and active galactic nuclei. Visible light time domain studies include HAT-South, the Large Synoptic Survey Telescope, PanSTARRS, SkyMapper, the Wide Angle Search for Planets and the Catalina Real-time Transient Survey.
In radio astronomy the LOFAR is looking for radio transients. Radio time domain studies have long included pulsars and scintillation. Cherenkov Telescope Array, eROSITA, AGILE, Fermi, HAWC, INTEGRAL, MAXI, Swift Gamma-Ray Burst Mission and Space Variable Objects Monitor will look for transients in X-ray and gamma rays. Gamma ray bursts are a well known high energy electromagnetic transient.
Time domain astronomy uses robotic telescopes, automatic classification of transient events, and rapid notification of interested people. Blink comparators have long been used to detect differences between two photographic plates, and image subtraction became more used when digital photography eased the normalization of pairs of images. Time domain work involves storing and transferring a huge amount of data. This includes data mining techniques, classification, and the handling of heterogeneous data.
Historically time domain astronomy has come to include appearance of comets, and cepheid variable. Old astronomical plates exposed from the 1880s through the early 1990s held by the Harvard College Observatory are being digitized by the DASCH project.
Other causes of time variability are asteroids, eclipses, microlensing, planetary transits, and variable stars.