Modern time-domain astronomy surveys often 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.[2] Due to large fields of view required, the time-domain work involves storing and transferring a huge amount of data. This includes data mining techniques, classification, and the handling of heterogeneous data.[3]
Before the invention of telescopes, transient events that were visible to the naked eye, from within or near the Milky Way Galaxy, were very rare, and sometimes hundreds of years apart. However, such events were recorded in antiquity, such as the supernova in 1054 observed by Chinese, Japanese and Arab astronomers, and the event in 1572 known as "Tycho's Supernova" after Tycho Brahe, who studied it until it faded after two years.[8] Even though telescopes made it possible to see more distant events, their small fields of view – typically less than 1 square degree – meant that the chances of looking in the right place at the right time were low. Schmidt cameras and other astrographs with wide field were invented in the 20th century, but mostly used to survey the unchanging heavens.
Historically time domain astronomy has come to include appearance of comets and variable brightness of Cepheid-type variable stars.[2] Old astronomical plates exposed from the 1880s through the early 1990s held by the Harvard College Observatory are being digitized by the DASCH project.[9]
The interest in transients has intensified when large CCD detectors started to be available to the astronomical community. As telescopes with larger fields of view and larger detectors come into use in the 1990s, first massive and regular survey observations were initiated - pioneered by the gravitational microlensing surveys such as Optical Gravitational Lensing Experiment and the MACHO Project. These efforts, beside the discovery of the microlensing events itself, resulted in the orders of magnitude more variable stars known to mankind.[10][11]
Subsequent, dedicated sky surveys such as the Palomar Transient Factory, the spacecraft Gaia and the LSST, focused on expanding the coverage of the sky monitoring to fainter objects, more optical filters and better positional and proper motions measurement capabilities. In 2022, the Gravitational-wave Optical Transient Observer (GOTO) began looking for collisions between neutron stars.[12]
^Graham, Matthew J.S.; G. Djorgovski; Ashish Mahabal; Ciro Donalek; Andrew Drake; Giuseppe Longo (August 2012). "Data challenges of time domain astronomy". Distributed and Parallel Databases. 30 (5–6): 371–384. arXiv:1208.2480. doi:10.1007/s10619-012-7101-7. S2CID11166899.
Gezari, S.; Martin, D. C.; Forster, K.; Neill, J. D.; Huber, M.; Heckman, T.; Bianchi, L.; Morrissey, P.; Neff, S. G.; Seibert, M.; Schiminovich, D.; Wyder, T. K.; Burgett, W. S.; Chambers, K. C.; Kaiser, N.; Magnier, E. A.; Price, P. A.; Tonry, J. L. (2013). "Thegalextime Domain Survey. I. Selection and Classification of over a Thousand Ultraviolet Variable Sources". The Astrophysical Journal. 766 (1): 60. arXiv:1302.1581. Bibcode:2013ApJ...766...60G. doi:10.1088/0004-637X/766/1/60. S2CID13841776.
