Monitoring All Sky for Variability1

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Abstract
A few percent of all stars are variable, yet over 90% of variables brighter than 12 mag have not been discovered yet. There is a need for an all‐sky search and for the early detection of any unexpected events: optical flashes from gamma‐ray bursts, novae, dwarf novae, supernovae, "killer asteroids." The ongoing projects like ROTSE, ASAS, TASS, and others, using instruments with just 4 inch aperture, have already discovered thousands of new variable stars, a flash from an explosion at a cosmological distance, and the first partial eclipse of a nearby star by its Jupiter‐like planet. About one million variables may be discovered with such small instruments, and many more with larger telescopes. The critical elements are software and full automation of the hardware. A complete census of the brightest eclipsing binaries is needed to select objects for a robust empirical calibration of the accurate distance determination to the Magellanic Clouds, the first step toward the Hubble constant. An archive to be generated by a large number of small instruments will be very valuable for data‐mining projects. The real‐time alerts will provide great targets of opportunity for follow‐up observations with the largest telescopes.