Monitoring all sky for variability

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.