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The transit method is a method of detecting extra-solar planets by looking for variability in a star's light that indicates a transit. It is arguably the easiest and most effective and the vast majority of known exoplanets were found using transits. The technology required is the sensitivity for precise measurement of the star's brightness (magnitude), and automation to keep watching the star. If a star dims repeatedly by the same amount with the precisely the same lengths of time dimmed and lengths of time between, the presence of an object with an orbit such that the object passes between the star and the Earth is the only viable explanation. The object can be a planet or a binary companion; the technique is also used to discover binary stars and when any repeating transit is uncovered, it is necessary to determine which of these has been found. Starspots can mimic them for a limited time but eventually lose the pattern of variation.
Automation is not strictly necessary but practically speaking, it is a major factor in the development and success of the transit method, both to operate the telescope repeatedly and to analyze the data for signs of a planet. The largest telescopes are not necessary, and surveys aiming to find planets have been successful using small telescopes. Ground telescope surveys include WASP and the MEarth Project, and space-based surveys include Kepler and TESS.