WASHINGTON, March 6 (Xinhua) -- NASA's Kepler space telescope, the world's first mission to hunt for extrasolar Earth-like planets, lifted off on Friday night from Cape Canaveral Air Force Station in Florida.

    Its instrument is a specially designed 0.95-meter diameter telescope called a photometer or light meter.

    It has a very large field of view for an astronomical telescope-- 105 square degrees, which is comparable to the area of your hand held at arm's length. It needs a large field to observe a large number of stars.

    It stares at the same star field for the entire mission and continuously and simultaneously monitors the brightness of more than 100,000 stars for the life of the mission -- 3.5 or more years.

    The photometer must be space-based to obtain the photometric precision needed to reliably see an Earth-like transit and to avoid interruptions caused by day-night cycles, seasonal cycles and atmospheric perturbations, such as extinction associated with ground-based observing.

    Results from the Kepler mission will allow us to place our solar system within the context of planetary systems in the Galaxy.