Kepler 太空望遠鏡有什麼長處 ?
本帖最後由 mca 於 2010-1-5 14:00 編輯今天 NASA報導 Kepler Telescope 的初次發現 --- 五顆系外行星
http://science.nasa.gov/headlines/y2010/04jan_fiveplanets.htm
開普勒太空望遠鏡是專為大規模找尋系外「類地行星」(像地球可以適合生物居住的行星) 而設，在 2009 年 3 月初發射，預計壽命不少過 3.5 年。它的長處可以從官方網頁見到，藍色中文是重點翻譯。
節錄自http://kepler.nasa.gov/Mission/QuickGuide/
The Transit Method of Detecting Extrasolar Planets:
When a planet crosses in front of its star as viewed by an observer, the event is called a transit. Transits by terrestrial planets produce a small change in a star's brightness of about 1/10,000 (100 parts per million, ppm), lasting for 2 to 16 hours. This change must be absolutely periodic if it is caused by a planet. In addition, all transits produced by the same planet must be of the same change in brightness and last the same amount of time, thus providing a highly repeatable signal and robust detection method.
用「凌食」(transit) 方法找尋系外行星有很好的重複性。
Once detected, the planet's orbital size can be calculated from the period (how long it takes the planet to orbit once around the star) and the mass of the star using Kepler's Third Law of planetary motion. The size of the planet is found from the depth of the transit (how much the brightness of the star drops) and the size of the star. From the orbital size and the temperature of the star, the planet's characteristic temperature can be calculated. From this the question of whether or not the planet is habitable (not necessarily inhabited) can be answered.
從觀測資料可推算系外行星的軌道周期、行星質量、直徑和溫度，從此又得知這顆是否「類地行星」。
The Kepler 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. The fields of view of most telescopes are less than one square degree. Kepler needs that large a field 105 square degrees in order to observe the necessary large number of stars. It stares at the same star field for the entire mission and continuously and simultaneously monitors the brightnesses of more than 100,000 stars for the life of the mission 3.5 years
開普勒望遠鏡使用 0.95 米鏡來測量凌食時的光度變化，視場面積比普通設計大 100 倍以上 (相當於目視伸長手臂後的手掌面積)，並且可以同時監察 100,000 顆星。
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