The Kepler Space Telescope looking for alien life

In one passage of an extrasolar planet in Earth's size at the Space Telescope darkening of the order of one tenth per thousand is expected (for the earth and sun 0.084 ‰). This is done at a central passageway in front of the image of the star for a period of about half a day (for the Earth and Sun 13 hours). Is not the central passage, then the time of darkening is shorter. If the same change in brightness of this star repeated twice and the two intervals are equal, a planet adopted at a fixed orbit and is considered as a cause discovered. Thus determined from the orbital period and the change in brightness can be determined in accordance with Kepler's laws of the orbit and size of the terrestrial planets. Accordingly determined by the distance of the exoplanets discovered to its sun and the temperature of the sun (according to spectral type and luminosity class), the temperature on the planet and its habitability potential can be calculated approximately. Due to the different orbital inclinations of planets against our line of sight, however, occurs only at a fraction of Earth-like planet is observable from the direction of our coverage. The probability that such a transit can be observed from Earth reveals itself simply as the ratio of stellar and planetary orbital radius, in the case of earth and sun that is 0.465%