Good to glow

摘要

High in the sky, giant ribbons of colour dance and flicker. It is a good night for aurora watchers. The strips of red turn cyan and back again as the clouds roll by. Stars twinkle in the night sky beyond. A full moon is rising above the horizon, while the crescents of another two moons arch majestically. Welcome to one of the many planets outside our solar system. More than 850 have been found so far, most by watching for wobbles in starlight or a brief dimming of their parent star. Such techniques can tell us about a planet's mass, radius and orbit. Other details can be gleaned from the handful of planets that are big enough and close enough for molecules in their atmospheres to be detected.