Astronomy Picture of the Day

Explanation: Plowing through Earth's atmosphere at 60 kilometres per second, this bright perseid meteor streaks along a starry Milky Way. Captured in dark Portugal skies on August 12, it moves right to left through the frame. Its colourful trail starts near Deneb (alpha Cygni) and ends near Altair (alpha Aquilae), stars of the northern summer triangle. In fact this perseid meteor very briefly outshines both, two of the brightest stars in planet Earth's night. The trail's initial greenish glow is typical of the bright perseid shower meteors. The grains of cosmic sand, swept up dust from periodic comet Swift-Tuttle, are moving fast enough to excite the characteristic green emission of atomic oxygen at altitudes of 100 kilometres or so before vapourizing in an incandescent flash.