Astronomy Picture of the Day

Explanation: What's happening in the sky? The atmosphere over northern Norway appeared quite strange for about 30 minutes last Friday when colourful clouds, dots, and plumes suddenly appeared. The colours were actually created by the NASA-funded Auroral Zone Upwelling Rocket Experiment (AZURE) which dispersed gas tracers to probe winds in Earth's upper atmosphere. AZURE's tracers originated from two short-lived sounding rockets launched from the Andøya Space Centre in Norway. The harmless gases, trimethylaluminum and a barium/strontium mixture, were released into the ionosphere at altitudes of 115 and 250 km. The vapour trails were observed dispersing from several ground stations. Mapping how AZURE's vapours dispersed should increase humanity's understanding of how the solar wind transfers energy to the Earth and powers aurora.