APOD 3.5:Aurora in Alaska

The photo, taken by Todd Salat, shows a reflection of Aurora borealis over a lake in Alaska; the red part of the Aurora could only be seen with a camera (after a 20-second exposure) while the green was visible to the unaided eye. The human eye takes in light for a fraction of a second at a time but a camera shutter is left open for much longer. Auroras are created by the Sun's energetic particles, which impact Earth's magnetosphere. These particles case electrons and protons to rain down near the planet's poles, which shows in the air. The red and green are made by excited oxygen atoms. The scene from last autumn is near Anchorage, and lovely lily pads dot the lake encircled by trees. The sky annotations outline such sights as the Pleiades star cluster, and Jupiter, right above the clouds.