Left: Proton flux measurements made by the GOES 13 satellite detect an increase in solar particles near Earth (the red line) starting at approximately 15:00 UT (10 am EST), Aug. 3. Right: Both GOES 11 and GOES 13 detect a rapid fluctuation in the magnetic field surrounding Earth at approximately 18:00 UT (1 pm EST). Credit: NOAA/Space Weather Prediction Center Where there's a geomagnetic storm, a light display is sure to follow.
Known as the Auroral Borealis (the "Northern Lights," focused around high latitudes in the Northern Hemisphere) and the Aurora Australis ("Southern Lights," around high latitudes in the Southern Hemisphere), these spectacular light displays are caused when energetic particles from the sun (mainly protons) stream into our magnetosphere.
If the conditions are right - and in today's case, the conditions seem to be ideal - these protons will collide with Earth's atmospheric gases, generating light.
At the time of writing, aurorae have been spotted over Denmark, Norway and Germany.
Due to the magnetic configuration of our magnetosphere, the field lines enter the Earth's crust around the poles. These descending field lines funnel the solar protons from the CME into a "crown" surrounding the North and South Poles. This crown is known as the "auroral oval."