Coronal mass ejections from the sun send high-charged particles towards the earth's atmosphere which collide with
oxygen, nitrogen and other molecules thus displacing electrons. When these electrons recombine with other loose atoms,
light is emitted which produces impressive displays across the planet's two geomagnetic poles. To be more specific, the
most common colour observed during such displays is green with tints of yellow and which have as basis the excitation
of oxygen atoms. In contrast, when nitrogen atoms are excited, one observes various shades of blue and violet displays
which are less sensitive to the human eye. Finally, excitation of nitrogen and oxygen, especially at lower altitudes,
yields displays which are rich in reds (as indicated by the example below). Of course, most auroras produce a wide
range and combination of these "primary" colours and it is not unusual, for example, to observe streams of green and
yellow flares during such a display.
Note: Athens, Greece may have a geographic latitude of 38° N but what is of actual significance is the fact that its geomagnetic latitude is 31° N. As a result, other locations may have a geographic location which is lower than Athens, they may be characterized at the same time with a higher geomagnetic latitude and, therefore, have a much greater probability of having an auroral display. For example, the southern-most tip of Florida (25° N, 80° W) is a full 13° further south than Athens and, yet, is characterized with a geomagnetic latitude of 36° N or 5° greater than that of Athens.
Note: The solar flare responsible for this auroral event was of type M-28.0. Type X flares are the strongest that can be hurled from the sun and can easily initiate planet-wide radio blackouts and long-lasting radiation storms. The intermediate M-class flares are responsible for brief radio blackout usually around the geomagnetic poles with little impact elsewhere. Finally, C-class flares are relatively minor with little to no consquences.
Note: With the image below, note that Dra is setting (top left) whereas UMa is rising with the handle at an angle of approximately 30 degrees (just right of center). The aurora was observed to range 40 degrees in azimuth (30 degrees west of north to 10 degrees east of north) and 20 degrees in altitude (starting from the horizon).
Nov 20, 2003
Nikon Coolpix 995
26 sec @ f3.3
JPG RGB Fine image format
2048x1536 image size