What causes the Northern Lights?
The Northern lights, or aurora borealis, are light displays in the skies that can be seen in the Northern Hemisphere especially near the Earth’s North Magnetic Pole. Currently the Pole is located in the arctic island regions of Canada, approximately 1000 miles from the geographic North Pole. They may appear green, red, bluish-red, or a combination. Often seen as shimmering sheets of light, like a curtain, they can also be seen as a glow on the horizon. In a similar fashion, aurora australis is visible from the Southern Hemisphere near the Southern Magnetic Pole.
Auroras are caused by caused by collisions of gas particles with charged particles (electrons and protons) shooting from the Sun and carried on the solar wind. When they reach Earth, most are deflected by the Earth’s magnetic field, but many find their way into our atmosphere where the field is weakest near the Poles.
They then collide with oxygen, nitrogen, and other gases in the ionospheric level of Earth’s atmosphere. These collisions are what produce the Northern Lights.
The most common color of aurora is yellowish green; this is caused by collisions with oxygen particles about sixty miles above Earth’s surface. Nitrogen collisions give off blue or purple-red aurora. At the higher altitude of 200 miles or so, oxygen collisions causes a somewhat rare red aurora.
The science behind this is that it takes oxygen approximately three-fourths of a second to emit green light and up to two minutes to produce red light. Upon emitting green light, the particle undergoes more collisions that change its state so that red is not produced. Up in the higher altitudes, there are far less particles to collide with, and oxygen has time to emit the red glow as described.
Aurora brightness and longevity in the sky seem to coincide with sunspot cycles, when massive plumes of ions are emitted from the Sun. This was suspected as far back as the 1800s, but was proven to be true in the late 1950s.
Geomagnetic storms also form around the time of Earth’s equinoxes, although it is not known how or why these storms occur at times of the Earth’s seasons when there is no apparent change to the Magnetic Poles.
In addition to Earth’s Northern Lights, auroras have been observed on both Jupiter and Saturn by the Hubble Telescope. The mechanism of their formation is like that of Earth’s: charged solar wing particles colliding with gas molecules in the atmosphere.