An aurora borealis or Northern Lights is a natural light display in the northern hemisphere sky caused by the collision of charged particles directed by the Earth’s magnetic field. An aurora is usually observed at night and typically occurs in the ionosphere when immediately following eruption of solar flares and solar activity.
The southern counterpart, the aurora australis (or the southern lights), has similar properties, but is only visible from high southern latitudes in Antarctica, South America, or Australasia. Australis is the Latin word for “of the South”.
These phenomena are commonly visible between 65 and 72 degrees north and south latitudes, which place them in a ring just within the Arctic and Antarctic polar circles. Auroras do occur deeper inside the polar regions, but these are infrequent and often invisible to the naked eye.
Aurora Borealis is named after the Roman goddess of dawn, Aurora, and the Greek name for the north wind, Boreas, by Pierre Gassendi in 1621. The chance of visibility of the aurora borealis increases with proximity to the North Magnetic Pole. Auroras seen near the magnetic pole may be high overhead, but from farther away, they illuminate the northern horizon as a greenish glow or sometimes a faint red or a multitude of colors.
The Northern Lights have been displayed occasionally as far south as Arlington Heights — often with green hues.
Auroral activity for the northern hemisphere is published by NOAA at the Space Weather website — swpc.noaa.gov/pmap/pmapN.html … When light yellow, orange and red extends from the north pole all the way south to Illinois in the image there is a good chance there will be Northern Lights visible in Arlington Heights. If you want to see the Northern Lights, you should check this link when news breaks that there is a high level of solar activity.
Large magnetic storms are most common during the peak of the eleven-year sunspot cycle or during the three years after that peak.
Geomagnetic storms that ignite auroras actually happen more often during the months around the equinoxes. It is not well understood why geomagnetic storms are tied to Earth’s seasons, but it is known that during spring and autumn, the interplanetary magnetic field and that of Earth link up.
The solar wind speed is greatest — by about 50 km/s, on average — around September 5th and March 5th.
Auroras result from emissions of photons in the Earth’s upper atmosphere, above 80 km (50 miles), from ionized nitrogen atoms regaining an electron, and oxygen and nitrogen atoms returning from an excited state to ground state. They are ionized or excited by the collision of solar wind particles being funneled down and accelerated along the Earth’s magnetic field lines; excitation energy is lost by the emission of a photon of light, or by collision with another atom or molecule:
Oxygen emissions are Green or brownish-red, depending on the amount of energy absorbed.
Nitrogen emissions are Blue or red. Blue if the atom regains an electron after it has been ionized. Red if returning to ground state from an excited state.
Tromsø is a city and municipality in Troms county, Norway. The administrative centre of the municipality is the city of Tromsø.
Tromsø city is the ninth largest urban area in Norway by population, and the seventh largest city in Norway by population. It is the largest city and the largest urban area in Northern Norway.