Auroras, also known as
northern and southern lights, or aurorae (singular:
aurora), are natural light displays in the sky,
particularly in the polar regions, and usually observed
at night. They typically occur in the ionosphere. They
are also referred to as polar auroras. This is a
misnomer however, because they are commonly visible
between 65 to 72 degrees north and south latitudes,
which place them a ring just within the Arctic and
Antarctic circles. Aurorae do occur deeper inside the
polar regions, but these are infrequent and often
invisible to the naked eye.
In northern
latitudes, the effect is known as the aurora borealis,
named after the Roman goddess of dawn, Aurora, and the
Greek name for the north wind, Boreas, by Pierre
Gassendi in 1621. The aurora borealis is also called the
northern polar lights, as it is only visible in the sky
from the Northern Hemisphere, with the chance of
visibility increasing with proximity to the North
Magnetic Pole. (The North Magnetic Pole is currently in
the arctic islands of northern Canada.) 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, as if the Sun
were rising from an unusual direction. The aurora
borealis most often occurs near the equinoxes.
It's southern counterpart, the aurora australis, or the
southern polar 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."
Auroras can be spotted
throughout the world and on other planets. They are most
visible closer to the poles due to the longer periods of
darkness and the magnetic field.
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.
Oxygen
emissions - Green or brownish-red, depending on
the amount of energy absorbed. Nitrogen emissions
- 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.
Auroras are
associated with the solar wind, a flow of ions
continuously flowing outward from the Sun. The Earth's
magnetic field traps these particles, many of which
travel toward the poles where they are accelerated
toward Earth. Collisions between these ions and
atmospheric atoms and molecules causes energy releases
in the form of auroras appearing in large circles around
the poles. Auroras are more frequent and brighter during
the intense phase of the solar cycle when coronal mass
ejections increase the intensity of the solar wind.
Information
obtained from the Wikipedia web site. Wikipedia the free
encyclopedia.
