Executive summary by darmansjah
The aurora borealis
forms a 2,000
mile wide (3,219 km) oval over the North Pole.
ARTIC CIRCLE The northern lights, or aurora
borealis, forms in the rolling interior of the sun. the atoms that make up
solar gases are transformed into a thin stream of electrically charged
particles-protons and electrons. This stream, the solar wind, is both matter ad
energy. It continuously erupts from the sun. most of the solar wind sideswipes
the Earth’s magnetic shield, but some spirals down toward the planet’s north
and south magnetic poles, where it churns the oxygen and nitrogen in the
atmosphere. Shades of green, red, bright pink, blue, or violet appear depending
on how far from Earth the electrons and nitrogen molecules interact.
An Audience of One
Residents of Alaska, such as this woman in Anchorage, know
that the best time to view the northern lights is during long midwinter nights,
when the sun is at “solar maximum”-the period of greatest activity in the solar
cycle.
Dancing Lights
Auroral displays swirl in the skies above Alaska’s
Portage Lake and Bleik, Norway. Greenish-white is the most
typical auroral color.
Celestial Fireworks
Colliding with atmospheric gases, charged solar particles
create an infinite variety of auroral displays. Variations in altitude, type of
gas, intensity of solar wind, and position of the observer affect the
appearance of an aurora.
Explained by science
The Earth’s magnetic field forms a protective envelope
called the magnetosphere. Arriving with great force, the solar wind compresses
the front end of the magnetosphere and elongates the back end into a tail. At
the point of impact, if properly aligned, the solar wind’s magnetic field links
up from Earth. This connection produces the auroras seen on dark winter days in
the extreme north and south latitudes. As it blows by the Earth, the solar wind
peels back the planet’s field lines now linked to it. When those lines reach
the tail of the magnetosphere, they break away from the solar wind and
reconnect. Scientists still do not fully understand how, but this process of
reconnection transforms magnetic energy into kinetic energy, which then propels
electrons and positive ions into Earth’s atmosphere along the newly reconnected
field line. These speeding particles, especially the electrons, create the
nighttime auroras. Crashing into the atmosphere, electrons hit the atoms and
molecules of gases such as oxygen and nitrogen. In each collision, the atom or
molecule absorbs energy from the electron, then releases the light. Color
depends on which gas is hit and at what altitude.
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