AURORA
An aurora is
a natural light display that shimmers in the sky. Colorful blue, red, yellow,
green, and orange lights shift gently and change shape like softly blowing
curtains. Auroras are only visible at night, and usually only appear in lower polar regions.
Auroras are
visible almost every night near the Arctic and Antarctic Circles, which
are about 66.5 degrees north and south of the Equator. In the north, the
display is called aurora borealis,
or northern lights. In the south, it is called aurora australis,
or southern lights. How Aurora Can Be Formed?
The activity
that creates auroras begins on the sun. The sun is a ball of
superhot gases made up of electrically charged particles
called ions. The ions, which continuously stream from the sun’s surface,
are called the solar wind.
As solar
wind approaches the Earth, it meets the Earth’s magnetic field. Without
this magnetic field protecting the planet, the solar wind would blow away
Earth’s fragile atmosphere, preventing all life. Most of the solar
wind is blocked by the magnetosphere, and the ions, forced around the
planet, continue to travel farther into the solar system.
Although
most of the solar wind is blocked by the
magnetosphere, some of the ions become briefly trapped in ring-shaped holding
areas around the planet. These areas, in a region of the atmosphere called
the ionosphere, are centered around the Earth’s geomagnetic poles.
The geomagnetic poles mark the tilted axis of the Earth’s magnetic
field. They lie about 1,300 kilometers (800 miles) from the geographic poles,
but are slowly moving.
In the
ionosphere, the ions of the solar wind collide with atoms
of oxygen and nitrogen from the Earth’s atmosphere. The
energy released during these collisions causes a colorful glowing halo around
the poles—an aurora. Most auroras happen about 97-1,000 kilometers (60-620
miles) above the Earth’s surface.
The most
active auroras happen when the solar wind is the strongest. The solar wind is
usually fairly constant, but solar weather—the heating and cooling of different
parts of the sun—can change daily.
Solar weather
is often measured in sunspots. Sunspots are the coldest part of the sun
and appear as dark blobs on its white-hot surface. Solar flares
and coronal mass ejections are associated with sunspots. Solar flares and
coronal mass ejections are sudden, extra bursts of energy in the solar wind.
Sunspot activity is tracked over an 11-year cycle. Bright, consistent auroras
are most visible during the height of sunspot activity.
Some increased
activity in the solar wind happens during every equinox. These regular
fluctuations are known as magnetic storms. Magnetic storms can lead to
auroras being seen in the midlatitudes
during the time around the spring and autumnal equinoxes. Auroras have
been visible as far south as the Yucatan Peninsula in Mexico.
Magnetic storms
and active auroras can sometimes interfere with communications. They
can disrupt radio and radar signals. Intense magnetic
storms can even disable communication satellites.
Why They Can Form Difference Color?
The
colors of the aurora vary, depending
on altitude and the kind of atoms involved. If ions strike oxygen
atoms high in the atmosphere, the interaction produces a red glow. This is an
unusual aurora—the most familiar display, a green-yellow hue, occurs as ions
strike oxygen at lower altitudes. Reddish and bluish light that often appears
in the lower fringes of auroras is produced by ions striking atoms of nitrogen.
Ions striking hydrogen and helium atoms can produce blue and purple auroras,
although our eyes can rarely detect this part of the electromagnetic
spectrum.
sources:
https://www.nationalgeographic.org/encyclopedia/aurora/
http://www.aurora-service.eu/aurora-school/aurora-borealis/
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