- 3942 - NORTHERN LIGHTS - how are they created? - Auroras are caused by charged particles from Earth's magnetosphere and the solar wind colliding with other particles in Earth's upper atmosphere. Those collisions excite the atmospheric particles, which then release light as they "relax" back to their unexcited state.
------------ 3942 - NORTHERN LIGHTS - how are they created?
- The “Northern
Lights” are auroras. Why do they come in different shapes and
colors? Over millennia, humans have
observed and been inspired by beautiful displays of light bands dancing across
dark night skies. Today, we call these lights the aurora: the aurora borealis
in the northern hemisphere, and the aurora australis in the south.
-
- The color of the light corresponds to the
release of discrete chunks of energy by the atmospheric particles, and is also
an indicator of how much energy was absorbed in the initial collision.
-
- The
frequency and intensity of auroral displays is related to activity on the sun,
which follows an 11-year cycle. Currently, we are approaching the next maximum,
which is expected in 2025.
-
- In the 17th
century, scientific explanations for what caused the aurora began to surface.
Possible explanations included air from Earth's atmosphere rising out of
Earth's shadow to become sunlit (Galileo in 1619) and light reflections from
high-altitude ice crystals (Rene Descartes).
-
- In 1716,
English astronomer Edmund Halley was the first to suggest a possible connection
with Earth's magnetic field. In 1731, a French philosopher named Jean-Jacques
d'Ortous de Mairan noted a coincidence between the number of sunspots and
aurora. He proposed that the aurora was connected with the sun's atmosphere.
-
- The most
common source of aurora is particles traveling within Earth's magnetosphere,
the region of space occupied by Earth's natural magnetic field.
-
- Images of
Earth's magnetosphere typically show how the magnetic field "bubble"
protects Earth from space radiation and repels most disturbances in the solar
wind. However, what is not normally highlighted is the fact that Earth's
magnetic field contains its own population of electrically charged particles
(or "plasma").
-
- The
magnetosphere is composed of charged particles that have escaped from Earth's
upper atmosphere and charged particles that have entered from the solar wind.
Both types of particles are trapped in Earth's magnetic field.
-
- The motions
of electrically charged particles are controlled by electric and magnetic
fields. Charged particles gyrate around magnetic field lines, so when viewed at
large scales magnetic field lines act as "pipelines" for charged
particles in a plasma.
-
- The Earth's
magnetic field is similar to a standard "dipole" magnetic field, with
field lines bunching together near the poles. This bunching up of field lines
actually alters the particle trajectories, effectively turning them around to
go back the way they came, in a process called "magnetic mirroring".
-
- During quiet
and stable conditions, most particles in the magnetosphere stay trapped,
happily bouncing between the south and north magnetic poles out in space.
However, if a disturbance in the solar wind (such as a coronal mass ejection)
gives the magnetosphere a "whack", it becomes disturbed.
-
- ‘Magnetic
mirroring’ makes charged particles bounce back and forth between the
poles. The trapped particles are
accelerated and the magnetic field "pipelines" suddenly change.
Particles that were happily bouncing between north and south now have their
bouncing location moved to lower altitudes, where Earth's atmosphere becomes
more dense.
-
- As a result,
the charged particles are now likely to collide with atmospheric particles as
they reach the polar regions. Then, when each collision occurs, energy is
transferred to the atmospheric particles, exciting them. Once they relax, they
emit the light that forms the beautiful aurora we see.
-
- The amazing
displays of aurora dancing across the sky are the result of the complex
interactions between the solar wind and the magnetosphere. Aurora appearing, disappearing, brightening
and forming structures like curtains, swirls, picket fences and traveling waves
are all visual representations of the invisible, ever-changing dynamics in
Earth's magnetosphere as it interacts with the solar wind.
-
- The most
common are the greens and reds, which are both emitted by oxygen in the upper
atmosphere. Green auroras correspond to altitudes close to 100 km, whereas the
red auroras are higher up, above 200 km.
-
- Blue colors
are emitted by nitrogen, which can also emit some reds. A range of pinks, purples and even white
light are also possible due to a mixture of these emissions.
-
- The aurora
is more brilliant in photographs because camera sensors are more sensitive than
the human eye. Specifically, our eyes are less sensitive to color at night.
However, if the aurora is bright enough it can be quite a sight for the naked
eye.
-
- Even under
quiet space weather conditions, aurora can be very prominent at high latitudes,
such as in Alaska, Canada, Scandinavia and Antarctica. When a space weather
disturbance takes place, auroras can migrate to much lower latitudes to become
visible across the continental United States, central Europe and even southern
and mainland Australia.
-
- The
severity of the space weather event typically controls the range of locations
where the aurora is visible. The strongest events are the most rare. Get outside and witness one of nature's true
natural beauties—aurora, Earth's gateway to the heavens.
-
April 2, 2023 NORTHERN LIGHTS
- how are they created? 3942
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--- Sunday, April 2, 2023
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