What Causes the Aurora

1
What Causes the Aurora?
Some Whs? of the Aurora
1. Who in history? 2. What does it look
like? 3. Where can you see it? 4. When can
you see it? 5. Whow is it produced? 6. Where
else does it occur?
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What Causes the Aurora Who in History
BC literature seems to contain reference to
auroras 1570 woodcut clearly shows concept of
aurora Galileo named it the aurora borealis,
meaning dawn of the north Descartes
proposed aurora was caused by sunlight reflected
from ice crystals in the air at high altitude
Late 1600s Edmund Halley discovered auroral
displays are ordered by direction of magnetic
field
1731 French philosopher de Mairan suspected
a connection between aurora and return of
sunspots 1741 O. Hiorten with Graham
discovered that geomagnetic activity and aurora
are connected 1859 Carrington, sketching
sunspot group was startled by white light flare.
18 hours later one of largest magnetic storms and
aurora observed over Puerto Rico.
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What Causes the Aurora Who in History
Late 1800s suggestions that particles shot
off from sun are guided by Earth's magnetic field
to the auroral zone. (Concept re-emerges
even today on the web.) Start of modern
research First International Polar Year 1882-3,
led by Birkeland. Start of contemporary
research IGY 1957-8, led by Chapman. Nobel
prize winner Alfven
Kristian Birkeland (1867-1917)
Sydney Chapman (1888-1970)
Hannes Alfven (1908-1995)
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What Causes the Aurora What does it look like?
Views from the ground arcs and rays
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What Causes the Aurora What does it look like?
Views from the ground arcs and rays
Characteristic features sharp lower border,
colors vary with height
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What Causes the Aurora What does it look like?
Views from the ground arcs and rays
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What Causes the Aurora What does it look like?
Views from the ground corona and swirls
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What Causes the Aurora What does it look like?
View from the Shuttle, toward the horizon
Characteristic features sharp lower border,
colors vary with height
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What Causes the Aurora What does it look like?
View from space, the entire auroral oval can be
imaged
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What Causes the Aurora What does it look like?
View from space crowns of aurora over both
hemispheres
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What Causes the Aurora What does it look like?
View from space The great auroral substorm over
the Southern Hemisphere as observed with Dynamics
Explorer 1 from 0202 to 0517 UT on 13 June
1983 is shown here in a 16-image sequence.
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What Causes the Aurora Where can you see it?
The auroral oval is centered at the magnetic
north pole Geomagnetic activity determines how
low in latitude the aurora will extend.
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What Causes the Aurora When can you see it?
The peak in auroral activity slightly lags the
solar cycle.
Solar cycle
Geomagnetic activity
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What Causes the Aurora When can you see it?
Aurora of this brightness over the southern
United States might occur only once or twice per
solar cycle.
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What Causes the Aurora When can you see it?
You must be in the right place at the right time
Daily forecasts are available from
http//www.gi.alaska.edu/aurora_predict/
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What Causes the Aurora How is it produced?
Fast, hot, electrons and ions in the
magnetosphere stream toward Earth hitting the
cold atoms and molecules of our atmosphere
When it is stormy in the Magnetosphere, even more
particles stream in to make bigger, brighter
Aurora.
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What Causes the Aurora How is it produced?
Recall what happens when an atom transitions to a
higher energy state. The atom will eventually
return to its ground state and emit a photon of a
characteristic energy (color).
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What Causes the Aurora How is it produced?
Those hot, streaming magnetosphere particles
ionize or excite the atoms and molecules of our
atmosphere, which give off light when they calm
down
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What Causes the Aurora How is it produced?
The color of the light depends on what type of
particle is hit and whether it is ionized or
excited to a higher energy level.
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What Causes the Aurora Where else?
Aurora have been observed on every planet with a
magnetosphere.
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What Causes the Aurora
Contacts
Dr. Barbara Giles Code 692 Goddard Space Flight
Center Greenbelt MD 20771 (301)
286-0447 barbara.giles_at_gsfc.nasa.gov
Dr. Robert Hoffman Code 696 Goddard Space Flight
Center Greenbelt MD 20771 (301)
286-7386 robert.a.hoffman_at_gsfc.nasa.gov