Powered by the Sun

The level of auroral activity is directly related to the level of solar activity. The solar wind and other solar activities blast charged particles away from the sun. The interaction between these charged particles and Earth's magnetic field produces the aurora.

The solar connection
The surface of the sun is not a quiet place, it seethes with burning gases and massive explosions that blow millions of tons of charged particles into space.

 

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Loops and arches in the corona
are giant fountains of super-
heated gas
c
lick to see larger image

Solar activity affecting the aurora:

Solar Wind:
the streams of charged particles that produce the aurora come from the corona, the outermost layer of the sun's atmosphere. The corona is exceedingly hot, measuring more than one million degrees. The high temperature causes hydrogen atoms to split into protons and electrons. The resulting gas of charged particles is called plasma, which is electrically conductive. The solar plasma is so hot that it breaks free of the sun's gravitational force and blows away from the surface in all directions. The movement of this plasma is called solar wind. The intensity of the solar wind and the magnetic field carried by it change constantly. When the solar wind blows stronger, we see more active and brighter aurora on Earth.

Helpful links:
Space Weather Guide
from NASA's Sun-Earth
Connection Education Forum

"Living in the atmosphere
of the Sun"

NASA Solar Physics page

"Sunspot cycle predictions"

Big Bear solar
observatory website

Solar and Heliospheric
Observatory web site

TRACE satellite site

thumbnail of CME
click to watch a movie of
a comet and a CME
(420 kb MPEG)

Coronal mass ejections are, as the name implies, massive explosions of the corona. Made of plasma and threaded with the sun's magnetic field lines, coronal mass ejections are responsible for gusts of solar wind. They can be very damaging if they collide with Earth. They can disrupt radio communications, damage satellites, and even be hazardous to astronauts if they are outside the spacecraft.

 


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Sunspots
click to see larger image

 

Sunspots appear as small dark dots on the sun's surface. They appear dark because they are cooler than the surrounding surface. Intense explosions often occur around sunspots which can cause "gusts" of solar wind.

Sunspot cycle: The number of sunspots on the sun's surface changes on a fairly regular cycle, which scientists refer to as the sun's 11-year cycle variation. Sunspot activity, and hence auroral activity, tends to peak every 11 years. This peak is called the Solar Maximum. The last solar maximum was in 2001, the next is expected around 2012. The chances of seeing the aurora at lower latitudes is affected by the sunspot cycle, but chances at higher latitudes are not dependent as the auroral oval is normally present.

 



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Sunspot cycle
click to see
larger image

Coronal holes: strong solar wind can also blow out unexpectedly from a quiet region of the sun. While examining the x-ray images of the solar corona, scientists discovered large dark holes referred to as coronal holes. The coronal hole, which tends to develop after the sunspot cycle peaks, can last more than 12 months. Because the sun completes one rotation in 27 days (Earth completes one rotation in 24 hours), the solar wind from the coronal hole "hits" Earth every 27 days.

coronal hole Flash movie thumbnail
Particles from a coronal hole
strike Earth every 27 days
click image to see a Flash movie (32kb)

coronal hole thumbnail
coronal hole
click to see larger image

rotating sun movie
(2447 kb MPEG)

Increased auroral activity
When the solar wind blows strong, the auroral oval becomes brighter and wider. In the sky, the aurora appears bright, active, contains more colors, and can be seen further south than normal. While a quiet aurora displays only pale green curtains, more active ones will have a pink band at the bottom edge and exceptionally strong ones will glow deep red at the top. As the auroral oval expands, the aurora can be seen further south of where it normally occurs. Throughout history, reports of the aurora appearing as a red glow in the northern sky have been recorded in countries as far south as Japan, Mexico, Iran, and Italy. In these cases, the viewers were observing the extensive red upper portion of an extremely powerful aurora.

 

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site last modified: August 2003 maintained by Asahi Aurora Web Manager