Biography
My name is Kevin Wang, a junior studying Computer Engineering at USC. Despite not studying
astronomy, I am a big fan of astronomy because of the large amounts of information that we still
do not know about the universe. The aurora borealis is a very beautiful sight which I wish to
someday be able to see for myself.
Abstract
The Aurora Borealis is a strange miracle that exists in the sky. Named after Greek and Roman
Gods, the auroras have been researched by scientists for very long periods of time. The auroras
are caused by interactions between different particles along with the solar wind. Different types
of particles colliding with each other cause different colors and intensities of each part of the
aurora. The brightness and wavelengths of each section of the aurora have been researched by
scientists using both laboratories and computer graphics. Different particles have specific colors
and reactions when colliding with solar flares, which have been documented by scientists both in
real experiments and computer generated experiments. The sighting of auroras is usually rare,
but in certain situations, it is possible to see them from all around the world. Auroras may just be
one miracle in the sky, but by figuring out exactly how they work, it may be possible to one day
figure out other strange occurrences in the universe.
Keywords
Aurora, borealis, universe, solar flares, aurora borealis
Multimedia Suggestions
Possible suggestions include videos of auroras, and interactive things such as having different
elements react and seeing what color they make.
The Aurora Borealis
Introduction
While looking in the sky, one may see a variety of spectacles such as The Big Dipper,
Mars, comets, meteors, and even the disappointing airplane light that looks identical to a comet.
Aside from these objects that can be seen by the naked eye, there exist unique and colorful lights
in the sky that can only be witnessed in certain places around the world. These lights are called
auroras, with the most prevalent one being the Aurora Borealis in the North Pole. Different
elements in the atmosphere interact at night to form mystifying illusions. The magnificent
Aurora Borealis exists due to many chemical reactions formed from the collision of electrons and
ions. These collisions cause light particles to be released, making intricate mirages in the sky.
There is abundant research in chemistry and physics capable of explaining the phenomenon.
While the average person is unlikely to see the Aurora Borealis, years of research and
experimentation has allowed mankind to understand much more about the miracle.
The Aurora Borealis
The famous Aurora Borealis can be seen during “certain times of the year, at the polar
zones of Earth,” according to Christopher T. Bacon, the publisher of the Encyclopedia of Time:
Science, Philosophy, Theology, & Culture[1]. Named after both the Greeks and Romans, the
Aurora Borealis comes from the combination of “the Roman goddess of the dawn, Aurora” and
the Greek God of the North Wind Boreas [1]. Another aurora of a similar nature exists in the
Southern Hemisphere named after “the Latin word for “of the South” or “aurora australis”[1].
Being able to catch a glimpse of the aurora is a marvelous feat as it is difficult to reach the poles
of the Earth during the certain periods of times that they appear. As described by N. A. Staples to
a nature journal written in the 1870s, the aurora happens over the span of the nighttime, varying
in its intensity based on the different times of the night and days that Staples was observing. He
notes that “the same person” observing “the Aurora of the 24th” compared to him, who observed
“the Aurora of the morning of the 25th” got different variations in brightness [2]. Why do these
intensities vary? There is a lot of science to explain the phenomenon.
Physics of the Aurora
The emission of auroras and how brightly they shine in the night sky can be attributed to
their chemical properties. In the trade publication “Simulating the Aurora Borealis,” scientists
from the University of Utah, Calgary, and North Carolina worked together to gather lots of
information about Aurora Borealis and auroras in general. The main cause of the auroras comes
from the Sun and its ability to produce “solar flares and coronal mass ejections”, which combine
to become “solar wind” that “interacts with the Earth’s magnetic field” to form “a plasma sheet
on the side of the Earth opposite to the Sun” [3]. After these solar flares interact with the
magnetic fields, the electrons that come from the solar flare collide with particles that may have
been in the atmosphere as they traveled into Earth, causing a state of excitement for the
electrons, hence emitting a photon which is a particle of light. The combination of many of these
particle collisions allows for a large number of photons to be emitted, thus creating a stream of
light that can be observed by viewers. Although this explains the reasoning behind the emission
of light, it does not explain why the auroras are able to exist in many different colors and varying
intensities. This is where the physics comes in. These factors are explained through the different
wavelengths of the photons that are emitted into the air. Through the combination of the graph
and the photograph in figure 1 [3, Figure 1(right)][4, Figure 1(left)], it is easier to see the
reasoning behind the varying intensities and colors.
As shown in figure one, the higher altitude portions of the aurora seem to be much
dimmer compared to the portions that are slightly lower. Not only are they dimmer, they have a
longer wavelength, meaning they are more inclined to the red and violet section of the
electromagnetic spectrum. According to the trade publication, there seems to be a direct
relationship between the intensities of the sections of the aurora versus the energy given by the
electrons that are located in that section of the atmosphere [3]. The intensity of the aurora is
higher in the range between 100km and 150km meaning that there is much more energy from
electrons within that certain range of the sky. Without going into detail about the
experimentation involved with figuring out the reasoning of the wavelength change, it is
reasonable to assume that there exist different elements and particles in the sky which cause a
difference between colors of the aurora. In the article written by Erik Blixt, Joshua Semeter, and
Nickolay Ivchenko, the borealis is described as “collisions between charged particles from the
magnetosphere” along with gases such as oxygen, nitrogen, and ozone” [5]. These different
elements have been the subject of experimentation and simulation.
Simulating Auroras
Through the improved knowledge of auroras, scientists are able to more accurately depict
the aurora in the confines of a laboratory, where a smaller model of the actual phenomenon is
able to be examined more closely. By using a computer program, scientists from University of
Utah, Calgary, and North Carolina were able to accurately map auroras through a complicated
process involving both marking the locations of electrons in a certain location and rendering
colors using integrals and matrix math. The first step of the simulation requires the wavelength
of a certain portion of the aurora to be simulated. In order to simulate an aurora onto a computer,
there needs to be three different values of the color, namely red, blue, and green. In order to do
this, the "spectral tristimulus values" in the "auroral emissions, x(wavelength), y(wavelength),
and z(wavelength) need to be multiplied with a matrix that contains "SMPTE chromacity values"
[3]. These values are important because they are necessary for generating accurate color values
for the computer. After that, the integral of these values are multiplied with a function containing
the "spectral curve", the specific red, green, and blue values needed by the computer are able to
be obtained, and transformed into one specific color of a section of the simulated aurora [3].
Through constantly comparing the results of the simulated aurora with the actual aurora seen in
the sky and changing it as necessary, the scientists were able to get an algorithm that was able to
simulate and create images of auroras that were close to the actual image which one would see in
the night sky during the occurrence [3]. With constant experimentation and advanced computer
programs, scientists are able to get a better idea of the exact physics behind the different colors
and wavelengths of the aurora.
Aside from this group of researchers being able to render the aurora, two scientists named
J. C. McLennan and G. M. Shrum from the University of Toronto were able to simulate a green
aurora inside of their laboratory. These scientists created an experiment that involved using
discharge tubes and a spectrogram in order to cause collisions of different gases and see what
sort of spectral lines would emerge. These tubes were “1 inch in diameter and 30 feet long”, with
“a liquid-air jacket” which helped the tube cool down the different elements that were placed
inside the tube “to liquid-air temperatures.” Simply using that tube was not enough, so the
scientists added “an oxide-coated platinum filament” that helped the experiment with the actual
production of light similar to that of the aurora [6]. This filament was required in the experiment
because with such a small tube, it would be difficult to really notice what kind of lights was
being emitted. The filament would be used as an amplifier of the electron emission in order to
give the scientists a much better image. By mixing together different elements such as helium
with oxygen, helium with nitrogen, helium with oxygen and nitrogen, as well as neon and
oxygen, the tubes were able to emit lights of different wavelengths and intensities. Through the
comparison of the experiments and spectacle of the real aurora, it was possible to estimate what
types of elements existed in the atmosphere where the aurora was visible [6]. According to the
experiments that the University of Toronto scientists McLennan and Shrum conducted, there
seemed to be abundant amounts of helium and hydrogen as well as a much smaller amount of
oxygen in the locations of the aurora. The combination and collision of electrons in these
elements may be the reason that people are able to see the Aurora Borealis as well as other
auroras [6]. By retrieving estimates of the composition of auroras, it may be easier for people to
both see and simulate the beautiful auroras that normally can only be seen in the North and South
Pole.
The Widespread Auroras
While the Aurora Borealis may be the most prominent and visible in the North Pole, it is
not impossible for one to be able to spot a glimpse of the northern lights or some different aurora
in a location elsewhere. On February 4th of 1872, the Aurora Borealis was able to be seen in
many different locations around the northern hemisphere due to its spectacular increase of
intensity on that night. G. E. Preece, author of “Earth currents, and the Aurora Borealis of 4th
February,” combined many of the different reports of aurora sightings on that day into a journal
document in order to get different perspectives on what people around the country were able to
see during the aurora’s surprising sighting. On that day, the magnetic currents of Earth were very
intense, long and “universal in its effects,” which culminated to the effect that people around the
world to see the aurora from their backyards [7]. Compiled in the chart below named Figure 2
[Figure 2, 7] is a list of the different locations that had the aurora in their skies.
Location
Description
Duxbury, USA
"12am to 5am... Aurora visible all night"
Saint Pierre, USA
"During...[the] Aurora, a terrible snow storm"
Toronto, Canada
"Extraordinary atmospheric electrical disturbances"
Hearts Content
"Earth currents very strong on cable"
Valentia Cable Diary
"Earth currents became very strong"
Kew Observatory
"Declinometer decreased...oscillations violent"
Liverpool, Great Britain
"Powerful earth currents on every wire"
Paris, France
"phenomenon successively came nearer Paris"
Malta
"Electrical disturbances...[while]Aurora was visible"
Figure 2. Few locations that noted the aurora with reports. List compiled from [7].
Figure 2 shows a list of a few of the many different locations compiled by Preece along with
some of the text describing what the observer was able to notice during the time of the aurora.
Locations in the table, along with other countries such as Turkey, Bombay, and Persia were able
to see the huge effect of the aurora on that day, which resulted in great disturbances with
electrical wires and cables due to the character of the aurora being caused by the interference of
Earth’s magnetic field [7]. According to Christopher T. Bacon,these auroras are caused by
“heavy magnetic storms” which “relate directly to the 11-year sunspot cycle” in which the
strongest time of the cycle occurs at the peak [1]. Because these cycles occur every eleven years,
it is possible that there would be powerful auroras that can be seen around the world around the
time of the peak of each cycle. In Bacon’s report, the “Carrington-Hodgson white light solar
flare… emitted on September 1, 1859”caused a huge aurora that was able to be seen “across the
United States, Japan, Australia, and Europe” [1]. This flare occurred in 1859, which was about
twelve and a half years before the huge aurora seen on February 4, 1872. Similar to reports made
by people in the 1872 aurora sighting, the same observations that heavy interference regarding
cables were made in the 1859 aurora sighting.Both of these sightings were able to improve
scientist knowledge about this phenomenon.
Conclusion
Constant experimentation and research has allowed scientists to learn more about the
mysterious sheets of color in the sky. The universe holds many unknown wonders. In time,
scientists may be able to figure out more about both the auroras and the universe. Wonders like
solar flares, magnetic poles, and atmospheric particles are connected in strange ways. By looking
more into the auroras on the poles of the Earth, it is possible for scientists to discover answers
about mysteries related to auroras.
References
[1]Bacon, Christopher T. “Aurora Borealis.”Encyclopedia of Time: Science, Philosophy,
Theology, & Culture. Ed. H. James Birx. Thousand Oaks, CA:SAGE Publications, Inc,
2009. 65-66 SAGE knowledge.Web. 24 Feb. 2014.
[2] Staples, N. A. "Aurora Borealis." NATURE (1870): 451. Web. 28 Feb. 2014.
[3]Baranoski, G.V.G.; Rokne, J.G.; Shirley, P.; Trondsen, T.; Bastos, R., "Simulating the aurora
borealis," Computer Graphics and Applications, 2000. Proceedings. The Eighth Pacific
Conference on , vol., no., pp.2,432, 2000
[4] Alexeff, I.; Parameswaran, S.M., "The Aurora Borealis in Southern USA," Plasma
Science,IEEE Transactions on , vol.33, no.2, pp.500,501, April 2005
[5] Blixt, E.M.; Semeter, J.; Ivchenko, N., "Optical flow analysis of the aurora
borealis," Geoscience and Remote Sensing Letters, IEEE , vol.3, no.1, pp.159,163, Jan. 2006
[6] McLennan, J. C., and G. M. Shrum. "On the origin of the auroral green line 5577 Angstrom,
and other spectra associated with the Aurora Borealis." Proceedings of the Royal Society
of London. Series A 108.747 (1925): 501-512
[7]Preece, G.E., "Earth currents, and the Aurora Borealis of 4th February," Telegraph Engineers,
Journal of the Society of , vol.1, no.1, pp.102,114, 1872