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Aurora- Light of Mystery.

Extracts from this document...

Introduction

Aurora - Light of Mystery

What is aurora?image00.png

Auroras, or polar lights, are the luminous phenomenon of the upper atmosphere occurs in high latitudes of both hemispheres. Auroras in the northern hemisphere are called aurora borealis and those in the south hemisphere are called aurora australis. Aurora (Latin for ‘dawn’) is beautiful and amazing lights which are visible in the dark sky in the poles. It can appear as many different forms, but usually it is a greenish quivering glow near the horizon. In 1621 the term ‘aurora’ was coined by the French astronomer. More and more observations were done and a concrete description was archived soon afterwards. Many theories were developed this phenomenon. Some suggested that it was the reflection of sunlight of artic light and some believed it was the firelight at the edge of the world; however both hypotheses are rejected because it was found that aurora was found 100-400km above the earth surface which is well beyond the atmosphere.  Around the 17th century it has been discovered that it is caused by the interaction between energetic plasma particles from outside atmosphere with atoms of higher atmosphere. Till now, not all the questions about aurora have been answered, but with the escalating astronautic technology, we have a much better understanding on this puzzling phenomenon.

How does aurora form?

At every moment the sun is giving out charged particles in solar wind. Some of these particles are captured by the earth magnetic field and the bombardment of the solar wind with the atmospheric particles in the poles will then gives out energy as light. However this is just the

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Middle

image14.png

        For simplicity, we will consider the magnetic field only in this case. We first resolve the velocity into the parallel and perpendicular components with respect to the magnetic field. Let’s consider the each component and the Lorentz equation separately. For vpara, the velocity is parallel to the magnetic field so the angle between two vectors is zero. This makes the magnetic force on the particle caused by this velocity component zero.  Now let’s consider the perpendicular component. The angle between the magnetic field and the velocity is 90°, so the magnetic force will be greatest. This is because the largest value the sin function can give is 1 which is equal to sin (90°).

image15.png

From the equation we can see that the magnetic force is dependent on the perpendicular velocity component with respect to the magnetic field. The larger that velocity is, the larger the resultant force will be. Moreover the strength of magnitude field and the charge of the particle also affect the resultant force. F will cause v to change direction. However when v is changing, it will constantly have a perpendicular component to the magnetic field. This constant perpendicular force to the velocity will create a centrifugal force and keep the particle spinning in circle on the plane perpendicular to the magnetic field. This happens because the direction of the magnetic force changes as the velocity varies. When the charged particle approaches the magnetic field perpendicularly, it will keep on rotating on the same plane around the field, however in real life situations it is more likely that the particles will approach the field in angles rather than 90°, so the particle will travel in a spiral shape along the magnetic field. image16.pngimage17.png

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Conclusion

ix  Velocity resolving diagram. http://sprg.ssl.berkeley.edu/~cyclopi/lesson1.html

 x, xi  Steve Adams, Jonathan Allday [2000]. Advanced Physics. Oxford Press, page209

xii Magentic bottle. http://www.pjy6.org/Education/wtrapl.html

xiii Faraday’s Law. http://hyperphysics.phy-astr.gsu.edu/hbase/electric/farlaw.html

xiv  Waterloo Bridge Experiment. http://www-istp.gsfc.nasa.gov/Education/wcurrent.html

xv Birkeland current. http://www-istp.gsfc.nasa.gov/Education/wcurrent.html

xvi  Fleming’s right hand rule. www.acsinuk.freeserve.co.uk/2.htm

xvii Plasma convection. http://sprg.ssl.berkeley.edu/~cyclopi/lesson1.html

xviii Electron interaction. http://sprg.ssl.berkeley.edu/aurora_rocket/aurora/aurora15.html

xix Electron excitation. http://hyperphysics.phy-astr.gsu.edu/hbase/mod5.html

xx Colors of light. http://webexhibits.org/casuseofcolor/4D.html

Bibliography

BOOK:

Kaufmann/Comins. Discovering the universe 4th edition

Dinah L. Moche. Astronomy- a self teaching guide 5th edition

G.P. Konnen. Polarized light in Nature. Cambridge Press

Steve Adams, Jonathan Allday [2000]. Advanced Physics. Oxford Press

Kenneth R. Lang, Charles A. Whitney. Wanderers in space. Cambridge Press

Patrick Moore. The Guinness book of Astronomy. Guinness Press

JOURNAL:

James L. Burch. The Fury of Space Storm. Scientific American, 2001

Tim Beardsley. Tempests from the Sun. Scientific American, 2000

Kenny Taylor. Aurora- the grand show of light. National Geographic

INTERNET:

Rocket to the aurora. http://sprg.ssl.berkeley.edu/aurora_rocket/aurora/welcome.html

Let’s make an aurora. http://www.jsf.or.jp/sln/aurora_e/index.html

The Exploration of the Earth's Magnetosphere. http://www-istp.gsfc.nasa.gov/Education/wmap.html

Learning about Aurora. http://sprg.ssl.berkeley.edu/~cyclopi/lesson1.html

Applied physics laboratory site. http://www.jhuapl.edu/newscenter/pressreleases/1998/auroras.htm

NASA website. http://www-istp.gsfc.nasa.gov/

Web Exhibits site. http://webexhibits.org/

Britannica Online. http://www.britannica.com/

Hyperphysics. http://hyperphysics.phy-astr.gsu.edu/hbase/hph.html

Evaluation on resource:

My source information comes from books, journals and internet. The information about most topics is quite consistent except the formation of voltage drop in the aurora acceleration region. There are many theories explaining the phenomenon, but I only concentrated on the two main ones.

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