A Simple Aurora Detector
Peter Alfred Zaffo
32 Elm Street
Apartment Left
Warrensburg, New York 12885-1618
ABSTRACT
By means of an ordinary liquid-filled field compass, a small bar magnet, and some plywood, a
simple device for detecting magnetic storms can
be constructed. Magnetic storms are associated
with the occurrence of the northern (or southern)
lights, or the aurora borealis (australis). Magnetic
storms, caused by charged particles ejected from
active regions on the sun, depress the strength of
the Earth’s magnetic field, causing compass needles to show a southward deflection. The magnetometer herein described can readily detect these
magnetic storms and can be used to give several
hours’ warning of impending auroral activity.
Keywords: Apparatus; astronomy; geophysics – general.
The Aurora and Magnetic Storms
The northern lights, or the aurora borealis, is one
of nature’s most beautiful and awe-inspiring phenomena, but many people miss this celestial light
show because they do not know when to look for it.
One way to overcome this difficulty is by realizing
that magnetic storms accompany major auroral displays. Eruptions on the surface of the sun release
vast quantities of electrically charged particles into
interplanetary space. When these charged particles
come into the vicinity of Earth, the Earth’s magnetic
field deflects most of the particles past a surrounding cavity known as the magnetosphere. However,
some of the charged particles do penetrate the magnetosphere and spiral down towards the magnetic
poles of the Earth. These regions near Earth’s magnetic poles form circular areas known as the auroral
ovals. The charged particles do not travel along magnetic field lines but travel in a spiral pattern around
the field lines. Once the charged particles enter the
Earth’s upper atmosphere, they excite the gases in
the atmosphere to glow like the electrical discharge
in neon signs. (Akasofu, 1989).
In addition to causing visible auroras in the upper
atmosphere, the charged particles also generate a
magnetic field, much as an electric current in a wire
generates a magnetic field. This field is of opposite
polarity to the Earth’s magnetic field, thus temporarily weakening the strength of that field. The Earth’s
magnetic field is now said to be “depressed,” and it is
this depression that earth-bound magnetometers can
detect in order to monitor the intensity of magnetic
storms and also the aurora, since auroral activity is
related to the depression of the Earth’s magnetic field.
(Davis, 1992).
The Magnetometer Aurora Detector
An ordinary liquid-filled field compass used for
mapping or finding bearings uses a magnetic needle
to indicate the direction to the north magnetic pole.
The needle is extremely sensitive to the Earth’s magnetic field, and it will always align itself along the
geomagnetic field lines at Earth’s surface. However,
the compass by itself can only indicate the direction
of the local geomagnetic field. Even during severe
magnetic storms, this direction changes very little. Far
more important is the strength of the local geomagnetic field, which varies more significantly with magnetic storms. The compass can be made to measure
the strength of the geomagnetic field by introducing
a small bar magnet in the vicinity of the compass.
This secondary magnet, called a neutral magnet, has
its north pole pointing south or opposite that of the
prevailing geomagnetic field. By having the neutral
magnet oriented opposite the direction of the geomagnetic field, there is a point north of the neutral
magnet where the strength of the geomagnetic field
will be equal but opposite to that of the magnetic
field of the neutral magnet. The trick is to place the
compass in this neutral zone. There, the needle will
point magnetic east-west rather than magnetic northsouth. If there is a depression of the geomagnetic
field due to a magnetic storm, the compass needle
will show a southward deflection. If there is an “addition” in the geomagnetic field strength, the compass needle will show a northward deflection. Once
the aurora watcher notices a southward bend on the
compass needle, he will want to be on the lookout for
visible auroral activity.
Figure 1 shows the setup for the magnetometer
aurora detector. The compass is mounted on a plywood board with “N” at the top. The neutral magnet
is positioned with its reversed poles just south of the
compass but slightly to the left of the centerline of
the compass needle. To keep the neutral magnet from
changing direction, it is imbedded in a piece of quarter- inch rectangular plywood as shown in the figure.
The piece of wood is called the slider. The slider is in
turn situated in a slider track, as seen in the figure.
This slider track allows the slider containing the neutral magnet to move only in a north-south direction.
To operate the magnetometer aurora detector, first
remove the slider from the slider track, and place it
at least five feet from the compass mounting board.
Then, orient the compass board until the compass
needle is pointing at “N” on the compass dial. Next,
replace the slider into the slider track, and move it
back and forth until the N-pole of the needle is pointing
at “W.” The field is now canceled. Once this position
is achieved, DO NOT DISTURB THE INSTRUMENT.
Journal of Geoscience Education, v. 48, 2000, p. 127
A Simple Aurora Detector
magnetic activity. Listen for “Boulder K-index” and
note the number (0 to 9). The higher the number, the
greater the magnetic storm activity and the more depressed the Earth’s magnetic field. When the Kindex is at or near 0, set the magnetometer so the
compass needle is in the east-west direction, as
noted earlier. Check the needle regularly. If the needle exhibits a southward displacement, that means
that an electron cloud from the sun is generating a
magnetic field pointing in the opposite direction of
the geomagnetic field and that auroral activity is
moving south of the normal auroral zone. If the needle moves by more than 3 degrees south of “W,” be
on the alert for auroral sightings. If the needle
shows a northern displacement, the electron cloud
generates a magnetic field in the same direction as
the geomagnetic field, and no auroral activity should
be expected since the aurora actually retracts further
north into the polar cap at this time.
Some Suggestions
The mounting board, slider, and slider track should
be made with quarter-inch plywood and secured with
wood glue. Before mounting the neutral magnet into
the slider, check its polarity with the compass. Make
sure that the N-pole of the compass needle will be attracted to the north-facing pole of the neutral magnet. If the S-pole of the needle is attracted, reverse
the direction of the neutral magnet. Also, the neutral
magnet must be positioned south of the compass,
NOT north.
When setting up the magnetometer aurora detector, be sure there are no moving iron or steel objects
near the instrument, since such objects will attract
the compass needle and cause false readings. If
there is no way to avoid a large steel or iron fixture,
Figure 1. Sketch of the magnetometer aurora detector. Com
remove the slider from the slider track, re-orient the
pass mounted on board with magnetic north at top. Neutral
magnetometer board to magnetic north, and replace
magnet is south of compass, slightly off-center to the left.
the slider into the slider track until the needle is
Neutral magnet is moved toward compass until needle points
again east-west. This corrects for the changed magwest as shown.
netic field due to the steel or iron object. Also, keep
A 10-x hand loupe (magnifier) can be used to watch electrical appliances at least 10 feet from the instruthe tip of the needle closely. I have found it extremely ment, as these devices generate magnetic fields that
helpful to etch two parallel lines on the face of the could affect the compass needle.
The magnetometer aurora detector should be placed
compass-needle capsule. These lines are spaced at
about the same distance as the width of the compass on a small plastic table or all-wooden table free of
needle. The two etched lines serve as a reference for any iron or steel. The board on which the compass
and neutral magnet are mounted should be either
the detection of any needle movement.
Before setting up the magnetometer aurora de- thick plywood or it should be reinforced with a frame
tector, first find out what the local K-index is. This is underneath. This prevents warping due to humidity,
a magnetic index that tells the relative intensity of which otherwise could lead to spurious measurements.
I have found the aurora detector to be quite relisolar-induced magnetic activity at low and middle
latitudes. The range of the K-index is from 0 to 9. A able during some recent auroral displays visible in
K-index of 5 or higher indicates auroral activity visible upstate New York. It really keeps me on the alert for
as far south as the U.S.-Canadian border or further possible auroral activity. During a recent auroral dissouth. A reading of 0 indicates no auroral activity at play, I found that the needle moved by as much as 10
low and middle latitudes and that auroral activity degrees outside the etch lines in a southward direccan only be seen north of about 60 degrees north tion, so this instrument has proven to be quite satislatitude. To find the K-index, call the NOAA solar factory in performance. I have called the NOAA
observatory in Boulder, Colorado at (303) 497-3235, solar observatory to verify needle fluctuations correwhich gives a recorded message of solar-terrestrial lating with K-indices.
Journal of Geoscience Education, v. 48, 2000, p. 128
A Simple Aurora Detector
Acknowledgments
Thomas J. Hallinan, University of Alaska, Fairbanks,
advised me on how magnetic fields affect compass
readings.
References Cited
Akasofu, Syun Ichi, 1989, The dynamic aurora: Scientific American, May, 1989, p. 90-97.
Davis, Neil, 1992, The aurora watchers handbook:
University of Alaska Press, 219 p.
About the Author
Peter Alfred Zaffo is an atmospheric-science lecturer in upstate New York and does lectures on the
aurora borealis to audiences of the Adirondack
Mountain Club and for summer camps operated by
New York State Department of Environmental
Conservation. Mr. Zaffo also lectures on lightning
and thunderstorms in the Adirondacks.
Food for Thought
...in mathematics, the word “linear” has two distinct meanings, which it is important not to
confuse. On the one hand, one may speak of a linear function (or equation): for example, the
functions f(x) = 2x and f(x) = –17x are linear, while the functions f(x) = x2 and f(x) = sin x are
nonlinear. In terms of mathematical modelling, a linear equation describes a situation in
which (simplifying somewhat) “the effect is proportional to the cause”. On the other hand, one
may speak of a linear order: this means that the elements of a set are ordered in such a way
that, for each pair of elements a and b, one has either a<b, a=b, or a>b. For instance, there
exists a natural linear order on the set of real numbers, while there is no natural such order in
the complex numbers. Now, postmodernist authors (principally in the English-speaking world)
have added a third meaning to the word – vaguely related to the second, but often confused
by them with the first – in speaking of linear thought. No exact definition is given, but the general meaning is clear enough: it is the logical and rationalist thought of the Enlightenment and
of so-called “classical” science (often accused of an extreme reductionism and numericism).
In opposition to this old fashioned way of thinking, they advocate a postmodern “nonlinear
thought”. The precise content of the latter is not clearly explained either, but it is apparently, a
methodology that goes beyond reason by insisting on intuition and subjective perception. And
it is frequently claimed that so-called postmodern science – and particularly chaos theory –
justifies and supports this new “nonlinear thought”. But this assertion rests simply on a confusion between the three meanings of the word “linear.”
Because of these abuses, one often finds postmodernist authors who see chaos theory as a
revolution against Newtonian mechanics – the latter being labelled “linear” – or who cite
quantum mechanics as an example of a nonlinear theory. In actual fact, Newton’s “linear
thought” uses equations that are perfectly nonlinear; this is why many examples in chaos theory come from Newtonian mechanics, so that the study of chaos represents in fact a renaissance of Newtonian mechanics as a subject for cutting-edge research. Likewise, quantum
mechanics is often cited as the quintessential example of a “postmodern science”, but the
fundamental equation of quantum mechanics – Schrödinger’s equation – is absolutely linear.
Furthermore, the relationship between linearity, chaos, and an equation’s explicit solvability is
often misunderstood. Nonlinear equations are generally more difficult to solve than linear
equations, but not always: there exist very difficult linear problems and very simple nonlinear
ones. For example, Newton’s equations for the two-body Kepler problem (the Sun and one
planet) are nonlinear and yet explicitly solvable. Besides, for chaos to occur, it is necessary
that the equation be nonlinear and (here we simplify somewhat) not explicitly solvable, but
these two conditions are by no means sufficient – whether they occur separately or together
– to produce chaos. Contrary to what people often think, a nonlinear system is not necessarily
chaotic.
Alan Sokal and Jean Bricmont, 1998, Fashionable Nonsense:
Postmodern Intellectuals’ Abuse of Science: New York, Picador USA,
300 p. (from p. 143–145).
Journal of Geoscience Education, v. 48, 2000, p. 129
A Simple Aurora Detector
About The Author
Peter Alfred Zaffo is an atmospheric-science lecturer in upstate New York and does lectures on the
aurora borealis to audiences of the Adirondack
Mountain Club and for summer camps operated by
New York State Department of Environmental Conservation. Mr. Zaffo also lectures on lightning and
thunderstorms in the Adirondacks.
Figure 1. Sketch of the magnetometer aurora detector. Compass mounted on board with magnetic
north at top. Neutral magnet is south of compass,
slightly off-center to the left. Neutral magnet is
moved toward compass until needle points west as
shown.
Journal of Geoscience Education, v. 48, 2000, p. 130