ARCturus

Hunting for the Northern Lights

Feelings in a Workshop

Aurora Borealis – Measuring the Magnetic Field

The North Pole and the South Pole are the most common places where the Northern Lights can most likely be seen on Earth. In Finland they occur mainly in Lapland. However, during strong storms of Aurora Borealis it has sometimes been possible to see them even in Central Europe. In literature, there is a rich variety of beautiful legends and stories of this wonderful celestial phenomenon.

The Aurora Borealis is closely connected with the activity of the Sun. Dark regions on the surface of the Sun are called ‘sun spots’, which are areas cooler than their surroundings. Their cycle is about 11 years. The amount of the sun spots is regarded as an indicator for the activity of the Sun. The electronic particles, i.e. protons and neutrons, having their origin in the Sun, enter the magnetic field of the Earth. They collide with the molecules in the upper layers of the atmosphere (ionosphere), as high as about 80-300 kilometres. These collisions excite the molecules. They emit light when the excitation is discharged.

The best place on Earth for observing the Northern Lights is Fennoscandia. In the north of Lapland, about 200 nights a year are lit by the Northern Lights. The best moment for the observation is the so called magnetic midnight, i.e. about an hour before midnight. Most of the Northern Lights occur when the amount of the sun spots is at its highest, but also at the time of the equinoxes. It is often said that Aurora Borealis crackles and whizzes. It is true that the Aurora Borealis can be ‘heard’, but only with the help of special devices used by radio amateurs. They can listen to such frequencies that cannot be heard by using common radio devices. The reason for this kind of electromagnetic radiation is ionization, caused in the atmosphere by a flow of particles from the Sun. The result of this process can be seen in the darkness of the night: the Northern Lights.

The most common shape of the Northern Lights is a peaceful and dim curve. A belt-like shape is much more active. The lower edge of the belt is often curved with vertical rays constantly in motion. Sometimes the shape looks like a blot or a bright corona. The common colour of the Northern Lights is greenish, but also colours red or blue can sometimes be seen. If we are lucky, there may even be a chance to see the Northern Lights dancing in the sky!

It is obvious that the Northern Lights cause changes in the magnetic field. These changes can be determined with the help of various measurements. They give experimentally ”predicted” information on the occurrence of the Northern Lights. Other ways to foresee them are the observation of sun spots and the occurrence of radio interferences. It is worthwhile, every now and then, to also check on the Internet the latest information on the Northern Lights.

 

This workshop introduces two simple methods by which the changes in the magnetic field strength can be tested and measured.

A simple magnetometre

Hang a bar magnet on a piece of yarn and fix a small mirror in the middle of the magnet (see Solar System/Northern Lights). Eventually, when the magnet stops, it takes a position along the magnetic field lines. Focus a thin ray of light, for instance a laser light, at the middle of the mirror and observe the motions of the reflected ray on the wall or a screen. The bar magnet turns when the direction of the magnetic lines change. It means that the change in the position of the reflected ray is the indicator of the change in the magnetic field. If the circumstances of the experiment are not disturbed by any distraction, it is most likely that the motions of the magnet are caused by changes in the magnetic field. This being the case, there is reason to be even more eager to observe the Northern Lights.

The reliability of the results can be weakened by many factors, such as airflow, constructions in the surroundings (for instance iron tubes), electric devices and other equipment of modern technology. The research tools can be placed as far as possible from disruptive elements. The magnet hanging on a piece of yarn and the mirror can be placed inside a glass cylinder in order to prevent airflow.

Measuring electricity in the ground

Another experiment can be made in the garden, forest or marsh. The main thing is that the ground is moist. Dig two copper tubes with the length of 1.5 metres in the ground and measure the voltage between them. The distance between the tubes should be more than 100 metres. The fluctuation of the voltage may indicate a disturbance in the magnetic field, caused by the Northern Lights. Again on the following night, it is worthwhile to try and find the Northern Lights in the sky. The researchers have noticed a clear link between the disturbances in the global magnetic field and the Northern Lights.

The voltage between the copper tubes may be measured over several days. Using an amplifier, the tubes can be connected to a computer. The measured values, gathered at chosen intervals, may later be used for further processing (see Solar System/Northern Lights). With the help of modern digital technology, the results measured can be processed and shown in a form of diagrams or tables.

A text of the same topic, written by Irma Hannula, is published in the magazine Dimensio 07/2002.

 

 

 

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