Aurora Borealis Revontulet

AURORA BOREALIS REVONTULET NORTHERN LIGHTS ANTTI PIETIKÄINEN

GRESIONA

ANTTI PIETIKÄINEN

AURORA BOREALIS REVONTULET NORTHERN LIGHTS

GRESIONA 1

VALOKUVAAJA PHOTOGRAPHER ANTTI PIETIKÄINEN SUUNNITTELU GRAPHIC DESIGN REIJO HIETANEN SIVUTAITTO DESKTOP MAINOSTOIMISTO GRAFU OY KUSTANTAJA PUBLISHER GRESIONA OY PAINO / PRINTED BY: JELGAVA PRINTING HOUSE COPYRIGHT© ANTTI PIETIKÄINEN & REIJO HIETANEN ISBN 978-952-93-3187-1

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NORTHERN LIGHTS Northern Lights as gusts of solar winds The Sun is the source of all life on Earth and also the origin for the Northern Lights.

The energy released from the Sun is radiated into space mainly as visible light and infrared, i.e. heat radiation. However, the Sun also emits huge quantities of elementary particles – mainly comprising electrically charged protons and electrons.

This stream of charged particles is called a solar wind. This also makes the Northern Lights.

Guided by the magnetic field The Earth’s magnetic field shields us from radiation from space and bombardment by solar winds. The Earth’s magnetic field is produced by the outer liquid surrounding the Earth’s core. The streams of metal in the core use the dynamo principle to produce billions of amperes of electrical currents that create a magnetic field far out into space.

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accelerate before ultimately colliding with atoms in the upper atmosphere.

Ionosphere is like a fluorescent lamp The uppermost part of the atmosphere, the ionosphere, starts from a height of less than 100 kilometres reaching up thousands of kilometres. In respect to the Northern Lights, the best area is located somewhere between 100 and 400 kilometres, so rather high. The boundary between Earth and outer space is generally thought to be at a height of 100 kilometres.

A significant amount of the atmosphere’s gas in the ionosphere is ionised, which means it holds free electrons and ions. An ionised gas such as this is a good conductor of electricity.

As the solar wind particles hit atoms in the atmosphere, the excited state of the atom is altered – becoming excited. Once this excited state returns to normal, the energy released is seen as light. This phenomenon is the same as, for instance, in a fluorescent lamp.

Colour from oxygen and nitrogen

The gust of solar wind flattens the Earth’s magnetic field on the daytime side and correspondingly stretches the magnetic field into a long tail on the night time side of the Earth. At the same time, the magnetic field prevents particles from accessing the atmosphere. The impact region of this magnetic field is called the magnetosphere.

The colour of the light discharges depends which element is being affected. The atmosphere mainly comprises oxygen (21%) and nitrogen (78%). The green and red colours of the Northern Lights are caused by oxygen, with violet and blue caused by nitrogen. The ultimate colour depends on the intensity of the collision.

Nevertheless, close to the magnetic Polar Regions, some particles always penetrate the magnetosphere. Being directed through the magnetic field, these particles

The most typical colours for the Northern Lights are yellowish green and violet. These colours are generated at approximate altitudes of 100 – 200 kilometres. The red col-

our is produced higher up, even at heights of 400 kilometres. As the human eye finds it difficult to identify the red colour present in the Northern Lights, the phenomenon is usually only evident during intense solar storms. In order to achieve the blue colour of nitrogen, the particles need to reach the lower parts of the ionosphere, even down the heights below 100 kilometres.

The Northern Lights oval goes around the poles The Northern Lights are seen in the Arctic, just as the Southern Lights are seen in the Antarctic. The aurora has also been seen on other planets. Here on Earth, the area of occurrence for the Northern Lights, the oval, is generally located between the 60th and 70th latitudes. If the Sun is very active, the Northern Lights can even be seen at the 50th latitude as far south as Prague in the Czech Republic.

Northern Lights can be observed throughout the winter, although sometimes visible in the summer, statistically the best months for watching the Aurora Borealis are October and March. On average, early spring in Finland is less cloudy than the autumn. The best times of the day to view the Northern Lights are during the hours around midnight.

Northern Lights are difficult to forecast Forecasting the Northern Lights is only possible for a maximum of a couple of days.

The likelihood of spotting the Northern Lights depends on the activity of the Sun and disturbances in the Earth’s magnetic field.

A lot of Northern Lights are seen when the number of sunspots quickly increases or decreases. The activity of the Sun follows an approximate 11-year cycle, which is also when there are plenty of sunspots.

The most recent peak of activity occurred in mid-2013. Intense solar bursts usually occur during these peak times, but they can occur at any time.

The SOHO and ACE satellites situated between the Earth and Sun monitor the Sun’s activity. In addition to taking images, the satellites measure the front of interference discharged from the bursts.

Following an intense solar burst directed in the correct direction, the particles can be forecast to approach the Earth in a couple of days.

Interferences in the magnetic field provide more accuracy

the Northern Lights yourself is made easier using, for instance, the Auroras Now! space weather service of the Finnish Meteorological Institute.

They do make noises after all Although plenty of people claimed to have heard the Northern Lights over the centu-

electrons hit air molocules

nights. The data collected includes data obtained from a few intense geomagnetic storms.

At the end of the research in 2011, the world’s scientific community could also confirm the sounds were made by the Northern Lights. The researchers were able to record sounds that resemble those experienced by members of the general public, which are chronologically simultaneous with the occurrence of the Northern Lights.

400 km electrons are excited

molecules give off light as they calm down

In order to be able to forecast the Northern Lights, accurate information about the state of the Earth’s magnetic field is also required. Ultimately it is the internal processes of the magnetosphere that determine whether or not the Northern Lights appear in the skies.

Indeed measuring the interference in the Earth’s magnetic field is an effective way of obtaining almost real-time forecasts of the Northern Lights. The more interference there is, the more likely the Northern Lights will appear. In Finland, predicting

ries, in the scientific community, the noises were thought to be a myth. After all, the Northern Lights are created at a height of hundreds of kilometres. Nevertheless, the truth behind this problem intrigued Finnish scientists. In a project led by Aalto University during 2000 – 2005, hundreds of public accounts were archived and precise recordings were taken from around a hundred

100 km

According to the findings of the study, the sounds are produced at an approximate height of 70 metres. Just how the sounds are made remains a mystery. A number of different noise events were heard, including clapping, crackling and muffled bangs, so there are probably more than just a single mechanism. The noises therefore are not produced where the Northern Lights are generated, rather the same interferences in the atmosphere created sound sourced close to the Earth’s surface.

The effects of the Northern Lights The Northern Lights do not have any direct impacts on humans or animals, but in space satellites and even astronauts can be at risk during violent solar storms. The solar particles can even cause significant damage to the ship’s sensitive solar panels and measurement devices.

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Even the visible aurora can damage satellites. During intense Northern Lights displays, the upper parts of the atmosphere warm and expand upwards. During these times, the satellites circling Earth at low orbit are subjected to higher air resistance, which slows them down.

In principle, any long conductor on the surface of the Earth can induce magnetic storms. However, the electrical systems are well protected, which means that the solar storms and activity of the magnetic field are rarely harmful. Nevertheless, disturbances are not totally impossible.

The biggest incident that occurred during modern times was in 1989 in Quebec, when there were widespread electricity blackouts which led to six million people having to spend a night of below-freezing temperatures without any electricity. Some astonishing stories have been told throughout history, especially with the so-called Carrington case in 1859.

Sources: On page 72

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Lähteet: Ilmatieteen laitos Auroras Now! Ursa Revontulihavaitsijoiden kotisivu Aalto Yliopisto 9.2.2012 “Revontulien äänet syntyvät lähellä maanpintaa” Tiede 1/2011 “Revontulet ääntelevät sittenkin” Tieteen Kuvalehti 11/2008 “Miksi revontulissa hallitsee vihreä valo?”

Tieteen Kuvalehti 12/2010 “Miten revontulet syntyvät?”

Tähdet ja Avaruus 3/2012 “Aurinko aktivoituu” Sources: Finnish Meteorological Institute Auroras Now! Finnish Aurora Observers’ Homepage URSA Aalto University 9 February 2012 “Revontulien äänet syntyvät lähellä maanpintaa” Tiede 1/2011 “Revontulet ääntelevät sittenkin“ Tieteen Kuvalehti 11/2008 “Miksi revontulissa hallitsee vihreä valo?“ Tieteen Kuvalehti 12/2010 “Miten revontulet syntyvät?“ Tähdet ja Avaruus 3/2012 “Aurinko aktivoituu“

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AURORA BOREALIS REVONTULET NORTHERN LIGHTS

REVONTULET Noin 2% ihmiskunnasta asuu alu­eil­la, joilla revontulet näkyvät normaalisti.

Pohjoisella pallonpuoliskolla re­ v­on­tulet (Aurora Borealis) nä­ky­ vät syyskuun alun ja huh­ti­kuun alun välisenä aikana.

Eteläisellä pallonpuoliskolla re­v­on­tulet (Au­rora Australis) nä­ ky­vät hel­mi- ja lokakuun välillä.

AURORA BOREALIS About 2% of the world’s popu­ lation lives in areas, where the Northern lights can be seen.

On the northern hemisphere, the Northern lights (Aurora Borealis) are visible between early Sep­ tember and early April.

On the southern hemisphere, the Southern lights (Aurora Aus­ tralis) are visible between Feb­ ruary and October.

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