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| Aurora Borealis - Tromso Norway - Canon 400D DSLR =18-55mm EOS lens at F3.5, f=18mm. ISO 1600 - Archie Mendes 2011 |
“Galileo Galilei (1564-1642) saw the ‘Northern Lights’ from
Italy and called them ‘Boreale Aurora’ or ‘dawn of the north’ this was because
from Italy the lights were usually seen as red and always to the north. In the far north the aurora are not associated
with dawn, they can appear at any time of night, and are usually
yellow-green. In 1621, the well known astronomer
Pierre Gassendi - observing the ‘Northern Lights’ from Paris, turned Galileo’s
words about face and called them ‘Aurora Borealis’.
The Aurora Borealis or Northern Lights have intrigued
mankind for millennia. Aristotle
described the Aurora as ‘Meteron’ which roughly translates as ‘something
appearing in the air’ and my favourite- the allegoric description ‘Capre
Saltanti’ translating as ‘jumping goats’. Sir Edmund Halley (1656-1742) believed they
were controlled by the Earth’s magnetic field while the French scientist – Jean-Jacques d'Ortous de Mairan (1678
–1719) claimed they were the result of interactions between the atmospheres of
the Sun and Earth.
From a book written in AD1250 and albeit after the end of
The Viking Age (AD800 – AD1100), the ‘Old Norse’ word for the ‘Aurora Borealis’
is ‘norðrljós’. The pagan Vikings believed the ‘Northern
Lights’ were the gateway to Asgard the home of their gods.
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| 'Bivrost' - The bridge between earth and sky or 'reflections of shoals of herring'? - Reykavik 2017 - Canon 600d DSLR EOS 18-55 lens at F3.5, f=18mm. ISO 1600, 5 sec exp.- Kurt Thrust 2017 |
Following in the footsteps of: F.C. Meyer (1697-1729), Jean Baptist
Biot (1774-1862), Christopher Hansteen (1784-1873), Anders Jonas Angstrom
(1814-1874), Carl Fredric Fearnly (1818-1890) and Karl Selim Lemstrom (1838-1904), the Swedish scholar
Kristian Olaf Birkeland (1867-1917) promoted the idea that the ‘Northern Lights’
were formed when high energy, so called cathode rays’ that were emitted from
the sun were caught in the earth’s magnetic field and forced towards the earth’s
atmosphere in the polar regions. He believed that these ‘cathode rays’ or
electrons as we now call them, and the atoms and molecules of atmospheric gases
interact to create the aurora in two luminous rings one around each pole.
Birkeland was so convinced by this idea that as a demonstration experiment, he
created a chamber from 10 cm. thick glass from which was evacuated as much air
as was possible with the technology available 100 years ago. Inside the chamber
was a centrally suspended metal sphere containing an electro-magnet. A high electric charge was established between
the sphere and a cathode positioned in one corner of the chamber. The electrons
emitted from the cathode were caught in the magnetic field around the sphere
and forced to move towards the surface in the polar regions of the sphere.
Through adjustments of the voltage and the electro magnet he was able to create
two parallel rings around the sphere, just like the aurora and as his theory
predicted. When I first saw the Aurora
from Norway, a working model of his apparatus was on display in the Science
Museum at Tromso.
The driving force behind the aurora is the sun. The 'lights' are created by the interaction of the solar wind with the earth's magnetic field and the atoms of gas in the upper atmosphere. When the sun is active – lots of sunspots and
coronal eruptions of charged particles, the aurora puts on dramatic displays of
moving luminosity and colour. The green and red colours are associated with excited oxygen
atoms and blue with excited nitrogen.
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| Aurora Borealis - Tromso Norway - Canon 400D DSLR =18-55mm EOS lens at F3.5, f=18mm. ISO 1600 - Archie Mendes 2011 |
The Sami peoples, who herd their reindeer under Scandinavian skies,
have more than one word in their language for the aurora but the most commonly used is ‘guovsahas’-
meaning ‘the audible lights’. Having seen them ‘dance’ across the sky I swear I
also heard the flutter of the changing colours. There is however no real
evidence that the aurora creates sound waves.
As the ‘Northern Lights’ occur at an average height of 105 km above the surface
of the earth there is probably insufficient air to enable sound waves to form.
My favourite explanation for the ‘Northern Lights’ may be found in Danish Folklore where it was
said that the lights were the result of wild swans flying too far to the north
and becoming frozen in ice. Each time they lifted their wings in an attempt to
free themselves, the reflections from their wings caused the ‘Northern Lights’
to shine”. Archie Mendes - visiting astrophysicist at the Jodrell Plank
Observatory.
For a modern easy to read scientific explanation of the aurora folow the link to David P Stern's paper:
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