ABSOLUTE BEGINNERS
This article featured in
the September 2000 Beginners Magazine
AURORAE
AURORAE are also known as Aurora Borealis
the Northern Lights or Aurora Australis the Southern Lights.
On a clear night the aurora is visible as waves of
coloured light moving across
the sky. Although
not common from the south of the British Isles they are quite
common in the far north of Scotland and even more common nearer
to the North Pole.
Aurorea
(the plural, Aurora singular) are caused by energetic particles
which have been ejected from the Sun, hitting the Earths atmosphere. Earth has a strong magnetic field and the particles
ejected from the Sun are also magnetic so when they hit the
Earth's magnetic field they are deflected towards rings around
the poles. As the
particles move through the upper atmosphere they ionise the
atoms and cause them to glow much like in a florescent light.
Aurorea
take many shapes and colours and move in different ways.
The main colours are red from Nitrogen and green from
Oxygen but when the show is faint colours are hard to discern
a grey glow may be all that is seen.
The colours are caused by the constituent gases in
the atmosphere being ionised depending on how energetic the
in coming particles are.
Different
shapes may occur and appear to be moving across the sky, sometimes
at considerable speed. The
most common shapes are sheets, rays and curtains.
Sheets are large areas of colour which have no discernable
pattern or movements. Rays are long straight beams
of light which move like search light beams.
Curtains are the most impressive of all and do look
like huge coloured curtains swirling across the sky.
The Colours are much more noticeable in photographs
because longer camera exposure times allows more light to
be captured and recorded on the film.
The eye can only record very brief pictures on its
own.
Aurorae
may occur at any time but are more common and stronger when
the Sun is at its peak of activity.
The Sun has a cycle of about 11 years when the number
of flares, sunspots and outbursts called mass ejections, are
more numerous and much stronger. The activity seen on the surface of the Sun is much
more violent at Solar maximum and the Sun is reaching its
maximum about now. There was a huge sun spot seen
just over a week ago which often indicates there may be mass
ejections and Aurorae. Unfortunately none were seen
over southern England this time but a couple of
months ago there was beautiful show over the whole
of Britain.