Norway December 27, 2005 imaged by Geir Øye (site,
Tall curtains of colour silently shift and alter across the night sky.
Their green base is somet 90-100 km (56-62 mile) high, the red
extends much higher. Image ©Geir Øye,
shown with permission.
occur in two ovals encircling the magnetic poles.
Canada, northern USA, Scandinavia and northern Russia
are well positioned for aurorae. The ovals expand
during high auroral activity and mid latitude Europe
and the US then see displays.
The aurora or 'Northern lights' is one of Nature’s
greatest spectacles. A display might start as a few upward shafts
of light almost imperceptible against a darkening twilight sky.
The shafts then take form, they brighten into greens
topped with reds, they join to make wide curtains, move and flicker,
they disappear then quickly return again. The silence as they change
is somehow more eerie than the lights themselves. Sometimes the display is
confined to the north, in others reds and orange cover the whole sky.
Aurorae are best seen for 2-3 hours around midnight although they
can be visible from dusk to dawn. A moonless night well away from
light pollution is ideal. They are most frequent and at their finest
at high latitudes. Aurorae are concentrated in two giant ovals around* Earth’s
magnetic poles. The northern pole is currently** in
the high Canadian Actic and Canada, Northern USA and Northern Europe
are well placed for bright displays.
The auroral ovals enlarge during high activity and displays
are then visible further south in England, Germany and mid latitude
USA. Very exceptionally, aurorae are even seen in the tropics.
Aurorae are produced by solar storms and are most frequent during
the maxima of the 11 year solar activity cycle. The last maximum
was 2000/1 and although we are now (2007) near minimum activity
there are still plenty of aurorae to see.
Solar disturbances take 2-3 days to reach Earth and aurorae are therefore to
some extent predictable. For daily oval plots and aurora predictions see links.
are only approximately centered on each magnetic pole. They are furthest
from it on Earth's midnight side.
|Locating the exact position
of the northern magnetic pole and characterising the Earth's magnetic
field was one of the subsidiary quests during the long search for a
North West Passage. The magnetic pole was then near Boothia Peninsula.
It is presently (2007) northwest of Sverdrup Island at ~83°N 115°W
. After a period of stability is is migrating quickly, ~ 40 km per
year, towards Siberia. Bad news for 2060 North American aurora observers.