Northern Lights or Aurora Borealis
The latest forecast is:
So what causes the activity?
To answer this, we start with the sun whose energy production
is far from even and fluctuates on an 11 year cycle. Maximum production
coincides with high sunspot activity when processes on the sun's surface throw
particles far out in space. These particles are called the solar wind and cause
the northern lights. The sun's surface temperature is approximately
6,000C, much cooler than the interior which is several million degrees. In the
sun's atmosphere or corona, the temperature rises again to several million
degrees. At such temperatures, collisions between gas particles can be so
violent that atoms disintegrate into electrons and nuclei. What was once
hydrogen becomes a gas of free electrons and protons called plasma. This plasma
escapes from the sun's corona through a hole in the sun's magnetic field. As
they escape, they are thrown out by the rotation of the sun in an ever widening
After a few days travel through space, the plasma
reaches earth's magnetic field, gets compressed on the daylight side of the
earth, and stretches into a tail on the nightside, which
stretches out into a long cylinder. Its diameter is equivalent to 15-30 times
the earth's diameter, and its length up to 500 times.
When the northern lights break out the solar wind strengthens and the magnetic tail becomes unstable. Charged particles
dive inwards towards the center of the tail and cause it to increase in length
and to taper. Most of the northern lights we see come as the electrons accelerate into the ionosphere.
How Often Can They Be Seen ?
Well it all depends on where you are:
Within the so called auroral zone, the aurora can be seen every clear winter night.
There are other regular variations:
The aurora is most frequent and intense from 22.00 to midnight, magnetic time.
- Brilliant auroras often occur at 27-day intervals as active areas on the sun's surface face earth
during its 27-day rotation cycle.
- Northern lights are more frequent in late autumn and early spring. October, February and March are
the best months for auroral observations in say northern Norway.
- Northern lights activity corresponds closely to sunspot activity, which follows an 11-year cycle, but
there seems to be a one-year delay between sunspot maximum and maximum auroral occurrence.
- Northern lights activity is 20-30% less during solar minimum than at solar maximum.
Sunspots are the dark part of the sun's surface that is cooler than the surrounding area. It turns out it is cooler because of a strong magnetic field there that inhibits the transport of heat via convective motion in the sun. The magnetic field is formed below the sun's surface, and extends out into the sun's corona. As well as being a darker area on the sun, a sunspot is an area that temporarily has a concentrated magnetic field. This magnetic force inhibits the convective motion, which ordinarily brings hot matter up from the interior of the sun, so the area of the sunspot is cooler than the surrounding plasma and gas. But sunspots are still actually very hot. Instead of being about 5700 degrees kelvin like the rest of the photosphere, the temperature of a sunspot is more like 4000 degrees kelvin.
The latest picture of the sun and any sunspots can be seen below:
On average Northern lights can be seen during the solar maximum at:
Almost every dark and clear night
Five to ten times a month
Roughly three nights a month
Roughly once a month
Two to four times a year
Mexico and Mediterranean countries
Once or twice a decade
South of the Mediterranean countries
Once or twice a century
Once in two hundred years