This year’s most powerful solar flare was photographed by TESIS telescopes in the southern hemisphere
of the Sun on July 5th, 2009. The flash lasted 11 minutes from 10:07 until 10:18 Moscow time,
reaching its peak at 10:13 Moscow time. At its highest point, the intensity
of solar X-rays reached level Ñ2.7 on the 5-point GOES scale.
The classification of flares is carried out by measuring the flow of solar X-rays in wavelengths ranging
from 1 to 8 angstrom. All solar flares are divided into 5 classes according to these measurements depending
on the maximum power of radiation emitted. These classes are denoted by letters of the Roman alphabet:
A, B, C, M and X. Minimal class A0.0 is registered at 10 nanowatts/square metre of X-ray flow within the Earth’s
orbit – this figure then increases tenfold between each following category. To register in the highest category,
the X-ray flow from the flare must increase to at least 100 000 nanowatts. Events of such power are unique
and are only observed during maximal solar activity. Flashes with X-ray flow of more than one million nanowatts
(up to class X17) were observed at the peak of the previous solar cycle at the end of October, 2003.
Although the observed flare is 100 times weaker in power when compared with these unique events, it is the biggest flare
(among registered flares) for a very long time.
The last time a class-C flare was registered was on December 11th, 2008,
and it was several times weaker - the X-ray flow only reached level C1.4. Events more powerful than today’s have not been
observed on the Sun for over a year; since March 25th, 2008, when a level M1.7 flare occurred.
A very slow increase in the Sun’s activity has been observed since around March, 2009. The first areas of activity,
which make up the so-called “northern belt” – a configuration, typical of the beginning of the new solar cycle – started to
form in the Sun’s northern hemisphere at the end of March after an extremely long three-year solar minimum. For two months,
all the activity of the new solar cycle was connected with areas of this belt, including the first solar flares and coronal
mass ejections of the year. Such domination of the Sun’s northern hemisphere over its southern hemisphere existed for about
two months, until the end of May, when a southern belt of activity was formed. Thus, the magnetic configuration of the
Sun became symmetrical once again following a short break.
The Sun’s southern belt of activity has existed for just over a month and is still much less developed than the northern belt.
Nevertheless, this year’s largest solar flare occurred in the southern belt. Although it usually takes a long time to
accumulate enough energy for a flare to occur, we are confident that this was not the case this time.
The fact is that
the active area, where the flare occurred, simply did not exist two days prior to the event.
It appeared on the solar disk
at midnight Moscow time on July 3rd. Therefore, either the flare energy was accumulated in magnetic fields before the area
came to the surface, or the area is developing at unusually high speed - that characteristic for maximal activity.
Observations of sunspots (the basic indicators of solar activity) support the latter conclusion. Their number in the area
is increasing extremely fast: there were no sunspots in this area on July 3rd; there were seven sunspots on July 4th;
and there were already fourteen sunspots on July 5th. The number of sunspots totalled 16 on July 6th. If there are
no changes within the next few days, the large flare, which occurred yesterday, won’t be the last this week.
Fortunately, a further increase in the Sun’s activity coincided with the beginning of the shadowless orbits of
the CORONAS-PHOTON satellite, onboard which the observatory works. The space vehicle’s orbit plane will be turned
to the Sun at an angle of approximately 90 degrees within the next two weeks. As a result, the vehicle will not enter
the Earth’s shadow while it is rotating in orbit and will be able to observe the Sun uninterruptedly.
This means that almost all of the solar events of these days will be captured by the TESIS telescopes.
Three foreign space vehicles (the Japanese HINODE satellite and two NASA STEREO vehicles) will switch over
to high observation frequency mode together at the beginning of the TESIS shadowless orbits.