Solar variation
As solar activity cyclically varying properties of the sun are called associated with the turbulence of their hot gas and ongoing changes in the magnetic field. This activity is most striking in varying degrees of frequency of sunspots and their position relative to the equator. The sunspot cycle has a mean period of 11 years, but may be over extended periods of 9-13 years. The mean number of sunspots varies from 0 to 5 in the sunspot minimum to over 100 ( around 1960 even on the 200) at the maximum ¹). For this phenomenon still irregular gas and flares (flares ), changes in the solar wind, scattered solar storms come (see geomagnetic storm ) and proton showers, and huge gas fountains of prominences.
Although sunspots have around 1000 ° lower temperature than the rest of the solar surface (5500 ° C), the sun shines during the activity maximum at a slightly higher performance than the sunspot minimum. Helped in particular by the solar flares at ( hotter areas with approximately 7000 °). The solar activity is responsible for events of space weather and directly affects satellites, but also on technical equipment on Earth. It also influences the aurora, the ionosphere and thus the propagation of radio waves on earth.
¹) is also currently (May, 2013, near a maximum), there are on some days up to 120 spots and a larger number of spot groups even relative numbers of more than 200
Measurement of solar activity
Sunspot number
The 1610 discovered sunspots are systematically observed since the 17th century and thus belong to those astronomical phenomena that are investigated longest according to modern scientific methods. A good and easily determinable measure of the solar activity is the sunspot number:
K is a correction factor for the size of the telescope used and the current visibility, g is the number of spot groups, and f is the number of individual spots.
Around 1970 began some solar observatories to measure the total area of the spots daily. This elaborate alternative method shows but almost the same activity course as the simple enumeration by relative number.
Radio intensity
Another measure of the solar activity is the radio intensity of the sun at the wavelength of 10.7 cm. This intensity is correlated with the relative number and is determined with radio astronomical methods.
Cycles
The most obvious cycle is the about 11 -year Schwabe cycle by Samuel Heinrich Schwabe. Successive maxima of the sunspot number follow each other in this time interval.
Since the solar magnetic field was found to be the cause of sunspots with the Zeeman effect, can also determine their magnetic polarity. On a solar hemisphere, the magnetic polarity of the spots from one move to the next cycle. The 11-year cycle is therefore twice as long a cycle based on the 22-year Hale cycle.
There are probably other cycles, such as the 80 - to 90 -year-old Gleißberg cycle, discovered by Wolfgang Gleißberg. There may be a connection with the years spotless minimum around the year 2008.
In terms of problems for space missions with high activity, the forecast of solar activity has received increased importance. Wolfgang Gleißberg has developed a forecasting method based on the comparison of multiple, consecutive cycles.
Radiation spectrum and origin
For several decades, notes the sun is research that solar activity is still more noticeable in other regions of the spectrum, such as the solar Radioflux is used as an activity indicator. The northern or polar lights hang along with it.
The radiant energy of the Sun comes from nuclear fusion of hydrogen into helium in the Sun's core and passes through particles ( neutrinos ), radiative transfer and convection to the outside. Through interactions results in an entire spectrum of radiation of gamma radiation over the UV to the radio waveband. There are large scale and small scale differences in temperature, gas outbursts and scattered radiation storms in the X-ray, UV and radio waves.
Hot gas clouds, flares and auroras
Strong magnetic fields in large sunspots ( Type E, Type F ) can hurl clouds of hot gas from the outer layers of the Sun into space. These gas clouds are electrically charged and therefore disrupt the Earth's magnetic field when they arrive after a few days in the earth.
Flares are sudden eruptions radiation in the outer layers that take several minutes to hours. This enhanced gamma radiation, UV and radio emission is observed. Even high-energy atomic particles (electrons, protons, helium nuclei ) can be emitted.
A geomagnetic storm remains mostly unnoticed. Severe storms can disrupt satellites, however, electrical systems, or wireless links, which happened in the past few years several times. However, while the increased radiation exposure is safe during a magnetic storm on the Earth's surface, they can be dangerous in space and on some long-haul flights.
According to the Geo Research Center Potsdam put the biggest solar storm in history on 1/2 September 1859 paralyzed the just-introduced telegraph lines and produced auroras, which were still visible in Rome and Havana. Also in the fall of 2003, auroras were seen to the south of Germany and in Austria.
Each solar observatory is used in addition to the observation of sunspots and flares and structures for the measurement of the solar corona. There are more recently special satellites that register increased gas clouds of flares long before the arrival on Earth. Also from stereo satellite of NASA hoped that new information on the physics of the sun and its anomalies.
By Andrew Ellicott Douglass has been suggested that the growth of trees may depend on the solar activity.
Long-term changes
Since the mid-20th century, the Sun is in an unusually active phase, the researchers of the Max Planck Society mean. Solar activity is thus about twice as high as the long-term average, and higher than ever in the past 1000 years. An international research team has investigated the solar activity of the past millennia. Since the end of the last glacial period the sun was therefore rarely as active as since the 1940s until today. As scientists from Germany, Finland and Switzerland in the journal Nature report (28 October 2004), one must go back over 8000 years in the history of the earth, until one finds a period in which the sun in the middle was just as active as in the past 60 years. Researchers around Sami Solanki from the Max Planck Institute ( MPI) for Solar System Research in Katlenburg -Lindau, solar activity have traced on the basis of heavy carbon atoms ( 14C). From the study of earlier periods of increased solar activity, the researchers predict that the current high level of activity of the sun is probably only a few more decades.
Current Activity
After the unusually long minimum of 2008/ 09, where the sun was spotless for months, the maximum of the current solar cycle 24 was initially predicted for the end of 2012. The increase in activity was 2011, and as expected, reaching a flat maximum in February, but fell relative sunspot number in summer 2012 again and remained until the end of the year uncharacteristically low in early 2012. The maximum forecast was therefore revised to the end of 2013.
Is unusual in the current cycle and the unequal distribution of activity centers and the large spot groups of type E and F. During 2012, the northern hemisphere of the sun was more active, are this year (2013 ) almost all of these groups in the southern hemisphere. Correlated with the solar rotation experience the highest relative numbers (approx. 130 to 160 ) since May 2013 by the middle of the month and on some spot groups are even freiäugig visible; the lowest values will be around 20
Furthermore, should every month some geomagnetic storms occur in the Earth's ionosphere to induce strong auroras after about 2 days.