A solar cycle is one period during which the activity of the Sun varies by reproducing the same phenomena as for the period of the same duration preceding.

Seen Ground, the influence of the Sun varies mainly according to a period day laborer and annual. In the absolute, the solar activity is regulated by a one 11,2 years average period cycle of a maximum at the following but the duration can vary between 8 and 15 years. The amplitude of maximum can vary the simple one with triple. The 11 years cycle was given for the first time by the Astronome German amateur Heinrich Schwabe towards 1843. In 1849, the Swiss astronomer Johann Rudolf Wolf (1816 - 1893) establishes a method of calculating of the solar activity based on the number of spots. The cycles of Schwabe are numbered starting from the maximum of 1761 (see table). In 2003, the cycle 23 is on the decline, the cycle 24 will begin in 2012.

In connection with the 11 years cycle, exists a 22 years cycle which relates to the solar magnetic field. Indeed, the polarities of this last are reversed with each new 11 years cycle.
A 179 years cycle can be also highlighted. A theory (K.D. Wood) gives for reason of this cycle solar the “tides” caused by the Planet S of the Solar system, mainly Venus, Ground, Mars and Jupiter; the Period of revolution of Mercury being too weak with respect to the duration of the 11 years cycle. Wolf also noticed a cycle of variation of maximum one 90 years period. During the maximum businesss year, one notes an increase:

• of the number of sunspots and the solar starts
• of the corpuscular radiation
• of the electromagnetic radiation

Sunspots

Two thousand years ago, the Greek and Chinese astronomers spoke in their writings about dark spots on the sun whose form and site changaient. In April 1612, Galileo made their observations using one of the first telescopes. Thereafter, the observatory of Zurich continued the observation of it. They appear in photosphere like a dark zone (shade) surrounded by a clearer area (half-light), are colder than ambient photosphere (4 500 K against approximately 5.800 K for the Photosphère), and are due to a local increase in the magnetic field. Their greater dimension can reach several tens of thousands of km.

The spots often appear groups some, and are often accompanied by other spots of opposite magnetic polarity (bipolar group of spots). At the beginning of the solar cycle, the spots appear preferably with high latitudes in the two hemispheres (towards 40); moreover, the first spots of a group are in general of the same polarity. Throughout the cycle, the spots will approach the equator until the beginning of the following cycle; at this time there, the polarity of the spots of front changes.

The observation of the sunspots is easy and makes it possible to note the rotation of the sun on itself in 27 days. One however never should directly look at the sun without adapted glasses. One can observe the spots by projecting the image of the sun on a sheet of paper using a simple pair of binoculars.

The Wolf number or Sunspot Number

The following formula makes it possible to estimate the solar activity R according to the number ( T ) of spots, number ( G ) of groups of spots and of a coefficient K correcting the result according to the observation aids (observer, instrument…). $R=k\; (t+10g)$ The Wolf number maximum of cycle 19 reached 190 while the cycle 14 did not exceed 70. In spite of its inaccuracy the Wolf number to the interest to exist since 250 years while the scientific observation with modern means has only some cycles in its databases.

The measurement of solar radioelectric flow

The Radioastronomie was born with the Radar, in 1942 during the Second world war. The radio waves emitted by the Sun come from the Chromosphère, where the matter is entirely ionized (plasma) and of the crown. The Fréquence of the emitted wave depends on , the density of ion/m³.

The solar disturbances (eruption, starts) vary the spectrum radio transmissions.

The measurement of the amplitude of the solar Rayonnement on 2800 MHz (in W/Hz m ²) gives an index of solar activity more reliable than the Wolf number. Measurements are also taken on other frequencies (245 MHz, 410 MHz,… 15,4 GHz)

The study of the solar activity makes it possible to include/understand the phenomena of propagation waves and to lay down possible disturbances of the radioelectric communications on Earth.

Consequences

The variations of the solar activity result in fluctuations of the propagation of the waves radio. The frequency band the most touched covers the waves known as decametric or Short waves which is propagated with long distance thanks to the Ionosphère. During the magnetic storms, the very strong ionization of the high layers of the atmosphere can even disturb to stop the communications with the satellite S with the serious consequences that have can imagine it for the Télécommunications, navigation, the geographical positioning…

Calculation of the calendar solar cycle

Attention: this concept does not have a relationship to the physics and the magnetic cycles of the Sun, nor with the calculation of the number of the cycles of Schwabe (top of the page).

The solar cycle is the name given to a parameter of the Calendrier used in the ecclesiastical comput.

In the ecclesiastical comput, the solar cycle is the one year old row in the 28 years cycle of a scale of time starting arbitrarily in year 20 of the Christian era. In the Calendar Julien, the days of the week are found at the same dates at the end of 28 years and in particular Sundays, days formerly devoted to the Sun.

There exists a Everlasting calendar founded on the solar, valid cycle in the calendar Julien and playing the same part as the everlasting calendar founded on the Sunday letter.

The knowledge of the solar cycle is equivalent to that of the Sunday Lettre Julienne.

Method of calculating by taking 2006 for example:

• To add 8 to the year (2006+8=2014);
• To take the remainder in division by 28 (2014/28≈71,9 truncated with 71. However 71×28=1988 instead of 2014, it thus remains 26);
• To add 1 (26+1 = 27)

The solar cycle of 2006 is worth 27.

See too

Internal bond

• Climate changes
• solar Meteorology

External bond

• Solar activities

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