Sunspot
Sunspots are dark patches on the solar surface ( photosphere ) that are cooler and therefore emit less visible light than the rest of the surface. Their number and size is the simplest measure of the solar activity. The frequency of sunspots is subject to a periodicity of an average of eleven years, which is called the sunspot cycle. Cause of the stains and the outbreaks occurring in their vicinity are magnetic.
- 4.1 relative sunspot number
- 4.2 10.7 - cm radio flux index
- 5.1 Forest Meier classification 5.1.1 Stages of development
- 5.1.2 Type of Group E
- 5.1.3 Type of Group F
Formation
As the Sun consists of fluctuating gas, also moves its surface is not uniform: Your equatorial regions rotate approximately in a 25 - day cycle, while those of the near polar latitudes 30 days or more need for a round. This results in the course of a cycle (see below) to bias the inner - first bipolar - magnetic field. It caused local field sheets that break through the photosphere and share the matter out into the corona; the resulting cooling of the surface is visible as a spot. Where the field lines are perpendicular, it is darkest ( Umbra ), where they extend obliquely to the surface, it is less dark ( penumbra ).
Since the arcs each having an input and exit point, sunspots occur in pairs. The leading end spot (English: leading spot) is the solar equator closer than the past (English: trailing spot); this deviation decreases with increasing distance from the Sun's poles. The polarity of the leading spot corresponding to that of the respective sun hemisphere, for the past, the opposite is true.
Later in the cycle, the spots become more frequent and larger ( group formation). Recently they accumulate at the equator, where they largely cancel each other out; the rest of the magnetized gas fields is carried to the poles: The total magnetic field of the sun is again uniform (bipolar), but with reversed polarity.
The exact properties of the underlying, so-called solar dynamos are not yet been fully explained.
Sunspots are usually lined by faculae or Plages: hot regions that emit high-energy radiation. If there is a "short circuit" of the field sheets, the magnetic field collapses abruptly and the adjacent plasma is released; the result is a coronal mass ejection.
Properties
The average surface temperature of the sun is about 5500 ° C ( "effective temperature" 5770 Kelvin, radiation temperature 6050 K). At this temperature, the maximum of the emitted energy is mostly in the range of visible light, as the sun approximated as a Planckian " black body " radiates. The core region of a sunspot, called the umbra ( " umbra " ), has only about 4000 ° C, the edge area - or even yard - the penumbra ( " penumbra " ) 5000-5500 ° C. In these somewhat lower temperatures, the radiation intensity in the visible light decreases already significantly. Umbra and penumbra therefore appear much darker when observed through a solar filter or in the eyepiece.
Cause of the slowdown are strong magnetic fields that interfere with the convection. Therefore, the sunspots in visible light show the most active regions on the Sun. If the number of sunspots is a greater chance that two adjacent but oppositely polarized magnetic field lines reconnect ( reconnection ) and the released energy is emitted into the room. A visible variant are the flares. If there is an outbreak of radiation toward Earth, this can lead to significant disturbances in Earth's magnetic field, and even affect the operation of satellites and electrical systems on Earth. In addition, such a radiation burst increases the probability of auroras in temperate latitudes.
With a gauge of the Solar and Heliospheric Observatory, the sound velocity could be measured both in the vicinity of sunspots as well as up to 24,000 km depth. The cause of the sometimes considerable differences has not yet been clarified.
In years with reduced spot number also the solar radiation is reduced by about 1 ‰. The years 1645-1715, the so-called Maunder Minimum, during which no sunspots were observed, coincident with the Little Ice Age. However, it is not clear whether the small changes in solar activity are sufficient to explain climate change.
With the variation of solar activity also changed the Earth's ionosphere. This has implications for the radio transmission in the shortwave range. ( See also: amateur radio )
Sunspots usually occur in groups, but begin as small single spots. On the basis of sunspots can observe the rotation of the Sun as they move along on the surface. At the equator the sun rotates with 25.03 days ( synodic 27.9 days ) is about 20 % faster than near the poles.
Sunspot from December 13, 2006, Ø ≈ 20,000 km, tinted grayscale image from Hinode, 480-640 nm
Magnetic field around a sunspot
Simulation of the magnetic field lines on the sun
Cycles
The sunspot cycle refers to the periodicity in the frequency of sunspots. He describes an average period of 11 years, which is referred to by Samuel Heinrich Schwabe as Schwabe cycle. The minimum spot no spots are often for months to see the sunspot maximum but hundreds. Within this cycle, the spot areas change their helio- graphic latitude and the magnetic polarity, so that they are actually a 22- year cycle followed ( Hale cycle after George Ellery Hale).
One cycle
The 11 annual sunspot cycle is not exactly regular. Although the average score is 11.04 years, also occur in cycles 9-14 years. Also, the average varied over the centuries - the solar cycles in the 20th century, for example, were 10.2 years on average, shorter than those of the past centuries. The course of the further minima Maunderminimums and sets a variation of the total intensity of the sun close to a time scale of several 100 years. From the 10Be distribution in the Greenland ice one concludes that more than 20 Sonnenminima within the last 10,000 years.
The flow of the cycle itself is not constant. So said the Swiss astronomer Max Meier forest that the transition from minimum to maximum of solar activity takes place more rapidly, the higher will be the maximum. In contrast to the steep rise but the number of sunspots increases in such cycles only slowly.
In cycles with a low maximum number of sunspots, the phase of the rise and the fall is approximately the same length.
The beginning and end of a cycle,
The beginning of a new cycle is initiated from in the past from the low point of the cycle curve. Due to improved measurement technique, it is now possible to determine the magnetic field polarity of sunspots. A new cycle begins when the polarity of related swapped spots on the solar surface. The resolution of the picture on the right is too small to read the changes can. However, the reversal of the polarity between the neighboring stages can be clearly seen.
The cycles were given by Rudolf Wolf, a consecutive numbering, starting in 1749 (see story). Currently we are in the 24th cycle.
During the decay tail of the 23rd through to 24th cycle were both sunspots of the old polarity and in reverse polarity to observe new in March 2008. The actual minimum and the unique beginning of the 24th cycle could not be distinguished itself in October 2008. The quiet sun makes a late weak maximum in 2012 and an even weaker expect to 2023. Maybe a new Maunder Minimum begins.
* Forecast on May 2009
As mentioned above, the two spots of a bipolar group have a different magnetic orientation, as well as the leading- spots on the northern hemisphere opposite magnetic orientation of which they have the southern hemisphere. Within a sunspot cycle, but does not change the polarity of the leading spots. This will change with the next sunspot cycle, so that a complete cycle comprises 22 years ( Hale cycle).
In the 19th century and until about 1970 it was assumed that there is still an approximately 80 - annual period ( Gleißberg cycle, according to Wolfgang Gleißberg ) could indicate that in low values of the relative number R 1800-1840 and (less clearly ) 1890 -1920 expressed. Recent research have left of this hypothesis again or explain the fluctuations caused by a kind of super - convection. Other hypotheses are contradicted not only by the 80 - year cycle, but still by an additional 400 - year cycle.
Width effect
At the beginning of sunspot cycle, the first spots form in about 30 ° - 40 ° helio graphic width north and south of the solar equator. Over the subsequent years, the formation regions move further and further towards the equator. Halfway through the cycle, the solar activity is at its highest and the sunspots appear in about 15 ° of latitude. The number and area expansion is now the largest. At the end of the cycle, scattered spots form in about ends ± 5 ° of latitude, and the cycle repeats. At the same time forming in high latitudes, the first patch of the next cycle.
Plotting the distribution of the degrees of latitude and the extent of the spots in a diagram of the time ( Spörers Act), the result is the butterfly diagram called - like the open wings of a butterfly.
Active longitudes and the flip- flop cycle
Since the beginning of the 20th century they were looking for excellent longitudes where sunspots appear preferred ( active longitudes), but the search for a long time without success - the longitudes found varied depending on processing method both in number and in their situation, they also were not stable over long periods. However, at the beginning of the 21st century, the situation seems to be changing: Usoskin and Berdyugina investigated the approach " migratory longitudes " and found two 180 ° offset active longitudes which are subject to differential rotation and not changed over the investigated period of 120 years. After the results of the first publications were questioned as a possible "artifacts" of the used evaluation and filtering technique that results could now be demonstrated to the raw data without further filtering.
The two active longitudes are not running: The activity changes within a solar rotation from one to another, the average period of 3.8 years here in the northern hemisphere and 3.65 in the southern hemisphere - about a third of the Schwabe cycle. This cycle was discovered already in 1998 in the activity of stars, also called flip-flop cycle.
Quantification of sunspots
Relative sunspot number
The frequency of sunspots has long been the so-called relative number (also called Wolf'sche relative number, defined by Rudolf Wolf) detected. It is one of the single spots ( figure f) and added to ten times the number of groups ( g ), where individual spots (type A and I ) are considered "group". This simple measure of solar activity
Has proven itself for over 100 years as good as the expensive area measurement of sunspots (maximum per mille of the sun surface ).
By simple calculation to R can be estimated to far back into the past - more specifically from 1610, the year of the invention of the telescope. The headquarters of many observatories daily reported these measures are, by the end of 1979, the Swiss Federal Observatory in Zurich since the data at the Royal Observatory of Belgium are collected. The resident organization called S.I.D.C. (Solar Influences Data Analysis Center). But there are a number of other observers networks that collect and exchange data with each other.
In a year minimum R is on average 5 to 20 (de facto 0-3 small spots ), at the time of the maximum increase the monthly average to 60 to 200 ( average about 5 to 10 larger spot groups). However, since the visibility of spots increases with the size of the telescope used, Zurich formula has been developed which relates to a " standard telescope". This sometimes strange relative numbers come about (eg, in a single spot R * = 9 instead of observed R = 11), - what but the value of the measure does not detract.
Even with a small telescope of 5-10 cm aperture can be solar activity and cycle, rotation, butterfly effect and other well observed (see also solar observation ). Of course, you may never see an unshielded telescope at the sun - which can cause eye damage! As a professional tool for safe observation of special solar filters or special lenses ( Herschel wedge, H -alpha filter) are used. The easiest way is to project the image of the sun on white paper by the eyepiece screwed out by a few millimeters and the paper is held a few inches behind it ( eyepiece ) is. The north may be better simply because the image travels through the Earth's rotation due west.
10.7 - cm radio flux index
The sunspot number correlates very strongly with the radio wave radiation from the Sun at 10.7 cm wavelength. The radiation intensity is referred to as radio flux index F10.7. The radiation density is measured in W / m / Hz, sometimes expressed in Jansky, but mostly in solar flux units ( sfu ):
The solar flux is suitable for measurement of solar activity better than the sunspot number, as it depends on the subjective, manual counting of sunspots. It can be in the sunspot number and vice versa converted.
Classification
Meier forest classification
From the Swiss astronomer Max Forest Meier (PhD 1935 ) the idea of a classification of different types and sizes of sunspots comes in a scheme which reproduces the temporal development: from small single spot ( type A, see picture) to huge shaded areas (type e and type F) and the subsequent regression.
Small stains (A) develop from so-called pores (larger cells of the granulation), but often disappear after a few hours. Existence it a little longer, they are magnetically bipolar ( type B or C ), and sometimes can be D or further develop E / F and persist for several weeks as up to 250,000 km long sunspot group. Mostly, however, the regression of B- or C- spots goes directly to the types H or J.
Stages of development
The local amplification of the magnetic field hindered - as mentioned above - the heat transport of some convection cells. The darker grain size of these granules ( about 1000 ° C cooler ) is becoming a single spot ( type A). Some of them disappear within a few days, others evolve into a bipolar group of two (B). From them larger groups (A to D Type C) develop with penumbra sporadically reach the stage I / F with up to over a hundred spots. The regression of these to 200,000 km large spot groups (see title picture) to small double - and single spots (H, I) are within a few weeks or months.
According to this classification of forest Max Meier ( 1940 ) so not all of the small patches of type A / B to larger spot groups of the type C and higher, but at most to small pores with Penumbra (stage H or I). Only if they develop one of the largest types D, E or F, they can be double dark spots with penumbra in the regression. Such pairs are always polarized magnetically different, and on the other hemisphere opposite. This is an indication of large, slow currents inside the sun that causes even the 11 -year cycle.
Type of Group E
A sunspot group of type E is the second largest stage of development of bipolar spot groups. You can only at high solar activity - that is, in many sunspots - occur several times a month.
Type E has a number of individual spots ( 20-100 ) and as Type D, F, and G distinct penumbra. There, the temperature of the solar gas ( an average of almost 6000 ° C) is just over 5000 ° C, compared to 4000 ° C in the darkest parts of the umbra. A typical e- group has dimensions of 10 Earth radii; the earth itself would disappear in some single spot.
Type of Group F
A sunspot group of type F is the largest area, but not very common stage of development of bipolar spot groups. An example can be seen on the photo above.
According to the classification of forest Max Meier, not all small sunspot groups of type A or B evolve to larger spot groups of the type C to E. With a sufficiently high solar activity, ie, in many magnetic disturbances and sun spots, produced type F but often of the type E and sets it ahead.
Type F has the largest number of individual spots ( up to about 200) and the maximum area of so-called penumbra, the penumbra. There, the normal temperature of the solar gas is reduced by only about 500 to 1000 ° C, compared to 2000 ° C in the darkest parts of the umbra.
After about 2-10 weeks, the group is of the type G or H until disappearance as a single spot ( type I) back.
Further classifications
In the period 1875-1997 the Royal Greenwich Observatory carried out extensive observations of the sun. Sunspots were divided with 10 categories in individual spots, couples, groups and their combinations.
History
Some sunspots are so big that you can see them with the naked eye as in a sunset. Record of it there for over 2000 years. Observations of Anaxagoras (about 467 BC) can not be clearly assigned to. Theophrastus von Eresus ( 4 / 3 rd century BC) speaks in his " weather signs " clearly of a spot on the sun. Come from China, records from the years 165 and 28 BC
An observation made in 1128 by John of Worcester went unheeded, as the former world view could only imagine a " flawless " sun. Any stains therefore had to be objects between Earth and the Sun, such as undiscovered planets, moons and clouds.
In different eras but also appeared performances that saw dark holes, floating slag or cooler places in the sunspots.
After the invention of the telescope, the systematic observation of sunspots began. The oldest private recording dates from this period of December 8, 1610 by Thomas Harriot. In March 1611 Johann Fabricius published the first time on sunspots.
Long-term studies have been conducted independent of Galileo Galilei and Christoph Scheiner. Galileo wrote in 1613 in his lettere solarized of his reaching back into the 1611 observations. Scheiner discovered from the tower of Holy Cross Church in Ingolstadt on the morning of March 21, 1611 together with his pupil Johann Baptist Cysat sunspots. Galileo took early today believes that the spots are structures of the solar surface. This brought him next to his advocacy of the heliocentric world view, a first method Inquisition in 1615 a.
The observation of sunspots was then carried out sporadically because of Maunderminimums ( 1645-1715 ). During these 70 years the sun had a period of low sunspot activity. Around that time the lighter areas of the solar flares were discovered.
Already in the 18th century, the Danish astronomer Christian Pedersen Horrebow expressed the suspicion that some activity phenomena in terms of their frequency point to a certain periodicity. In Goschen ribbon Astrophysics of WF Wislicenus 1899 ( first edition) and 1909 ( 3rd edition by Hans Ludendorff revised) is the following purpose:
" 1775 spoke Horrebow from the assumption that the stains show a certain periodicity with respect to the frequency of their publication. This assumption was confirmed by the investigations Schwabe in the 19th century. "
Christian Pedersen Horrebow (1718-1776) was, like his father Peder Nielsen Horrebow (1679-1764) director of the observatory in Copenhagen, which was located until 1861 in the Round Tower.
However, the credit for the discovery of the cyclical nature of sunspot activity fell to the Anhalt pharmacist and amateur astronomer Samuel Heinrich Schwabe of Dessau. Due to his everyday observations in the course of 17 years ( 1828-1845 ) he also noted that the frequency of sunspots in an approximately 10 - year trend fluctuates periodically. Schwabe submitted the dossier and its conclusions the former director of the Swiss Federal Observatory in Zurich, Rudolf Wolf, which she confirmed.
Based on the thousands of other sun indications and designations of sunspots from the period from the 17th to the 19th century, Wolf began the periodicity of sunspots calculated back over the year 1826 up to Galileo. Wolf reconstructed by the statistical behavior of the solar activity from 1749 on, called the Zurich time series.
Wolf numbered sunspot cycles and chose as a starting point the 0th cycle with its maximum in 1749. Previous cycles were given negative numbers.
News
Through the images of the STEREO satellites, the researchers hope new knowledge about sun anomalies. The 3D information should help to better understand the physics of the sun and allow better predictions about the influence of solar activity on the Earth.
In addition, two other satellites play an important role in the observation of the sun: the come in the years since 2010 the SOHO and SDO.