Sunspots and magnetic fields – when did scientists discover the connection?

 sunspots are visible in this image of the Sun

Many sunspots are visible in this image of the Sun from the Solar Dynamics Observatory taken on 9 November 2011. Courtesy SDO/HMI

Today we are fairly knowledgeable about the Sun. We know that sunspots come and go on the Sun with a period of approximately 11 years and that spots are regions of intense magnetic fields. Sunspot groups have spots of two different polarities and the order of these polarities reverse in a cycle that is double the length of the normal 11-year cycle. These ideas are often discussed by Harry Roberts, a valued and regular contributor to this blog, for example in this recent post.

Having come across an article in the Scientific American of 10 May 1884 (pages 288-289), it is interesting to note what was known at that time and when scientists discovered the all-important magnetic fields on the Sun.

The article starts off with what is still a familiar discussion on when the maximum of the sunspot cycle would take place. In 1884 the number of spots on the Sun was near the peak of a relatively low sunspot cycle and the article quotes a number of eminent astronomers disagreeing on whether solar activity was increasing or decreasing. For the record looking at a graph of sunspot numbers indicates a peak in 1884.

The article states that little is known about the Sun though noting that there was an ‘inexplicable tie’ between auroras and magnetic disturbances and sunspots. It then says,

Whether the solar activity is the cause of the earthquakes, volcanic eruptions, cyclones, tornadoes, and the disturbances that follow in their train is a problem yet unsolved. The sun hides his secrets from mortal ken ; we do not even know his exact distance or diameter, nor can we expect in the present attainments of science to find out the cause of the spots with which the sun’s fair face has been pitted and marred for several years.

That sunspots are due to magnetic fields was discovered by American astronomer George Ellery Hale 24 years after the Scientific American article. In 1908 Hale, observing with the newly-built 60-foot (18-metre) solar tower, used a special prism to examine the polarisation of the light from sunspots. With a spectroscope the light can be broken up into its component colours and specific wavelengths or lines due to ions of particular elements can be seen. In previous work Hale knew that some of these lines are in fact close doublets, that is, instead of one spectral line due to an ion there are two that are very close in wavelength.

On 24 and 25 June 1908 he found that these doublets are polarised, that is, the radiation from the ions vibrate in specific directions. Furthermore the two components of the doublets had opposite polarisations. Hale said,

Photographs like these seemed to leave no doubt that the components of the spot doublets are circularly polarised in opposite directions. Since the only known means of transforming a single line into such a doublet is a strong magnetic field, it appeared probable that a sunspot contains such a field, and that the widening and doubling of the lines in the spot spectrum result from this cause.

Thanks to George Ellery Hale and his successors we know far more about the Sun and its spots than scientists did back in May 1884 when the Scientific American article was written. Still there is much more left to be discovered about our nearest star, so keep reading the posts on this blog for updates!

15 responses to “Sunspots and magnetic fields – when did scientists discover the connection?

  • NikolaM  perhaps the sunspots are part of the 5,000 y cycle.  I believe they and many other phenomena are part of the end cycle where the heliosphere is compressed down to about Mars.  If the Earth is outside, then we get cosmic ray exposure and expansion.  If the Earth remains inside the compressed heliosphere, the we don’t get the expansion but we do get a BLAST OUT “a hot spot” when the pressurized heliosphere disappears in a non locality event.  This is due to the neutrino core heating. 
    Fits our geologic history perfectly.  Rio Tino company just admitted to a huge gas field discovery outside of Mozambique.  As this is the compression end of the cycle, many ‘new’ oil and gas findings will happen.  

  • Already longe time I follow this kind news and an occasional I comment and real miracle is nobody is interesting in for my comment.
    I affirm the science didn’t  decipher any causes and sources of these phenomena and in this case there are no possibilities to know righ truth about it.
     I offer a collaboration .
    Milovic Nikola, dipl.ing. energ.

    • Bloggers reading this should be careful with this guy.

      He is among a bunch of people who believe in the untenable ideas “plasma cosmology” (PC) – where magnetic fields and plasma dominate the universe – exceeding gravity. They wrongly believe that these forces are scaleable, meaning that seen on the sun are also in galaxies and even the universe. Many of their ilk reject the evidence of the Big Bang and usually state that the universe in infinite (the only way they can sustain the wrong deduction of the dominance of magnetic fields.

      Certainly the sun has a relative strong magnetic fields (thousands of gauss), and the behaviour of many of the phenomena we see are the consequence these fields. However, the rest of these fields are relatively small in the galaxy (in the order of micro gauss), while intergalactic space is in the order of 0.00000000000000000001 (10^-19) gauss. There is little doubt that the universe is easily dominated by gravitation.

      Most supporters of these radical ideas have other quite unsubstantiated radical notions. I.e. Nucleosynthesis, in which star generation their energies and manufacture of heavier elements by fusion, where instead, they believe that the cause is by magnetic fields and so-called ‘pinches.’ Another is the cosmic background radiation, which mostly killed these nonsensical notions.

      Most are fanatical followers of fellows of Anthony Peratt and Hannes Alfvén, who once presented their ideas in the 1960s to the 1980s. Astrophysics and science has completely rejected most of these notions. Astronomy and astrophysics does not currently support Peratt or  Alfvén .Some of these notions are sometimes supported by the IEEE (Institute of Electrical and Electronics Engineers) members, and although scientific in nature, are not within a discipline accepted under astronomy or astrophysics. Supporters commonly claim there ideas are “peer reviewed”, which they are, but are not “peer reviewed in astrophysical disciplines. 

      There are one or two pseudoscientific ‘anti-science’ organisations who have an organised agenda to promote these radial ideas and theories.

      They continue to try and get a foothold on blog sites (like this one), and have caused such a disruption, that many sites just delete the proponents submissions. Those interested in such subjects might like to read about plasma cosmology at the wiki entry at; http://en.wikipedia.org/wiki/Plasma_cosmology

      As usual, new theories of astronomical phenomena have to build on our present knowledge and real observation. These days, for such accepted ideas to be overturned are literally nil. While Nikola might have interesting ideas, they are so ‘out there’ they are difficult to take them seriously.

      (Another idea of Nikola, for example, is “formulae for calculating Earth’s eccentricity without astronomical data.” Such ideas are both plainly silly and even dangerous.)

      Sadly for Nikola, he has not made any discovery supported by observation.

      • Appear Misters you didn’t comprehend my idea and proofs, and immediately you defend your ignorance and defect of awareness by offences. I am not such because I have MATHEMATICAL CONCLUSIVE EVIDENCE AND PROOFS for it. Here rormulae for eccentricity for Earth

        ….. e-eccentricity; exp2 =e on exp 2; ln-natural log. Verify for Earth.and help me to solve this formulae-it is complicated. Don’t believe only in instruments, make use of intuition and awarness given by God as gift.
        Please answer me with a resolve of formulae.
        And now in Serbian, because I have problem with English:

        Ono sto ste dobili i na sta ste dali nekulturan odgovor bez prethodnog sagledavanja pravog stanja mog iznosenja, ne odgovara gotovo nicem sto sam vam poslao sa zeljom da eventualno pokusamo razrijesiti neke dosadasnje nerijesene stvari u nauci. Nemojte smatrati da je danasnja nauka u pravu ako se sluzi uglavnom instrumentima a ne rasudjivanjem bez istih.
        Ja i dalje tvrdim da nauka i naucnici nisu do danas nasli ono sto uzrokuje npr sunceve pjege(sunspots).Imate pravo da je to splet kombinatorike magnetnih polja, gravitacije i sl. ali zaboravlja se da ima i nesto do cega ljudski um ne moze dosegnuti bez velikog novoa svjesnosti koja ima “linkove” sa sveukupnim recipijentom znanja u Bozijim entitetima iz kojih sve dobijamo,neko svjasnoscu a neko mjerenjima postojeceg.
        Ja imam i druge dokaze, npr. uzroke sopstvene rotacije Zemlje, koje nauka
        nije do danas objasnila jednoznacno. Odmah da vam kazem da se tu radi o
        zalihama energije nagomilane u perihelu, koja se rasporedjuje duz putanje
        nekih od konusnih presjeka osim kruga.
        Posebna je prica o tome da se moze,samo vi ne zelite da je bilo ko iznad
        vas-sto ste dokazali vasim komentarom punim uvreda,dokazati gotovo bezbroj
        cklusa i podciklusa vezano za pojave na Suncu.
        Imam jos toga samo je izgleda iluzorno tako nesto iznositi kada nije
        sazrelo vrijeme za toleranciju i postovanje i onih koji nemaju sredstava za
        ekserimentisanje, vec da pariraju svojom svjesnoscu.
        Best regards,
        Milovic Nikola, dipl.ing energ.

        • “Don’t believe only in instruments, make use of intuition and awarness given by God as gift.”

          That isn’t a definition of science that I was ever taught!

        • What has ln[(1+e)/(1-e)]exp[(1-eexp2)/2e]=1 to do with the sunspot cycle or the behaviour of the solar magnetic field?
          The Earth’s orbital eccentricity ‘e’ is not constant, but varies over 100,000 years or more. It changes are caused by the combined perturbations from all the planets and bodies in the Solar System. Eccentricity of the Earth’s orbit varies between roughly 0.003 and 0.06. At present it is about 0.02. 

          Climate change sceptics are claiming have in recent years attempt to discount humans influence and replace it with explaining the changes on astronomical influences such as eccentricity of the Earth’s orbit, mean distance from the Earth from the sun or ‘a’, Earth’s axial tilt / obliquity to the ecliptic , or the 11 year sunspot cycle (or other longer periodicities.) 

          I assume you are referring to ideas like the Milankovitch theory – which also has the properties of adiabatic invariance. Alternatively you probably consider that solar radiation is variable irradiance and so-called solar insolation; just to support ‘personal’ science. Sorry, I don’t buy it.  

          Many do claim some ultimate proof, but mostly it is based on little or no evidence. Language issues aside, I don’t think what you ask is relevant to this story nor is based on accepted science. 

          I will NOT be solving your equation. It is not relevant here.

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