Polka Dots And Sunbeams A Solar Observer’s Dream

Sunspots speckle the sun like polka dots in this photo taken early this morning by NASA’s Solar Dynamics Telescope (SDO). The largest spot (right of center) belongs to sunspot group 2055. The view is very similar to that seen through a typical amateur telescope equipped with a safe solar filter. Sunspots are regions where magnetic energy is concentrated on the sun’s surface. Credit: NASA

For a change it was wonderful to show people a heavily speckled sun at Astronomy Day festivities yesterday. If it’s clear – rare enough in itself – sunspots are usually little more than crumb-sized and look like flecks of dirt or dust through the eyepiece.

Kids and adults eager to see sunspots queue up at Jim Schaff’s dual telescopes, which showed the sun in both visible light and deep red hydrogen-alpha. Schaff, of Duluth, is at left. Credit: Bob King

But this week the past few days, the sun’s been showing off a half dozen spots as large or larger than the planet you toil upon. There are currently at least 8 numbered sunspot groups. One of them, the leader spot in group 2055, was easily seen through a #14 welder’s glass this morning.

A C4-class flare in sunspot region 2055 early yesterday evening May 10 glares in this photo made in ultraviolet light by SDO. More flares up to M-class are possible from this region in the coming days. Credit: NASA

To be visible with the naked eye (with filter), a sunspot or sunspot group has to extend some 31,000 miles (50,000 km) or about 4 times the diameter of Earth. While enormous, about 2-3% of sunspots and sunspot groups or about 100 per 11-year solar cycle can be seen by a dedicated solar observer, proving you don’t need a telescope to follow the general trend of the 11-year sunspot cycle.

The first drawing of sunspots was made by English monk John of Worcester in 1128 A.D.

The first written records of sunspots come to us from the Chinese as long ago as 800 B.C. Court astrologers in China and Korea kept tracks of spots because they believed they foretold important events. The earliest known drawing of sunspots was made almost 500 years before the invention of the telescope by English monk and chronicler John of Worchester. On Dec. 8. 1128 A.D., Brother John wrote:

“…from morning to evening, appeared something like two black circles within the disk of the Sun, the one in the upper part being bigger, the other in the lower part smaller. As shown on the drawing.”

First photo of the sun using the daguerrotype process taken by Fizeau and Foucault on April 2, 1845. Though fuzzy, you can still make out sunspot groups and the basic dark umbra-lighter penumbra structure of the spots. Credit: ESA

His sighting was followed five days later by a red aurora recorded over Korea. The two may have been related.

As long as we’re talking firsts, the first successful photograph of the sun and sunspots was made on April 2, 1845 by French physicists Louis Fizeau and Leon Foucault on daguerrotype with an exposure of 1/60 of a second. It looks pretty rough but photography only improved from there.

Nowadays, anyone with a safe solar filter for either naked eye or telescope use can see what the sun’s up to. Solar telescopes in orbit and on the ground photograph the sun almost continuously. NASA’s dual STEREO orbiting solar probes even show us what’s happening the side facing away from Earth.

A prominence eruption blasted a CME or coronal mass ejection off the northeast side of the sun very early this morning. It’s not Earth-directed. This photo was taken by the Solar and Heliospheric Observatory (SOHO) which uses a disk to block direct sunlight. Credit: NASA/ESA

We not only want to learn more about how the sun works, but we’re justifiably concerned about its storms and how they affect our planet.

15 Responses

  1. Giorgio Rizzarelli

    Thanx Bob for sharing this brief history of sunspots observation. I knew about Fizeau and Foucalt experiments on speed of light and didn’t imagine they got the first photograph of sunspots. By the way Foucault discovered the phenomenon of eddy currents – I wonder if he also discovered that it is the cause of sunspots.

    The Chinese naked eye observations are interesting as well. Did they observe the sun without a filter, I guess? If so, how could they see sunspots? Maybe at sunrise/sunset and these were unusually big sunspots?

    1. astrobob

      I’ve read they must have observed near sunset and sunrise, however, as you know well, certain clouds even at midday make perfect solar filters.

      1. Giorgio Rizzarelli

        Yes I saw sunspots using clouds as natural filter in photo. I tried that in visual but never succeeded (clouds were too irregular). Did you?

        1. astrobob

          You’re right. The clouds have to be consistent with the same texture otherwise it’s very hard to see naked eye sunspots.

          1. Giorgio Rizzarelli

            Thanx for the encouragement, I’ll try! Maybe spot 2055 is big enough, what do you think?

            Really I never succeed at sunset either (although, again, I did in photo) – Sun was too blinding to see detail so I had to wait until the very last minute, and I didn’t see details – probably too humidity (it was on sea). Did you?

          2. astrobob

            Did you mean 2055? Yes, I used a square of #14 welder’s glass and could discern the lead spot easily. It was small – I’ve seen bigger – but not too hard. I suspected one or two other smaller spots.

      2. Giorgio Rizzarelli

        Glad that the current spot 2055 can be seen without optics with filter/welder. I have variable weather these days so will try when sunny (I meant I’ll try it also unfiltered with clouds, but probably as you say the spot is not big enough).

        As for seeing sunspots at sunset in visual without filter (like antique Chinese did), I meant that I tried a few times in past, with the biggest sunspots of this cycle so far, but never succeeded (either Sun was too blinding or there was too mist). Did you?

        1. astrobob

          Whenever I see a large group I use either a welder’s glass or a Mylar filter to see if it’s visible with the naked eye. I’ve seen many groups this way over the years. Let us know if you spot 2055 – good luck!

          1. Giorgio Rizzarelli

            Sorry there’s often a bit of miscommunication when saying “seeing sunspots at naked eye”, because someone means without optics with some filter (astrosolar, welder/mylar etc), other means “all-natural” (using fog or similar as natural filter, as Norman below described). In your lastest post, do you mean you just use welder/mylar, or that you try it to see if you can then go “all-natural” without any filter/glass (like the antique did)?

          2. astrobob

            I observe naked eye sunspots almost always (about 99% of the time) through a safe solar filter like a #14 welder’s glass or optical mylar made for the purpose of viewing the sun. I rarely ever attempt to see sunspots through clouds or near sunset though I have seen them this way on occasion over the years. It’s a method that has been used by some but I don’t recommend it.

        2. Giorgio Rizzarelli

          Thanx for the detailed reply. Of course, safety comes first. If one has those fog conditions it would be worth to take a brief look, but yes these conditions are generally rare.

  2. Norman Sanker

    Hey Bob, that first photo of sunspots also shows limb darkening rather well. My best all-natural looks at sunspots have been through fog in the Bay Are where that condition was relatively common. Those peeks were occasionally comparable to a Mylar filter view. I remember coming out of my house in Richmond, CA one foggy morning, being charmed by a deer standing calmly in the middle of the road, then noticing that the sun was perfectly filtered. Gotta love Nature. –Norman

    1. astrobob

      Hi Norman,
      Nice picture in words with deer and sun. You’re right – limb darkening is easy to see in the photo.

      1. Giorgio Rizzarelli

        Thank you Norman for your report. There are not many reports on web about such natural observations. Fog was indeed used in some historical observations. I did a research on web, see a summary in my comment below.

  3. Giorgio Rizzarelli

    I did a research on web about the “naked eye sunspots” topic, and I think you’ll be interested in a summary of what I found.

    Seeing sunspots naked-eye without any artificial filter is possible (just occasionally, as you say, for safety) using as natural filter some special conditions: fog, forest fire, volcano aerosols, dust storms, certain clouds, or certain sunrise/sunsets probably together with one of the above conditions. These conditions are generally rare, but may be common in some geographical locations, as Norman below described. In his famous report John of Worcester (1128) says he had fog.
    Basically in these natural cases eye’s pupil is contracted at daylight, at 1.5-2mm (or, I add, 2-3mm, because fog light is 1 stop darker); from Rayleigh criterion, this gives the usual resolution of roughly 1arcmin of human eye. Sunspots of 1 arcmin (diameter including penumbra) appear a few times per year, in the years of maximum solar activity. So having such sunspots *and* the right conditions is not common.
    The two sunspots in the drawing of John of Worcester were probably monsters of 2-3arcmin each, but he could distinguish well the penumbra on both sides, so this is in agreement with the 1arcmin resolution.

    When using artificial filters (and still no magnifying optics) one can see at higher resolution. In fact, one has options to get a good contrast without too much glare: some use mylar or welder glass; I use Astrosolar, sometimes I add lunar filters, and I always wear photochromic eyeglasses. These options can allow the human pupil to be wider – although not fully since one is still observing details on a white disc, as if craters on the Moon. If, say, pupil doubles to 4mm, one can resolve half arcmin.
    This is indeed the limit for the filtered case, according some statistics I found on web about much data by various observers. Half arcmin sunspots are common in the years of high solar activity. I confirm that the sunspots I saw without optics, but with artificial filters, were all above 0.5arcmin (included AR2055 a few days ago). (These sunspots can be revealed also using clouds as natural filters, but with the magnification of a camera telelens).

    The visual limits above depend very much on visual acuity and observer’s experience: they are valid for a 10/10 eye and a fairly expert observer (for the beginner, the limit gets worse by a factor 2).

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