This is also a term used to refer to the discoloration of the skin, due to UV exposure. They are often spots on the skin where there is excessive pigmantation. They span from just slight areas of discoloration, to skin cancer.

A sun spot is an area of cooler plasma on the sun's photosphere. This cooler area is roughly 3000-4800 kelvins. These sunspots are caused by magnetic field lines that pop up through the sun's photosphere. Normally the magnetic field lines on the sun are in the convection zone, but if they twist enough they can kind of poke up through the photosphere. This is much like twisting a rubber band until it pokes up in the middle. Sunspots usually occur in pairs. One in the beginning of the magnetic loop and the other is the end. Plasma from the sun gets trapped in these loops causing many different kinds of solar phenomenon.

Sunspots are regions of strong magnetic field on the sun's photosphere. They appear as dark areas on the sun's surface (the umbra) surrounded by a less dark penumbra. They may persist for days or even months.

The frequency with which they occur varies in an eleven year cycle. At the beginning of the cycle they appear at latitudes of +/- 30o and subsequently progress towards the solar equator.

However, this cycle is not always followed and between 1645 and 1720 it stopped altogether (a period known as the Maunder minimum). During this time there was a mini ice age in northern Europe.

This type of irregularity in the sunspot cycle may explained by chaos theory.

sun-stools = S = super source quench

sunspots n.

1. Notional cause of an odd error. "Why did the program suddenly turn the screen blue?" "Sunspots, I guess." 2. Also the cause of bit rot -- from the myth that sunspots will increase cosmic rays, which can flip single bits in memory. See also phase of the moon.

--The Jargon File version 4.3.1, ed. ESR, autonoded by rescdsk.

Before the write-up proper, here is a sub-node

How to burn a hole in your retina

1. Point an astronomical telescope (or other optical instrument) towards the sun 2. Look through the eyepiece. 3. There is no step 3

There is no pain, and no smell, but it is the easiest and surest way of making yourself partially blind.

Don't do it. Ever.

Damage to the retina caused by focussing the sun's rays on it is permanent. The damage cannot be repaired by time, surgery, transplants or spectacles.

Sun Spots—the intro

Basically, sunspots are small, dark regions on the "surface" of the sun. They appear dark compared with the surrounding areas, only because they are a little less hot (around 3700K) than the surrounding stuff (around 5700K).

There is a lot more to it than that, however. What, for example, does the "surface" of the sun mean? How are sunspots linked to magnetic fields? Why does the number of sun spots vary over an 11- (or 22-)year cycle?

To answer these questions, we need to learn a bit more about what the sun is and how it works.

Briefly, the sun is a star. It is a pretty average star, sitting somewhere near the middle of the main sequence, with average temperatures, half-way through its average lifetime of 9000 million years, average mass and average size (diameter 1.4 million km). It works by converting mass to energy in nuclear reactions. The conversion process releases lots of energy, and the outward pressure of this energy prevents the star from collapsing under its own weight.

Although nuclear fusion and gravity govern the overall size and energy balance of the sun, magnetism plays a very important role in its detailed behaviour.

Inside the sun, there are lots of different layers, which exist at different temperatures and different pressures. As we move radially out from the centre of sun, the pressures and temperatures fall, until we reach part of the star we can see: the photosphere.

Literally,the sphere which gives off light, the photosphere is at a temperature of around 6000 Kelvin. That is hot enough to melt most materials, but it is not mind-bogglingly hot. We can quite easily achieve that temperature here on earth. Inside the sun things really are mind-bogglingly hot, while the corona is outside the photosphere and reaches around 1 million K, which is also hot enough to boggle the mind. The bit of the sun we see when we look up at the noonday sky is (almost) the coolest part of the sun.

To answer my first question, the photosphere is taken to be the 'surface' of the sun.

The sun is a ball of very hot fluid stuff hanging together in a dynamic equilibrium between gravity and radiation pressure. It so happens that this ball of stuff spins around its axis. But the rate of spin at the equator is faster than the rate of spin at the poles. At the equator, the star stuff completes a revolution once every 10 earth days or so, but at the poles, the rotation rate is slower—perhaps once every 20 earth days. The sun is constantly twisting itself up like a rubber band

One of the effects of this is to tangle up the magnetic field lines within the sun. Although the sun is a large body with very powerful magnetic fields, this variable rotation rate makes the field lines even more complex and tangled. Another aspect of the sun is that it is made from plasma. This a very good electrical conductor. Thus, with physical motion, strong magnetic fields and electrically conducting fluids, we have all the elements required to generate very strong physical forces and violent motion (Think motors and generators).

Sunspots are themselves centres of high magnetic field density. This is cause-and-effect. If the magnetic field lines were nice and parallel, the local temperature in the photosphere would be similarly well-ordered. It takes energy to tangle up the field lines, and where the lines are especially mixed up, the energy is sucked from the local environment, giving rise to a local cooling in the photosphere at exactly the points where the field is most powerful.

So a sunspot is a slightly cooler area of the photosphere, but the reason for the cooling is that energy has been taken away from the local environment to generate very strong, complex magnetic fields. Darker (cooler) sunspots mean more energy for magnetic fields, and potentially more violent motion.

Most sunspots are around 1500km in diameter, though they can be bigger than the earth (13000km). As noted above, the sunspot temperature is typically around 2000 degrees (K) cooler than the surrounding photosphere. They last a few days, or perhaps a couple of weeks, flowing with the material of the photosphere as it rotates about the solar axis

Just as nature abhors a vacuum, it really dislikes tangled magnetic fields. They take up energy and are unstable So when the magnetic fields get too twisted up, the energy balances allow the lines to suddenly untangle themselves, with a huge release of energy. The resulting forces are capable of throwing large lumps of solar matter out into space. We can see the result of these re-alignments of the solar magnetic field in flares and prominences coming off the sun.

The amounts of energy involved in these coronal mass ejections are huge. Ten orders of magnitude greater than a terrestrial nuclear bomb.

One last question remains: Why the 22-year sunspot cycle?

You have probably guessed by now that the sunspot cycle is linked to magnetic activity. Scientists are still working on the exact mechanism for this cycle, but it is known that the polarity of the sun's magnetic field flips every 11 years, at the solar maximum. One flip (north-to-south) is half a full cycle, so the full north-south-north cycle takes 22 years. Astronomers know that a new half-cycle has begun only when they see the magnetic field flip over .

Sunspot numbers and locations have been recorded in Zurich, Switzerland since 1749. Astronomers can plot this data, showing number of spots, and their latitude on the sun against time. The resulting pattern (called a butterfly diagram) shows that at the start of the cycle, the spots (and hence areas of high magnetic field activity) are concentrated around 30 degrees from the equator (north and south). As the cycle progresses, the two populations move toward the equator. Soon after the two populations meet, the whole solar magnetic field flips over, and a new half-cycle begins, with the magnetic activity once more focussed on higher latitudes.

A note on observing sunspots

First read the micronode at the top of this write-up. Looking at the sun through any optical instrument is dangerous in the extreme.

Galileo Galilei was the first European to observe sunspots. In 1610, he turned his telescope on the sun, and used it to project a large image onto a white screen. This revealed for the first time, blemishes in the perfection of the solar disk.

The best way to observe sun spots is indirectly. Mount the telescope on a tripod, or preferably an equatorial mount, and point the objective toward the sun. It is probably best to leave a lens cap on until you are ready to start observing.

Arrange a large white sheet of paper or card (the projection screen) about 500mm away from the eyepiece, and then, making sure the telescope is pointed directly at the sun, remove the lens cap. The sun's image should form a large circle, perhaps 100mm in diameter on the projection screen, Move the screen back and forward, and adjust the focus to get a good image. Because of the rotation of the earth, the sun will quite quickly move out of the field of view, so you may have to keep adjusting your telescope position. .

Sunspot is the real-but-tongue-in-cheek name of a small hamlet in the Sacramento Mountains of southeastern New Mexico. It was given this name because it is the home of the National Solar Observatory and the bedroom community housing its scientists. Sunspot is located about fifteen miles south of Cloudcroft, just off of SR 6563, and lies within the Lincoln National Forest.

The origins of Sunspot date to 1947, when the High Altitude Observatory and the United States Air Force began site selection for a national observatory dedicated to studying the Sun. In April of the following year, the Air Force contracted out to Harvard University (co-founders of HAO) to build the observatory at Sacramento Peak, in the Sacramento Mountains east of Alamogordo. Construction of observatory buildings, telescopes, and housing units began immediately, though the early living and working conditions weren't so good. Roads in the area were so primitive that during the winter of 1948, warm clothes had to be air-dropped to people working on-site! But eventually, the project expanded to include a few dozen housing units for permanent staff, apartments for visiting astronomers, and paved roads. The observatory itself is located on Sacramento Peak, but the community was given the name Sunspot with the establishment of a post office in 1953. It is mostly in honor of the work done there, but is also a reference to the crystal clear daytime skies that Sunspot is graced with.

There are several dozen scientists and their families living in Sunspot, all affiliated with the Solar Observatory as technical support or research staff. In 1997, Sunspot opened a Visitor Center, where the general public may tour the observatory grounds and view exhibits on general astronomy, the work done at Sunspot, and the National Forest Service. However, as a bedroom community it has few amenities that larger communities might have, and grocery shopping and whatnot has to be done in the nearby communities of Cloudcroft or Timberon. Sunspot is also at high-altitude -- over 9200 feet (almost 2800 meters) above sea level -- so it takes awhile to get used to working and sleeping there.

The nearest neighbor to Sunspot is the Apache Point Observatory (APO), about a twenty minute walk from Sunspot. The Sacramento Peak Observatory conducts observations during the day, and Apache Point takes over at night. APO has its own housing facilities, but when they have more people than beds on-site, scientific visitors are frequently given accomodation in Sunspot apartments. Some of the Apache Point telescope operators live in Sunspot as well. Beyond that, Sunspot is a very tiny island in the wilderness. However, despite the isolation, Sunspot is in the midst of some very beautiful country, situated as it is within the Lincoln National Forest. Autumn is especially beautiful up there, with its mixture of birch, aspen, and maple trees. And of course, you have the view -- when the air is clear, you can see the entire Tularosa basin, including Alamogordo and White Sands National Monument in the basin, and the Organ and San Andres Mountains about fifty miles to the west.

As a final note, the name "Sunspot" isn't the only awful pun related to the site. The road passing through the housing area is called Coronal Loop. And the highway to the observatory, SR 6563, comes from the wavelength (in angstroms) of the Balmer-α emission line observed in the solar chromosphere.

Beyond firsthand knowledge, I also obtained some historical information from

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