TO THE CASUAL OBSERVER, THE sun is immutable. It shines constantly with a bright white light that changes to reds and yellows only when scattered or absorbed by particles and vapors in our planet's variable atmosphere. A closer look reveals, however, that the sun is far more dynamic than the earth. Cataclysmic storms periodically erupt on the sun's surface-storms that could easily envelop several earth-size planets.

Regions of intense activity on the sun's surface are somewhat cooler than the area that surrounds them. For this reason, active regions appear dark when viewed against the hotter and therefore more brilliant solar disk. These active, dark regions are known as sunspots. Now is an excellent time to observe them, for it is only a few months past the peak of one of the most turbulent periods of solar activity ever recorded [see Figure 2].

Some spots cover such a large fraction of the solar disk that they can be seen without magnification. Indeed, more than 1,700 years before the invention of the telescope, Chinese astronomers observed sunspots without the assistance of a magnifying device. Although I have long been aware of such ancient reports, not until March, 1989, did I personally look at sunspots without a special telescope. In separate accounts on the same day, two acquaintances informed me that they had seen a large spot on the sun while driving to work. The sun was low on the horizon, and they were able to view it safely through a layer of fog.

By the time I received these reports, the fog had long since vanished. I therefore drove to a nearby welding store and purchased a filter plate that is designed for an arc-welder's helmet. Within a few minutes the store's staff and I were outside looking at a large group of sunspots through plates of welder's glass.

Serious sun watchers will recall this unusual group of some 50 spots by its formal name, region 5395. Thanks to widespread media coverage, the rest of us will remember region 5395 as the cluster of spots that gave rise to a solar flare, which in turn caused a spectacular, luminous display in the night sky over most of the Northern Hemisphere. This display, known as an aurora borealis, appeared as far south as the Florida Keys and Cancun, Mexico.

When an aurora appears that far south, you can be sure that someone, somewhere, wishes it had not. That is because the increased solar activity that generates the aurora can have many deleterious effects on and near the earth. The orbits of satellites, particularly those in low orbit, can be altered; radio communications can be disrupted; and electric power grids can be subjected to power swings and even blackouts.

Region 5395 caused more than its fair share of such mischief, a compilation of which was prepared by Joe H. Allen of the World Data Center A for Solar-Terrestrial Physics in Boulder, Colo. Power fades or outages occurred in New Mexico and New York. Six million residents of Quebec Province went without electricity for nine hours or more on March 13. These blackouts cost power utilities a total of 187 million kilowatt-hours.

Sunspot region 5395 was also responsible for many problems with broadcast systems. The earth's upper atmosphere usually refracts radio signals, but it absorbs them when it is bombarded by intense solar radiation. The opposite is true for higher-frequency signals: they propagate far beyond their usual range. During the lifetime of region 5395, these effects provided many interesting experiences for both amateur and professional operators of radio-communications systems. The effects also explain why some homeowners in California complained that their radio-controlled garage doors were mysteriously opening and closing on their own. That phenomenon was apparently caused by a nearby Navy transmitter. The station had shifted operation to a new frequency, because its standard frequencies were rendered useless by the effects of the sun on the ionosphere.

Despite all the trouble that sunspots cause, they can be a pleasure to watch. And you can gain a better appreciation of the dynamic nature of the sun by observing it daily for a month or so. You will find this project informative and considerably more convenient than those conducted by the professional and amateur astronomers who study stars other than the sun. Whereas these investigators often stay up all night in pursuit of their quarry, you will be able to observe the sun anytime during the day. You can even watch through haze or smog or from any room that has a window facing the sun.

The simplest and fastest way to look for large spots is to look at the sun directly through a suitable filter, as I first did during the appearance of region 5395. It is absolutely essential that the filter attenuate the sunlight to the proper degree. Welder's filters are rated according to the amount of light they transmit. The darkest available filter has a rating of 14. It transmits 2.7 times less light than a number 13 filter, which transmits 2.7 times less light than a number 12 filter and so on. Only a number 14 filter provides enough protection for your eyes against direct sunlight.

Welder's filters are available in at least two sizes: five by 10.8 centimeters and 11.4 by 13.3 centimeters. The small filter provides a pocket-size solar observatory that you can carry with you to check for large spots during traffic jams, lunch breaks and hikes. The large filter, which will fit in a coat pocket or purse, provides somewhat more comfortable viewing since it shades most of the face. I paid $1.95 for a small filter and $4.40 for a large one. Since some welding stores do not stock filters with a shade darker than number 12, it is a good idea to call first.

Some welding stores stock plastic filters coated with a metallic film. Although these filters have the same attenuation factor as glass filters marked with the equivalent shade number, a scratch in the metallic coating can allow the transmission of damaging rays. For this reason, a glass filter is a better choice.

No matter what kind of welder's filter you purchase, under no circumstances should you attempt to use such a filter in conjunction with a telescope or binoculars! These instruments gather more than enough light to damage your eyes, even if they are protected by a filter. Furthermore, a glass absorption filter placed between your eye and a telescope's eyepiece can be shattered by the intense heat caused by the magnified image of the solar disk.

The sun appears yellow or yellowish-green through a glass welder's filter and gold through a plastic filter. The glass filter can be tilted to increase its attenuation, a helpful adjustment when attempting to discern small sunspots. If your first glance discloses no obvious spots, look at the edge of the sun and then the entire disk. If visible spots are present, one or more may pop into view when you shift your view back toward the full disk. Indeed, that is precisely what happened when I stepped outside in the course of typing this paragraph. A first look revealed a dear solar disk. After shifting my field of view around several times, suddenly two large spots appeared on opposite sides of the sun's equator.

A large welder's filter will let you try a viewing-enhancement trick I serendipitously discovered. While watching the sun through the filter, tilt the top side of the filter away from your forehead until a blue patch of sky is reflected into your eyes [Figure 3]. A blue field will now be superposed over and around the solar disk. Because the filter is tilted, the sun will appear dimmer. The reflected skylight wR1 contract the pupils of your eyes, thereby making the sun appear dimmer still. In my experience this technique greatly enhances the visibility of sunspots.

This rather primitive observation method can be more rewarding than it might at first seem. Since we are still near the peak of the current 11-year sunspot cycle, you might have the opportunity to watch the progress of a major sunspot group. In late August of 1989, for example, my pocket-size observatory revealed a very large spot on the sun's east limb. Three days later the spot had grown into two giant spots connected to each other-a fact that confused even professional astronomers. At first the two spots were assigned separate names, regions 5669 and 5671. When astronomers analyzed the magnetic structure of these two regions, however, they found the spots were indeed a single massive sunspot group. So regions 5669 and 5671 were combined and designated region 5669.

This highly unusual sunspot group was the source of several major bursts of radio waves, light waves and X-rays. I followed region 5669 for nearly two weeks until it rotated over the sun's west limb. One morning a few minutes after sunrise, I had a rare opportunity to see region 5669 through a thick haze and ordinary sunglasses.

Region 5669 was so large and its geometry so unusual that I wanted to examine its structure in greater detail. I therefore used a pair of binoculars to project a clear image of the solar disk onto a sheet of paper. The easiest way to implement this method is to mount the binoculars on a camera tripod. Some camera stores sell an adapter that will let you mount many kinds of binoculars on a tripod.

Under no circumstances should you look through the binoculars while attempting to aim them at the sun! Nor should you sight along the side or top of the binoculars. Instead, place a lens cap over one of the two apertures, and point the binoculars in the approximate direction of the sun. Then adjust their position while watching their shadow. When the shadow has the smallest profile, the binoculars are almost properly aligned. At that point, move them slightly until a faint image of the solar disk appears in the shadow. Align the binoculars until the disk is nearly centered in the shadow. When it is, place a cardboard light shield over the front of the open lens in order to shade the image of the solar disk and make it much brighter. Then place a white sheet or card 20 to 30 centimeters away from the binoculars, and carefully focus the binoculars for the sharpest image.

The projection method of viewing sunspots can be implemented with most binoculars and telescopes and is by far the safest method. It is important, however, to realize that curious children might attempt to look through the eyepiece of an instrument pointed at the sun. You must therefore supervise children (and adults who should know better) who are near any optical instrument that has been aimed at the sun. For even the briefest glimpse at the solar disk through a small telescope can cause a permanent and significant loss of vision. You should also be aware that binoculars or telescopes fitted with a reticle can be damaged if they are used to project solar images. The intense, focused light from the sun can burn cross hairs and melt plastic reticles.

If you have a small telescope, you can easily assemble a permanent solar projection observatory. Two years ago Vicki Rae Mims, my teenage daughter, did just that. Vicki constructed her system from scrap lumber, a clipboard, a cardboard shade and a small 10-power telescope. A finder telescope from a larger telescope will work fine. You may also purchase a small telescope from a supply company, such as Edmund Scientific Company (101 E. Gloucester Pike, Barrington, NJ 08007). Vicki's observatory is illustrated in Figure 1. For your own solar observatory, you might want to increase the distance between the telescope and the clipboard in order to enlarge the projected solar disk.

To operate your observatory, you should lean the telescope end of the device against a fence or on one of the rungs of a stepladder. Remove the cardboard shade from the telescope and move the ground end of the observatory toward or away from the support until the telescope's shadow is centered on a sheet of paper held fast by the clipboard. The telescope will now be pointed approximately at the sun. You can then make fine adjustments until the solar disk is centered on the sheet of paper. Then replace the cardboard shade to brighten the image of the sun.

With this simple projection system, you can track the movement of spots across the solar disk. You will first need to center the disk on a sheet of paper held by the clipboard. Mark several points around the perimeter of the projected image, and then draw a circle through the points. You may wish to add a system of coordinates or a grid pattern so you can better specify the location of interesting spots. Provide places for the date, time and comments. Make this sheet of paper your master chart, and copy it.

To record the movement of sunspots accurately, you should make your observations at the same time each day. This schedule guarantees the sun will be oriented in the same way each time you observe it. If your daily schedule will not permit this, align the system, and watch for a few minutes as the sun's image drifts across the chart. If necessary, rotate the clipboard or the entire observatory so that a sunspot moves along or parallel to a previously drawn grid line.

Eventually you should find the approximate north pole on the solar disk. At local apparent noon in the Northern Hemisphere, celestial north is at the top of the sun. The actual north pole will be within 26 degrees of celestial north. If a scene viewed through your telescope's eyepiece is inverted, the top of the projected image of the sun at noon is north. If not, the top of the projected image is south.

For four months Vicki made almost daily observations of sunspots using this system. She measured the rotation of the sun by tracking several spots and groups completely across the solar disk. Vicki observed that some spots moved across the solar disk faster than others, a difference that occurs because the gases at the solar equator rotate more rapidly than the gases toward the poles.

While observing projected sunspots, periodically move the paper back and forth. This technique will help remove the effects of the paper's surface texture and bring out details you might have missed. Although the images you see can be saved with the help of a camera or video recorder, many amateurs prefer to mark the sunspots with a pencil, as Vicki did. Doing so lets you indicate small spots that might be missed by film or a video camera. But, unless you have an automatically guided telescope, you have to work fast. If there are many spots, you will have to realign the telescope periodically to make sure the solar disk stays superposed over the outline on the paper.

Serious watchers may prefer to monitor the sun with an astronomical telescope that allows either projection or direct viewing. Direct-viewing instruments are usually equipped with metallic-film aperture (not eyepiece) filters. An instrument of reasonable quality will reveal that the central dark portion, or umbra, of some sunspots is surrounded by a lighter region known as the penumbra. You may also be able to classify sunspots and sunspot groups according to their size and appearance. One classification system is described in Figure 4. You may wish to consult the references that follow for additional information and safety precautions.

Whether or not you elect to pursue a regular program of sunspot observations, you will find many other ways to keep up with the latest developments on the sun. A brief summary of current solar conditions and related geophysical activity is broadcast at 18 minutes past each hour by radio station WWV The message is updated every three hours. You can receive WWV on a shortwave receiver at frequencies of 2.5, 5, 10, 15 and 20 MHz. Because WWV continually broadcasts precision-time measurements, you can set your watch while waiting for the latest solar-activity update. If you do not have access to a shortwave receiver, the WWV message is also available by telephone. The number is (303) 497-3235.

The Space Environment Services Center in Boulder operates an experimental Public Bulletin Board System (PBBS), which will send current information and forecasts about solar activity to a personal computer equipped with a modem. You can access the PBBS by dialing (303) 497-5000. (To access the system, you will need to know that the protocol is an eight-bit data word with one stop bit and no parity at either 300 or 1,200 baud.)

Another excellent way to keep up with solar events is to subscribe to the Preliminary Report and Forecast of Solar-Geophysical Activity. This weekly publication gives highlights of solar and geomagnetic activity and forecasts activity for the next 27 days. The official sunspot number is reported, and a complete list of X-ray and optical flares is given. Of particular interest are the graphs comparing the current solar cycle with previous cycles. If you cannot find the report at a nearby technical library, you can purchase a subscription from the Space Environment Services Center, NOAA R/E/SE2, 325 Broadway, Boulder, CO 80303-3328. The price for U.S. subscribers is $37 per year.

Bibliography

A COMPLETE MANUAL OF AMATEUR ASTRONOMY. P. Clay Sherrod with Thomas L. Koed. Prentice Hall, 1981.

OBSERVATIONAL ASTRONOMY FOR AMATEURS. J. B. Sidgwick. Dover Publications, Inc., 1981.

THE SUN. Iain Nicolson. Rand McNally and Co., 1982.

WATCHING THE PREMIER STAR. Patrick S. Mcintosh and Harold Leinbach in Sky & Telescope, Vol. 76, No. 5, pages 468-471; November, 1988.

The Society for Amateur Scientists (SAS) is a nonprofit research and educational organization dedicated to helping people enrich their lives by following their passion to take part in scientific adventures of all kinds.