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Courtesy of the Jet Propulsion Laboratory
Naked eye observations of the Sun will result in blindness. The improper use of telescopes or binoculars will cause blindness much faster. Now, having said that, there are safe and easy ways to safely observe the Sun. Do not hesitate to use them.
The Sun and some of its behaviors are well know to youngsters. They know the difference between night and day and the realize that the Sun is up longer during the summer than in the winter. But few, if any, of your students have ever directly observed the surface of the Sun. They have no reason to expect that the Sun is spinning or that it has blemishes which evolve over time.
If these facts are covered in a textbook students are forced to accept these statements on faith alone. That is not a particularly compelling way to learn. It is possible for students to discover important details about the Sun themselves.
Incorrect observation of the Sun causes blindness because of the tremendous amount of visible and invisible light coming off of its surface. Sunglasses and other inappropriate filters may block visible light but can not cut out enough ultraviolet and infrared light, causing the eye's retina to burn out.
Looking through thick clouds or with UV-blocking sunglasses is just as dangerous. Fortunately, two things prevent major problems. The first is that it is painful to look at the Sun. Eyes tear up and you have to look away. The second is that few youngsters bring sunglasses to class.
A projected image of the Sun is, however, perfectly safe to observe. Binoculars, with the front of one ocular covered, can be used to project a sharp image of the Sun on to a white piece of paper. The binoculars are attached on a tripod, with a mount or securely with tape. Place a piece of cardboard, at least 20 by 25 centimeters (8 by 10 inches), with one hole the same size as the front of one ocular at the front of the binoculars. Fasten it securely with tape. It will cast a shadow on the paper.
Aim the binoculars by tilting them up and down and back and forth until the Sun shines through. Never look through the binoculars when they are pointing anywhere near the Sun! Sharpen the image of the Sun on the paper by using the binocular's focusing knob or lever. The size of the image can be altered by moving the paper closer or farther from the binoculars.
Sunspots are appropriately named. They appear as spots on the disk of the Sun. A sunspot will have a very dark central region known as the umbra. It is often surrounded by a less dark halo known as the penumbra. Think about the root and prefix of this word for a good language lesson. The umbra is dark because it is cooler (around 3,500°C/6,300°F) than the surrounding sunscape (around 5,500°C/10,000°F).
Spots change over a period of several days. Penciling in the detailed appearance and location of sun-spots on a fresh piece of paper over several days can give a clear illustration of this.
They also move across the Sun as the Sun spins on its axis. Because the Sun is fluid it does not spin as a rigid body. A spot near the equator will take about 25 days to complete one rotation. A spot near a pole, if there were ever one there, will take over a month to make the trip. Collections of sketches over a period of several years will also reveal the 11 year cycle of sunspots. Over that period the numbers of spots goes from a maximum to a minimum and back.
As with any experiment, follow good scientific procedures. Keep appropriate records by being sure that all papers have the date, time and appropriate viewing conditions written in the margins or on the back of the drawings. Read more about sunspots and their interesting behavior.
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