Solar Viewing

CJ Thomposon
McDonald Observatory Davis Mountains
N 30 68.084', W 103 01.502';
Elevation 6602.3’ (at HET)
Satellite Image

Content:
On the final morning of our field experience we returned to McDonald Observatory for something quite unique. We participated in a solar observation. Marc Wetzel, one of our presenters, used a computer interface to point smaller telescopes at the sun. Once our closest star was lined up, he opened the larger scope. By changing the filter on the telescope, Marc was able to make different components of the sun visible. The first things we saw were some sunspots. These dark spots, which move slowly across the face of the sun, appear dark only, as Marc explained, because they are relatively cooler than the surrounding material.

To demonstrate how this works, Marc set up a light bulb, hooked up to a dimmer switch, on the overhead projector. With the projector on and the light bulb at its highest setting, the filament in the bulb could clearly be seen glowing against the lighted background of the overhead. Marc turned the dimmer switch down until it appeared the bulb was no longer illuminated. The filament now appeared dark. However, when the overhead was switched off the filament could be seen to still be glowing. It only appeared dark against the background of the illuminated overhead projector because it was cooler.
This little animation tries to mimic a demonstration you can use in a classroom to show why sunspots appear dark. Leave the overhead turned on. Notice that, with the dimmer switch set on the highest setting, the filament can be seen glowing against the background of the overhead projector. Slide the dimmer switch to the left just until the filament turns dark. It probably looks like the bulb is now off. Use the toggle switch to turn off the overhead. You should see that the filament of the bulb is still glowing. It appeared dark only against the illuminated background of the overhead when it was on. In the same way sunspots, though they are very hot, are still cooler than the surrounding material and so appear dark.
Next we saw some prominences and solar flares. A prominence is an arc, or series of arcs, that stretch from one sunspot to another, in effect, bridging the pair. A solar flare is a stream of solar material that shoots out from the sun. Both are related to magnetic fields generated on the sun. Marc used a cylindrical (cow) magnet suspended in the center of a container of oil and iron filing to demonstrate the lines of a magnetic field and show how they are mimicked by the curves of a prominence. Reflection:
I found the entire experience both fascinating and informative. In addition, everything was relevant to state standards, especially TEKS 5.11D (“describe the characteristics of the sun.”) Most helpful were the resources given to us. One invaluable resource is the website spaceweather.com. Among other items, this website offers a constantly updated image of the sun. Their archives allow you to view images from days in the past, affording an opportunity for students to see patterns of change.
This animation displays images of the sun over a two-week period in mid February, 2005. You can start and stop the animation and also step forward and backward through the images to see how sunspots move across the sun.
I found out that viewing the sun with students is a simple matter. While you never want to look directly at the sun, projecting its image can be rather simple. A sheet of white paper held a few centimeters from the eyepiece of a telescope or binoculars will act as a screen for viewing the image of the sun. One just has to be careful about using a filter since the concentrated sunlight could melt components. I found a simple and easily transported solar viewer at the website for Orion telescopes (telescope.com) which would make a wonderful addition to any classroom. Of course the least expensive alternative is a pinhole viewer, plans for which can be found at exploratorium.edu. No matter what you choose, solar viewing makes a great part of any space curriculum since the sun is usually the only heavenly body visible during school hours. Happy viewing!

Tuesday, June 6, 2006