Black Holes to Blackboards: The Sun is a Mass of Incandescent Gas

Jeffrey F. Lockwood
Sahuaro High School

Not only can the Sun turn night to day, it can transform obscure 1950s jingles into 1990s alternative-rock hits.

The baritone voice starts the song and rumbles on:

The sun is a mass of incandescent gas,
A gigantic nuclear furnace,
Where hydrogen is built into helium
At a temperature of millions of degrees.

Not the usual context for the Sun in popular music; no tequila sunrise, no sunwheel dance, no sunshine of my life. Don McCarthy, who plays this song for his undergraduates in Astronomy 101 at the University of Arizona, says his students think it soooo corny. Yet he catches them singing and humming the words for months afterward.

Ditties that lodge in the mind are just one of many ways for students to learn about the (second) most accessible object in astronomy: our Sun. Studying the Sun can tie together subjects across the curriculum. After all, it is the mother of life on Earth. Almost all species on our planet, with the exception of a few fascinating but obscure life forms that reside deep under water or underground, depend on sunlight.

The Sun itself is a cauldron of incessant change. Sunspots and prominences--the tongues of hot plasma which shoot off the Sun's surface and arch gracefully back, following the invisible tethers of magnetic field lines--are just two examples of solar volatility. The Sun's fickleness has been linked to dynamic shifts in Earth's environmental and biological histories. Indeed, because solar activity can knock out power lines and interfere with communications, the National Oceanic and Atmospheric Administration issues daily solar weather reports.

Sunspots are especially fascinating to investigate. For over two centuries, astronomers have relied on sunspot counts to monitor solar activity. The number of spots oscillates on an 11-year cycle, and more spots usually mean more flares and other activity. Your students can count sunspots by projecting a solar image from binoculars or a small telescope onto a piece of tag board, or by using other devices such as a Learning Technologies' "Sunspotter." The black dots will be easy to see. Several books, such as Peter Taylor and Nancy Hendrickson's recent Beginner's Guide to the Sun, describe the procedures in detail.

Students' sunspot numbers can vary quite a bit because of their interpretation and experience, the quality of the image, and the appearance or disappearance of spots in the course of the day. The daily official number, computed from a network of observatories worldwide, is on the web (http://web.ngdc.noaa.gov/stp/SOLAR/solintro.html). Past years' sunspot numbers can be downloaded from this site and plotted along with your students' data. The patterns are quite revealing. Other web sites let students in climatically challenged cities catch an occasional glimpse of the Sun (http://umbra.nascom.nasa.gov/images/latest.html).

The daily and seasonal motions of the Sun, as seen from Earth, offer other opportunities for student inquiry. For a simple observation, have your students do a sunrise or sunset watch. (Most prefer sunset, I don't know why.) Students should face the Sun and draw in the buildings, trees, and power lines on their horizon. Each day, ask them to mark the position of sunset on their horizon, labeling the position with the time and date. Over one or two months, they will notice dramatic motion. One variation: At the end of their observation period, have your students draw daily sunset positions on separate sheets of paper to create a flip-book movie.

Plotting the Sun's daily motion is a classic exercise described in the Project STAR and Universe at Your Fingertips activity manuals. Students first predict the path of the Sun across the celestial sphere, then go outdoors and plot the actual path. Do this lab at least twice during the school year, preferably near a solstice or equinox. Middle-school groups can build sundials to make their measurements. The "Solar Motion Demonstrator" is a good follow-up [see The Universe in the Classroom, winter/spring 1995, pp. 6, 10]. High-school students can use the demonstrator or a celestial sphere to estimate the number of hours of daylight and the height of the Sun above the horizon on any day of the year.

Other quantitative exercises abound in both of the activity manuals. In "Finding the Size of the Sun and the Moon," students gauge the diameter of the Sun and Moon by using a simple pinhole camera. In another activity, they use simple equipment (200-watt light bulb, paraffin block, aluminum foil, ruler) to measure the luminosity of the Sun in terms of light bulbs. And the old standby, a scale model of the Sun and Earth, benefits all groups of students.

Studying the Sun can provoke discussions of climatic and environmental conundrums such as the evolution of glaciers, ice ages, mass extinctions, and the possibility of life around stars like ours. Students can develop a respect for an object that was revered as a god by ancient cultures and whose mysteries have yet to be plumbed by present-day scientists.

Yo ho, it's hot, the sun is not
A place where we could live
But here on Earth there'd be no life
Without the light it gives.

JEFFREY F. LOCKWOOD is a high-school and college astronomy and physics teacher at Sahuaro High School and Pima Community College in Tucson, Ariz. His email address is iplockwood@aol.com.

Note: An article on the birth, life, and death of the Sun, "Biography of a Star," appears in the latest issue of The Universe in the Classroom, third quarter 1997.