Introduction: Sunspots are some of the most notable features of the Sun. Use a telescope to track the changes in position and shape of sunspots over time. This activity requires adult supervision.McDonald Observator

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University of Texas at Austin

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22 S ta r D at e / U n i v e r S o  t e a c h e r  G U i D eThe Sun is a huge sphere of gas. The visible layer of the Sun, which we view as the surface, is the photosphere. Its temperature is about 6,200 degrees Celsius (10,340 degrees Fahrenheit). Above the surface are the chromosphere and corona. Sunspots are some of the most noticeable features of the Sun.Materials• Telescope (with finder covered)• Piece of  white cardboard mounted on a tripodPreParationThe easiest way to position the telescope (since the finder is covered and you don’t want to “sight” along the side) is to move the telescope until its shadow is smallest. If  your telescope doesn’t have a special motor, the image will slowly track across the cardboard as Earth rotates. You may use binoculars, although too much sunlight can cause heat to build up inside the binoculars and dam-age them. For binoculars, the standard size (7x35) works satisfactorily.exPeriMentDraw a circle around the edge of  the Sun on some paper placed over the cardboard. Now quickly sketch the positions and sizes of  all the vis-ible sunspots. Write the time and date on the edge of  the paper. Repeat your observations over several days or weeks. (If  you trace the images on very thin paper, you can later overlap them to see changes.) Be careful to include the fine detail that surrounds some sunspots. An alternative is to download images from web sites each day to use for this activity or to com-pare to your own data.analysis1. Can you identify any sunspots or sunspot groups? Did they change shape, size, or position over time?2. If  you move the cardboard screen farther away, what happens to the image?3. (Advanced) The diameter of  the Sun is about 1.4 million km (864,000 miles). Measure the diameter of  your image and estimate the physical size of  your largest sunspot. Earth is 12,700 km (7,900 miles). Compare your largest sunspot with the size of  Earth. Find the size of  the sunspot with a proportion equation:4. Why are sunspots dark?SunspotsReveRsed PolaRityWhen a character in TV science fiction faces a tough technical prob-lem, one solution always seems to work: reverse the polarity.That may not fix problems in real life, but for the scientists who study the Sun, reversing the polarity is a big event. It signals that the Sun has started a new 11-year cycle of magnetic activ-ity.A new cycle began in January, when telescopes on the ground and in orbit measured a small sunspot — a rela-tively cool, dark magnetic “storm” on the surface of the Sun. The observations showed that the polarity of the sunspot was reversed from that of the sunspot before it.As the Sun spins on its axis, different layers of hot gas spin at different rates. That generates a powerful magnetic field around the Sun.Over a period of several years, the lines of magnetic force get twisted and tangled. That produces many more sunspots. The lines can also cross each other, creating “short circuits” — pow-erful explosions of energy and particles. These outbursts can disrupt communica-tions and electrical systems on Earth.At the end of a cycle, the Sun’s mag-netic field flips over: magnetic north becomes magnetic south, and vice versa.The Sun has been quiet for the last few years. But the start of a new cycle means that it’ll get busier in the years ahead. The new cycle should peak around 2012, and end around 2019 — when scientists will once again be waiting for the Sun to reverse polarity. 1,390,473 km diameter of  Sun’s image in mmsunspot diameter in kmsunspot image in mm=This is the transcript of  a StarDate radio episode that aired June 13, 2008. Script by Damond Benningfield, ©2008.S ta r D at e / U n i v e r S o  t e a c h e r  G U i D e   23answers1. Sunspots change size and shape over a period of  days. The Sun rotates on its axis in about 25 days (its equator rotates faster than its poles). Observations taken over a period of  several days should show this.2. As you move the cardboard screen back, the image becomes fainter and larger.3. Large sunspots can equal Earth in diameter.4. Do the following demonstration to illustrate that sunspots appear dark since they are cooler than the photosphere (they are about 4,500 degrees C/7,100 degrees F). Attach a dimmer switch or rheostat to a clear incan-descent light bulb. Place the bulb on its side on an overhead projector. With the projector on, focus the bulb so that the filament appears as a sharp silhouette on the screen. Turn up the power until the filament glows against the screen, then turn the power down until the filament is just barely dark against the background. Turn off  the projector and the bulb will seem to glow dimly by itself. Sunspots are only “dark” with respect to the hotter, brighter back-ground of  the photosphere.national science education standards•	Content	Standard	in	9-12	Science	as	 Inquiry	 (Abilities	 necessary	 to	do	scientific	inquiry,	Understand-ing	about	scientific	inquiry)Spanning more than 13 times the total area of Earth’s surface, this large group of sunspots photographed in 2001 coincided with the peak of the 11-year solar cycle (see sunspot number chart below). Inset: Close-up view of a typical sunspot.1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000DAT E0100200300SUNSPOT NUMBERNOAO/NSF!safety warningDo not look directly at the Sun, especially with a telescope. You can PERMANENTLY DAMAGE YOUR EYES! When working with students, it’s best to cover the finder telescope completely so that they cannot look through it. Never trust filters that go into the eyepiece or that cover the objective.Sunspots Subjects: Our Solar System  Grade Levels: 6 - 12  Sunspots are some of the most notable features of the Sun. Use a telescope to track the changes in position and shape of sunspots over time. This activity requires adult supervision.  Texas Essential Knowledge and Skills Science: §112.18-20 grade 6-8 (b)-4(A) use appropriate tools to collect, record, and analyze information, including journals/notebooks, beakers, Petri dishes, meter sticks, graduated cylinders, hot plates, test tubes, triple beam balances, microscopes, thermometers, calculators, computers, timing devices, and other equipment as needed to teach the curriculum. §112.18-grade 6 (b)-11(A) describe the physical properties, locations, and movements of the Sun, planets, Galilean moons, meteors, asteroids, and comets. Astronomy, grade 9-12: §112.33(c)-10(A) identify the approximate mass, size, motion, temperature, structure, and composition of the Sun §112.33(c)-10(C) describe the eleven-year solar cycle and the significance of sunspot §112.33(c)-10(D) analyze solar magnetic storm activity, including coronal mass ejections, prominences, flares, and sunspots. 

Sunspots

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Sunspots

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