SHARON SHANKS | The Cosmos There's more to sun than meets the eye

Let's do a drawing exercise today.
Use your crayons (borrow some from your kids or grandkids if you don't have them handy) and draw a picture of the sun. Hmmm, not bad. Most of you drew a yellow circle with lines coming from it. Now, to finish your masterpiece, splatter mud all over it -- and you've produced a good representation of the real sun.
The sun isn't muddy, of course, but it certainly looks like someone's taken a fistful of mud and splattered its surface. The "muddy areas" are sunspots, and the sun currently had a bumper crop of these dark irritations on its surface.
This year marks the peak of the 11-year solar cycle, more familiarly known as the sunspot cycle. Like a rider on an endless roller coaster track, the sun is at the top of its cycle of activity. After it passes the peak, the sun's activity will gradually wind down over a period of about five years, and it will spend a year or two of quiet time in solar minimum. Its activity will then pick up and grow for about five years before reaching another peak period around 2012.
Upside down: Astronomers believe the sun is at its solar maximum point now because our star's magnetic poles recently flipped. Like Earth, the sun has magnetic north and south poles. At the time of solar maximum, the sun's magnetic field flips. What had been north from our point of view is now pointing through the southern hemisphere.
The sun's magnetic poles will stay that way until the next peak of sunspot maximum.
Earth's magnetic field also flips, but not on a regular cycle and at much longer intervals. Reversals happen 5,000 to 50 million years apart; the last reversal took place about 750,000 years ago.
If you want to add sunspots to your drawing, be sure to add a monster of a spot for one of the sun's "eyes." The largest sunspot in 10 years was spotted late last week and may still be visible on the disk of the sun. It is easily visible to the unaided eye. (But remember to shield those eyes! The same safety measures you'd use for viewing a solar eclipse can be used to observe sunspots, including the use of special eclipse glasses made of aluminized mylar.)
Enormous: The spot covers an area on the sun equivalent to the surface area of 13 Earths. The total number of sunspots has been hovering around 300 for several days.
Sunspots look dark because they are cooler than the rest of the surface of the sun -- only about 3,300 degrees C (6,000 degrees F). The photosphere, the visible surface, averages about 5,500 degrees C (about 10,000 F), while the chromosphere, the inner atmosphere, registers at 10,000 degrees C (18,000 degrees F).
To get to the really hot spot, you'd have to travel to the core of the sun, where temperatures reach 15 million degrees C (17 million degrees F).
The sun's corona is also very hot -- about 2 million degrees C (3.6 million degrees F). The corona extends millions of miles into space around the sun.
Sunspots are caused by variations of the sun's magnetism, which don't allow hotter gases to reach the surface. They normally appear in pairs with opposite polarities; imagine an ordinary bar magnet resting on the surface, with sunspots at each end.
Sun storm: This year's biggest sunspot to date is small compared to the monster of a sunspot in March 1989 that triggered a massive geomagnetic storm. This is the storm that knocked out electric power for 6 million people in Canada and the United States for nine hours.
Astronomers measure the size of sunspots by comparing them against the visible area of the sun. Their unit of measure is a millionth -- a one-millionth sunspot has a surface area equal to .000001 times the area of the sun that's facing the Earth. As a comparison, the surface area of Earth is 169 millionths of the visible solar disk.
Using this scale, this week's big sunspot measured 2,200 millionths. The sunspot that disrupted the power grid in 1989 was more than 3,500 millionths.
Neither match the size of the whopper of a sunspot called the Great Sunspot of 1948 (it deserves the capitals). It measured about 6,100 millionths.
While we still have our crayons out, let's draw in some more lines to represent the energy we receive from the sun. The yellow lines can stand for visible light, the form of energy we're the most familiar with.
Rainbow of waves: Use red crayons to make more lines to represent energy in the infrared part of the electromagnetic spectrum, and use purple to represent energy in the ultraviolet. Although the sun emits radiation across the electromagnet spectrum, from long lazy radio waves to short energetic gamma rays, most of the radiation from the photosphere is in the areas of infrared, ultraviolet, and visible light.
We'll have to add additional details to our sun to have a complete picture. Use your yellow crayons to draw short, fat, wavy lines. These are prominences, dense clouds of material suspended above the surface by loops of magnetic field. You can make some of the prominences look like fat U's.
All over the surface of the sun you need to draw short lines to represent spicules, vertical jets of gas only about 10,000 km (6,200 miles) high, and macrospicules, which can reach 40,000 km (25,000 miles) high.
Now use white and add a small white circle to represent a solar flare, an explosion in the sun that takes place when stored energy in magnetic fields near sunspots is suddenly released.
That about completes our picture of the sun, at least the elementary version. Fore more about the sun, sunspots, space weather, and how the sun functions, the best spot on the Web is at www.spaceweather.com.