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The Sun Help (page 3)

By — McGraw-Hill Professional
Updated on Sep 16, 2011

Spots And Storms

If you’ve never looked at the Sun through an appropriately filtered telescope, don’t pass up the chance. Be sure that you use the proper type of filter (one that fits over the telescope’s objective lens, not in the eyepiece or the star diagonal), and use it according to the manufacturer’s instructions. Chances are good that you will see at least one dark spot on that bright disk.

Before the time of Galileo in the seventeenth century, the idea of sunspots did not cross the minds of people in Western civilizations—or if it did, no one ever voiced their thoughts aloud. The Sun was regarded as perfect, and if someone had suggested otherwise, they would have been disciplined or put to death. There is reason to believe that the ancient Chinese knew about sunspots and accepted their existence, having seen them, most likely, when the Sun was rising or setting in a hazy sky.

Sunspots enable astronomers to calculate the rotational period of the Sun because the blemishes seem to move across the solar disk, disappear over the edge, and then reappear a couple of weeks later on the opposite limb. The Sun rotates approximately once a month. Careful observation of spots has revealed that the Sun spins faster at lower latitudes than at higher latitudes. Using spectroscopy, this has been verified, and the solar “day” is in fact 25 Earth days long at the equator and 34 Earth days long at the poles. This fact has been used to prove that the Sun is not a solid body like Earth or the Moon.

Sunspots have an appearance that reminds some observers of biological cells (Fig. 4-10). The darkest part, at the center, is called the umbra ; it is surrounded by a brighter region called the penumbra . Sunspot sizes vary, but they can be, and often are, much larger in diameter than Earth. The spots tend to form in groups and are believed to be depressions in the solar surface resulting from magnetic disturbances. They are, in a sense, storms on the Sun. The overall average number of sunspots rises and falls in a cycle of roughly 11 years. The most recent sunspot maximum took place in late 2000 and early 2001.

The Moon and the Sun The Moon Spots And Storms

Figure 4-10. A sunspot can have a diameter greater than that of Earth.

If sunspots are like hurricanes on the Sun, then solar flares are like nuclear explosions: sudden, bright eruptions that send high-speed, charged subatomic particles flying off into space. Solar flares are more difficult to see with an ordinary telescope than are sunspots, but astronomers constantly watch the Sun for signs of these outbursts. A large solar flare is followed, in a day or so, by destabilization of Earth’s magnetic field. As the charged particles come near our planet, they accelerate toward the north and south geomagnetic poles . This acceleration produces its own magnetic field, which interacts with that of Earth. As a consequence of this, the ionized layers of Earth’s upper atmosphere change dramatically; this can create vast halos of light around the geomagnetic poles. If you happen to live at a high latitude, especially in North America, you are familiar with this glow as the aurora borealis (northern lights). Similar effects take place in the south polar regions, but the aurora australis (southern lights) are not spectacular, except as seen from Antarctica and from the far southern ocean on rare occasions when the sky over them is not socked in with grim overcast. The ionospheric disturbances affect radio communications and broadcast, especially on the so-called shortwave bands. In the extreme, even wire, cable, and satellite communications systems are disrupted by the powerful, erratic magnetic fields.

Practice problems of this concept can be found at: The Moon and the Sun Practice Problems

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