Another unsolved mystery of the Sun is that of how fast it spins. For over three centuries astronomers have known that the photosphere rotates faster at the Sun’s equator than at higher latitudes, with a smooth variation in between. The Sun’s sidereal rotation period ranges from 25 days at the equator to 27.8 days at the +or- 40 degrees latitude, and even longer at higher latitudes. Helioseismology has recently shown, contrary to expectations, that this differential rotation persists right down to the base of the convection zone,28.7 percent of the way to the center of the sun. The equatorial rotation slows down and the high-latitude rotation speeds up at greater depths though. The two rates then become equal about half way to the center. A little farther in, the rotation appears uniform and independent of latitude; that layer of the Sun rotates like a billiard ball or another solid body. There is absolutely no explanation for this strange rotational structure. One knows that young stars begin their lives spinning rapidly, since they conserve angular momentum while contracting from large interstellar clouds. An older star, like the sun though, has showed with age. Astronomers have assumed for the longest time that magnetic field lines carried out by the stellar wind supply the braking action. They spin with the stars rotation, throwing wind particles sideways from their outer parts. If this is assumed to be correct, the Sun ought to be braked from the outside in, and the interior should be rotating more rapidly than the outer shell. This does not seem to be the case thus far. The picture is confused once one would peer more than halfway down to the center though. Some researchers report that the deep interior is spinning faster than the overlying layers; others find that the core rotates more slowly. Unfortunately, the two parts of a split frequency overlap, and the controversy will probably not be settled until SOHO or GONG obtain very long, uninterrupted stretches of low-noise data.

The Sun’s ever-changing magnetism produces gaseous activity on an enormous scale. Among many other effects, flares release stored magnetic energy equivalent to billions of nuclear explosions, raising the temperature of earth-sized regions millions of degrees. Magnetically energized coronal mass ejections, throw billions of tons of material into space. Despite this, astronomers still do not know exactly why or how these two types of eruptions occur and cannot reliably predict them.

Solar flares and coronal mass ejections flow with the Sun’s eleven-year cycle of magnetic activity. This period, as one knows from a previous in-class talk, is called the “sunspot cycle” because it was discovered from a periodic variation in the number of sunspots (blemishes that are known to be caused by intense magnetic fields). During solar maximum the Sun is heavily peppered with big, complex, often bipolar spot groups often concentrated into active regions (areas that give off intense x-rays and are prone to flares). At the sunspot minimum, smaller magnetized regions continuously swell up all over the surface. The Sun’s sporadic surface magnetism comes from a hidden generator in the inside of the Sun. Circulating gases moving through the Sun’s magnetic field produce electric currents that in turn amplify the magnetism. This same occurrence happens inside the fluid interiors of many planets and is called the dynamo effect. If there was any way to understand this effect, we might be able to explain the cyclic intense, and relaxed solar activity. Unfortunately, the models of today’s dynamos may be i

Some topics in this essay:
Observatory Ontario, Sun Earth, Sun Astronomers, EUV X-ray, SOHO GONG, Japanese Alps, Sun Inside, Sun Circulating, solar wind, center sun, solar neutrinos, , solar neutrino, coronal mass ejections, light cone, sun astronomers, ultraviolet extreme, sun’s center, cycle magnetic, ultraviolet extreme ultraviolet, sun’s magnetic,