Credit : wired
The first evidence that the sun is changing comes from studies of sunspots, which are large, dark features seen on the sun’s surface from increased magnetic activity. They look darker because the spots are typically around 3800 K, while the surrounding light areas are around 5800 K. Occasionally, these spots are large enough to be visible to the naked eye., and we have records dating back over a thousand years when observers noticed them when haze or mist reduced the intensity of the sun..(We emphasize what your parents must have told you: Even a quick look in the sun can cause permanent eye damage. This is the only area of astronomy where we do not encourage you to make your own observation without careful instruction or filters from you. Teacher.)
Although we know that sunspots look darker because they are cooler, they are still hotter than the surfaces of many stars. If they could be removed from the sun, they would shine brightly. They just appear dark in contrast to the hotter and brighter photosphere that surrounds them.
Individual sunspots come and go, with a lifespan of a few hours to a few months. When a spot persists and develops, it generally consists of two parts: a darker inner core, the umbra, and a less dark surrounding area, the penumbra. Many spots become much larger than the Earth, and some, like the largest, have reached over 140,000 kilometers in diameter. The spots often appear in groups of 2 to 20 or more. The largest groups are very complex and can have more than 100 seats. Like storms on Earth, sunspots are not stationary, but rather move slowly compared to those of the sun’s rotation.
credit: modification of work by SOHO/NASA/ESA
By recording the apparent movements of sunspots as the rotating sun carried them across its disk, Galileo showed in 1612 that the sun rotates around its axis with a period of rotation of about a month. Our star rotates like the orbital in a west-east direction. Movements of the planets. However, the sun is a gas and does not have to rotate rigidly like a solid body like the earth. Modern observations show that the speed of rotation of the sun varies with latitude, that is, how you go north or south of the sun equator is different. The rotation time is about 25 days at the equator, 28 days at latitude 40 ° and 36 days at latitude 80 °.We call this behavior differential rotation.
Sunspot Cycle
Between 1826 and 1850 Heinrich Schwabe, a German pharmacist and amateur astronomer, kept daily records of the number of sunspots. What he was really looking for was a planet in orbit of Mercury, which he hoped to find by watching its dark silhouette as it passed. between sun and earth. He couldn’t find the planet he expected, but his diligence paid off with an even more important discovery: the sunspot cycle. He found that the number of sunspots varied systematically in cycles of about a decade.
Schwabe observed that although individual spots are short-lived, the total number visible on the sun at any given point in time is likely to be much higher at certain times Periods with maximum sunspots than at other times, periods with minimum sunspots.. We now know that sunspot maxima occur at an average interval of 11 years, but the intervals between consecutive maxima varied from as little as 9 years to 14 years. During the sunspot maximum, more than 100 sunspots can often be seen at the same time. so less than half a percent of the sun’s surface is covered with spots. Sometimes no spots are seen during the sunspot minima. The activity of the sun reached its last peak in 2014.
