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Ever since early humans first became aware of their environments, they have recognized the importance of the sun’s heat and light to life on the earth. People around the world have worshipped the sun as a god, and more recently the sun has been the subject of intense study by scientists. The sun is actually a star, and is described by astronomers as a rather “average” star. But the sun is much closer to the earth than any other star. The sun’s average distance from the earth is only 150 million kilometres. Although this distance is obviously very great, other stars are much farther away. At the sun’s relatively close distance, light can reach the earth in about eight minutes. The next nearest stars to the earth, however, are so far away that their light takes four years to reach the earth! Given these unimaginably vast distances, it is easy to understand why the sun seems so much brighter than any other star.
The sun is much larger than the earth or the moon. In fact, the sun’s diameter is about 110 times that of the earth, and about 400 times that of the moon. This might seem surprising, given that the sun and moon appear to be of virtually equal size when we look at them in the sky. However, the sun is about 400 times farther away from us than the moon is, and this explains why the sun and moon appear to be the same size. This fact is a remarkable coincidence, and it makes possible the occurrence of spectacular solar eclipses, when the moon seems to cover the sun almost perfectly. Note that even though the sun is a fascinating object of study, you should never look at it directly. Even if you are wearing dark sunglasses, the intense radiation from the sun can seriously damage your eyes. The sun is composed of densely-packed gases, mainly hydrogen and helium. At the core of the sun, hydrogen is transformed into helium by the process of nuclear fusion, which releases tremendous energy.
Temperatures at the sun’s core are estimated to reach 15 million degrees Kelvin; at the surface of the sun, the temperatures are much cooler, reaching only a few thousand degrees. The sun will someday use up all of its hydrogen, causing it to gradually die. But do not worry about this-scientists estimate that the sun will have enough fuel for at least another six billion years! Periodically, there are magnetic storms on the surface of the sun. Astronomers refer to these disturbances as sunspots. The activity of these sunspots sometimes causes interference with radio transmissions here on earth, and is responsible for the “northern lights” that are sometimes seen at night in northern latitudes.
The activity of sunspots seems to rise and fall in an eleven-year cycle, but there are also some longer periods of high or low sunspot activity. Scientists believe that periods with few sunspots tend to be associated with cooler temperatures on earth. Besides providing us with the light and heat that are needed for the survival of life on earth, the sun also gives us much of the beauty that we see in the world around us. Anyone who has watched the colorful sky at sunrise or sunset will surely agree!