The Sun is a source of heat and light without which earth would be lifeless. It is a huge gaseous ball of 865,000 miles in diameter. Its inner temperature is measured in millions of degrees, and disturbances on its surface send streams of glowing gas tens of thousands of miles into space. The source of all of sun’s energy lies far below its visible surface, in its thermonuclear core. Temperatures in the core reach nearly 30,000,000 degree Fahrenheit, and pressures are so enormous that the gases there (mainly hydrogen and helium) are compressed to a density 14 times that of lead. Under so much heat and pressure, the hydrogen is transformed into helium in thermonuclear reactions that release massive amounts of energy. The energy then passes through a thick zone of hot gases that blankets the inner core, and it eventually reaches the sun’s surface, where it is radiated into space as heat and light.
On long days of summer, the midday sun is high in the sky and its rays beam directly on the ground. In winter, days are short. The sun does not climb as high in the sky and its low slanting rays are spread out over much larger areas. That is why it is hot in summer and cold in winter.
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