Mercury

Mercury is the smallest of our neighboring planets. It is only one half of Earth's size. There is no air on Mercury to block out the suns extreme heat. This causes the surface temperature on Mecury to reach 400 degrees C. Mercury looks similar to out moon with its craters. The planet is barren and rocky, with little or no vegetation and no atmosphere. Gravity is weak. A human weighing 100 pound on Earth will weigh only 38 pounds on Mercury. The distance from Mercury to the sun is 36,000,000 miles. The planet rotates slowly. A mercury day is long, about 59 Earth days. Mercury moves swiftly around the sun. One revolution, a mercury year is only 88 Earth days.

With no atmosphere to even out temperatures, the planet is usually very hot or very cold Surface temperatures usually may be 800 degrees F during the day and -280 degrees F at night. Due to the amount of heat and radiation from the sun, the landscape may be glazed with cinders. Landforms help scientists to tell some of the history of Mercury. The planet is covered with deep craters created when large meteorites crashed into it billions of years ago. The largest crater is the Caloris Basin, a low-lying area about 800 miles across and ringed with mountains. The planet also has scarps, ridges of cliffs that were probably pushed up when the planet shrank after its formation.

Mercury is difficult to see because it is very close to the sun. It is seldom visible except just before sunrise or just after sunset. It is also visible when Mercury is at its highest angle away from the sun. Mercury was named for the Greek god Mercury who had wings on his feet and was known for his speed. Mercury makes the shortest and fastest orbit around the sun. Due to Mercury's orbit it passes between the earth and the sun. It shows phases as does the moon. With a telescope some od these phases can be seen. Mercury is especially visible during the crescent phase. Mercury has no known moons and is the fourth brightest planet to the naked eye. Mercury was visited by Mariner 10 in 1974.

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