MERCURY

by: George Leal & Jerson Paul

Mercury is a terrestrial planet, which is the fourth brightest planet to the naked eye and the second closest to Earth. But being the closest planet to the Sun makes observation very difficult. Appearing over the horizon at its greatest angular distance from the Sun, it is the best time to view Mercury. This event occurs only twice a year. Although it can be seen twice a year, it must be viewed through the greatest thickness of the earth's atmosphere.

SIZE AND GRAVITY
Mercury is the second smallest planet in our solar system next to Pluto, which is the smallest. It is about one-third the size of Earth and a little larger than the moon with the diameter of 3,031 miles. It has a little more than one-third of the gravity of Earth. By weight, Mercury is 70 percent iron and only 30 percent rock.

ATMOSPHERE
The atmosphere of Mercury is very thin. This thin atmosphere that exists on the planet consists of helium and sodium. This is the product of solar wind. Its atmospheric pressure is about a million-billionth that of Earth's.

ORBIT AND ROTATION
The shortest year of any planet is held by Mercury. It takes Earth 365 days to orbit the sun, but it takes Mercury only about 88 earth days to complete one orbit around the sun. Recent radar observations show that the rotation of Mercury is about a period of 59 earth days. Mercury ratates exactly 3 times befor it orbits the sun twice, so in two of the planet's years it has only completed three of its days.