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Using the classification based on size, Mercury is one of the small planets. Along with Pluto, Mercury is sometimes also called a “lesser planet” because it is so small. Lesser planets should not be confused with “minor planets” which is the term used for asteroids.
Where is It?
Mercury is the closest planet to the sun. The orbit, or path, it takes around the sun is an ellipse, which is like an oval. For this reason, the distance from Mercury to the Sun varies from about 43 million kilometers at its closest, to about 66 million kilometers at its furthest.
How Did It Get Its Name?
Mercury is named for the Roman god of commerce and thievery. It may have received this name because of the way it quickly appears and disappears from our view
How long are its years and days?
Mercury races around the Sun faster than any other planet. A Mercurial year (the time it takes for the planet to go once around the Sun, is only 88 days, while our year on Earth is 365 days. Mercury does not spin as fast as Earth, though, so a Mercurian day (the time it takes a planet to rotate once) is 59 Earth days.
How Big Is It?
Mercury is the second smallest planet in the solar system. Pluto is the only planet that is smaller. Earth is about 12000 kilometers in diameter, while tiny Mercury is less than half that size at about 5000 kilometers in diameter. To put another way, if Earth was the size of a cricket ball, Mercury would be a little smaller than a ping-pong ball. Mercury is so small that Ganymede, one of Jupiter’s moons, and Titan, one of Saturn’s moons, are both larger.
Can It Be Seen From Earth?
Mercury can be seen without a telescope, but it is normally visible for a few days only three or four times a year. Because it is so close to the Sun, Mercury is normally hidden by sunlight. When the planet is visible, it can be seen just before sunrise just after sunset.
What Is It Like on The Surface?
Mercury has many craters on its surface. The planet has been hit many, many times through the years by asteroids and other objects. These impacts have caused all the craters on the surface. Earth probably had this many craters at one time, but our weather has worn them down over the years. The weather on Mercury varies from extremely hot to extremely cold. The temperature on the side of the planet facing towards the Sun is around 370 degrees Celsius. The “daytime” temperature on Mercury varies, depending on how close it is to the Sun. At the other extreme, the temperature on the side away from the Sun can be less than -150 degrees Celsius.
Astronomy for Kids www.dustbunny.com/afk/
Small Worlds David Drew: Nelson, 1989
The Gas Giants David Drew: Nelson, 1989
Images from: Astronomy Picture of the Day