About our Planets, Part One: the Rocks Nearest the Sun:

When we glimpse the millions of stars in the night sky, it can be difficult to imagine that some of them are planets, only thousands of miles away, and within our solar system.

However, with the proper tools, and with knowledge of the planets, you can see swift Mercury, mysterious Venus, and even the giant Jupiter from your backyard. In this first of two series on the planets of our solar system, you will learn about the planets lying between the asteroid belt and the sun. You will also learn about their special properties, and how you can distinguish them in the often star-crowded night sky. For your home astronomy activity, all you'll need are the following.

• A good pair of binoculars, preferably with very high resolution, is valuable when you want to view the planets in greater detail. You won't need a telescope if you want to see the nearest planets, although a good home telescope will show even more detail and make your observation more interesting.• Star maps are invaluable when you locate the planets, as their positions are often described in reference to nearby constellations.

• You can best view the planets in a dark place, so you need a dim flashlight to light up your star maps. Before you begin your planet hunt, there are three things you must know about our planets. According to a definition set by international astronomical organizations, a planet must be a body orbiting around the sun, and with enough mass to be a sphere due to its own gravitational forces. A planet, moreover, should clear the neighborhood around its orbit. There are other bodies within the solar system that are as large as planets, or were once considered planets, but have since been disqualified as they didn't meet one or more of the qualifications.

They won't be discussed in detail in this article. Mercury is the planet nearest the sun, and completes its revolution every eighty-eight days. Mercury has no moons, and is a very light, tiny planet. In fact, Mercury is only about 0.055 of earth in mass. Most of Mercury's thin atmosphere is made up of potassium and sodium, and its rocky surface is full of craters. The Romans were one of the first to report on the planet, which they named after their swift messenger of the gods, as the astronomers observed its fast motion in the sky. Despite Mercury's brightness, you can see it at twilight as a bright, star-like dot that doesn't twinkle. After Mercury comes Venus, a hazy planet long the subject of fiction and mystery.

Like Mercury, Venus has no moons. It is almost the same mass and size as the earth, so that the two are often referred to as "sister planets." The atmosphere of Venus, however, is about ninety-five percent carbon dioxide, and can thus support no life. Venus is the brightest heavenly body in the night sky, with the exception of our moon. It is at its brightest a few hours before sunrise, and a few hours after sunset, and is thus often called the morning star or the evening star. The Earth you now stand on is the third planet from the sun, and is the only one in our solar system known to support life. Earth has one satellite, our moon, which affects the tides of our oceans, and which, over time, has changed our planet's rotation period. Earth's atmosphere is about seventy eight percent nitrogen and twenty percent oxygen, a mixture stabilized millions of years ago, after the young, volcanic earth settled down and gave birth to life. After Earth comes the red, rocky Mars, with its two moons, Phobos and Deimos. Like Venus, the Martian atmosphere is primarily made up of carbon dioxide; unlike hazy Venus, however, Mars appears as a bright red dot in the sky. At certain times of the year, Mars is the second brightest object in the night sky, next to the moon and Venus.

Mars is red because of the iron oxide, or rust, on its surface, and recent studies have shown that it might have been home to water only a few thousand years ago. The idea that Mars may have once supported life is interesting to scientists, and Mars is promptly the planet in the solar system with the greatest number of orbiting spacecraft. Beyond Mars is a thick asteroid belt, which is also home to the dwarf planet Ceres. Once classified as an asteroid, Ceres is the smallest dwarf planet of our solar system, and comprises a third of the asteroid belt's total mass. In very good atmospheric conditions, you can see Ceres with your naked eye.

It will appear as a tiny white dot in the night sky. Tracking the planets in your backyard can be a fun activity for the whole family. Just remember that planets, unlike stars, don't twinkle, and will usually be very bright. Just keep those binoculars and star maps handy, and you can have an enjoyable night of star gazing and planet locating. For the more interesting planets, however, you will have to go beyond the asteroid belt, where the massive planets reside. These planets will be tackled in the next essay in this series.