How Mars Works

NASA's rover Spirit landed successfully on Mars over the weekend and sent a message to Earth, confirming a signal lock that allows the transfer of incredible data. Learn all about the Red Planet.

How Solar Eclipses Work

A total solar eclipse is a rare event that can be an amazing thing to witness. Learn about solar eclipses and how to observe one safely.

How the Moon Works

The moon is often the largest object in the sky outside of the sun. What is the moon made of, how did it form -- and why do people blame it for their strange behavior?

How the Sun Works

Having cell phone trouble? Believe it or not, the culprit could be eruptions of charged particles on the Sun. This week saw one of the largest solar flares in 20 years. Learn all about that huge ball of light in the sky.

Why is Pluto no longer considered a planet?

On August 24, 2006, the International Astronomical Union (IAU), an organization of professional astronomers, passed two resolutions that collectively revoked Pluto's planetary status.

Jupiter Explained

Jupiter is the largest planet and is fifth from the sun. It is the third-brightest spot in our skies--after the sun and Venus. Jupiter is made up almost entirely of gas, which means it doesn't have a solid surface like Earth does.

Mars Explained

Mars, which is the fourth planet from the sun and the third smallest in size, got its name because of its rusty red color. People associated the planet's blood-red color with war, so they named it Mars, after the Roman god of war.

Neptune Explained

Neptune is the eighth planet from the sun, the fourth largest, and a gas planet. It is named after the Roman god of the sea. Neptune is four times the size of Earth, and its day lasts a little more than16 hours. Its year is about 165 Earth years. Neptune's orbit is a perfect circle. The last stop on spacecraft Voyager's epic trip through the solar system was the gas giant Neptune.

Our Amazing Solar System

Some of the most interesting objects in our solar system are also the smallest or largest. In addition to the sun, planets, and moons, our solar system has a variety of small objects such as asteroids, comets, stars, meteors, and moons. These have affected what has happened on Earth in many ways.

Uranus Explained

Uranus is the seventh planet from the sun, and is named for the ancient Greek deity of the Heavens, the earliest supreme god. It is the third largest planet in the solar system, and is three times as large as Earth.

Venus Explained

Venus is the second planet from the sun, and is about the same size as Earth. It is a terrestrial planet, meaning it has a solid surface. But the harsh conditions on Venus make it very inhospitable. Two spacecraft, Pioneer Venus 1 and Magellan, were able to penetrate the thick atmosphere of this planet.

The Solar System Explained

Our planet Earth is part of a solar system that consists of nine (and possibly ten) planets orbiting a giant, fiery star we call the sun. For thousands of years, astronomers studying the solar system have noticed that these planets march across the sky in a predictable way.

Why does the moon look so much bigger when it is near the horizon?

Why does the moon look so much bigger when it is near the horizon than when it is high up in the sky? This question has been pondered for hundreds if not thousands of years, and is commonly referred to as the moon illusion.

Earth Explained

Saturn is the sixth planet from the sun and the second largest planet in the solar system. It is named for the Roman god of agriculture, one of the most important gods in the Roman world.

Mercury Explained

Mercury is the closest planet to the sun, and it is the second smallest. It is the fastest-moving planet, so it was named after the Roman god of speed. Like Earth, it is a terrestrial planet, meaning it has a solid surface that you could land on.