The Solar System

A ball of fire blazed through southern Peru and left a huge crater -- and then villagers started getting sick. Early reports said the groundwater boiled and the air filled with sulfur. What happened?

By Jacob Silverman

Hundred of meteors fly across the sky every night, but only a few make it to Earth. Meteors are best known for the brilliant streaks of light they make as they burn up in the atmosphere. Learn about 10 memorable meteor crashes that left an impression.

By the Editors of Publications International, Ltd.

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.

By Craig Freudenrich, Ph.D.

Pluto is relatively round and orbits the Sun. So, why doesn't it qualify as a planet?

By Patrick J. Kiger & Kathryn Whitbourne

We know it's not made of green cheese, but what are the origins of the moon? Learn astronomers' theories about where the moon came from.

By Tracy V. Wilson

Even though it's tiny compared to the rest of the universe, Earth is a complex planet that, so far, is the only one we know of that sustains life.

By Mark Mancini

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.

The smallest and most-distant planet in our solar system is tiny, icy Pluto. It is even smaller than our moon, and wasn't discovered until 1930 — the only planet discovered in the twentieth century.

Mercury is the closest planet to the sun, and it's the smallest. So why does it have longer days than we have on Earth?

By Mark Mancini

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.

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.

Since the 1960s, we've been captivated by our planetary neighbor. How different is the planet next door, and what have we learned about it so far, compliments of the Phoenix Mars Lander and other spacecraft?

By Craig Freudenrich, Ph.D. & Nicholas Gerbis

The sun warms our planet every day, provides the light by which we see and is necessary for life on Earth. But what is it exactly, and what will happen when it burns itself out?

By Julia Layton & Craig Freudenrich, Ph.D.

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.

Where I live it is pretty common to see "shooting stars" -- streaks of light in the sky at night. How big is a shooting star? Do they land on earth or do they burn up? Do they land on the ground as meteorites?

The Chandler wobble is the change in the spin of Earth on its axis. Think of the wobble you see in a toy top when it first starts spinning or slows down. Its 'poles' do not spin in a perfectly straight line.

If I was on the moon and the earth was black (no lights were on) and a flashlight was turned on facing the moon, would I see the light? If I couldn't, would there be any way to detect any residual matter that came from the light on Earth or does light die after a certain distance?

Can the curvature of the Earth only be seen from outer space? If you didn't know that the Earth is a sphere, there are three common observations you could use to convince yourself that it is.

If "nature abhors a vacuum," then why doesn't the vacuum of space suck away all of the Earth's atmosphere?