Explore the Solar System and the Universe
From John P. Millis, Ph.D, former About.com Guide
Solar System
Our Solar System could be called our neighborhood in our home Galaxy, the Milky Way. Explore the eight planets of our solar system and more.
Planets
A planet is a spherical ball of rock and/or gas that orbits a star. Our solar system has 8 planets; in order of increasing average distance from the Sun: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. The International Astronomy Union has an official definition for a planet. It states, "A 'planet' is defined as a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighborhood around its orbit." Pluto is a dwarf planet.
Stars
Stars are balls of mostly hydrogen and helium gas that shine extremely brightly. Learn more about stars.
- Closest Stars to Our Solar System
- Brightest Stars Seen From Earth
- Constellations Pictures Gallery
- Definition of Stars
- Pictures of Stars
Deep Space Objects
Discover the wonders of deep space. Learn more about black holes, quasars and other deep space objects.