Our solar system consists of the sun, the nine planets and their moons, asteroids and comets. The applet below shows the orbits and positions of the planets right now. Click and drag your mouse to tilt or rotate the solar system. Shift+Click zooms in and Ctrl+Click zooms out.
Note: The orbits of the planets are shown to scale, but the sun and planets themselves are much larger than scale so you can see them easily.
The inner planets (Mercury, Venus, Earth, and Mars), are relatively small and made primarily of rock and iron. The asteroids orbit the sun in a belt beyond the orbit of Mars, tumbling and sometimes colliding with one another. Made mostly of rock and iron, the asteroids may be the remnants of a planet that never formed. The outer planets, with the exception of Pluto, are much larger and made mainly of hydrogen, helium, and ice. Many astronomers believe that Pluto was an interstellar wanderer that was captured by the Sun's gravity and was not an original part of the solar system.
The planets move around the sun in fairly circular orbits (i.e., they are elliptical orbits with low eccentricity). Use your mouse to click and drag on the solar system above until you are looking straight down on the planets' orbits. Now zoom in and out to see how all the orbits are very circular, except for Pluto's!
Again with the exception of Pluto, the planets all orbit the sun in almost the same plane. Using your mouse again, drag the solar system image until you are looking at the orbits edgewise. You can see how well they line up.
The average distance of the earth to the sun is used as a standard for measuring distances in the solar system and is called an astronomical unit (AU). One AU is about 93 million miles or 150 million kilometers. Mercury, the planet closest to the sun, is at about 0.387 AU. Pluto is the outermost planet, and is 39.44 AU from the sun. The boundary between the solar system and interstellar space is called the heliopause, and is about 100 AU from the sun. Some comets have highly eccentric orbits, and can travel out as far as 50,000 AU from the sun.
Applet and text courtesy NASA.
