Nine Planets - Solar System Tour

This website is an overview of the history, mythology and current scientific knowledge of the planets, moons and other objects in our solar system. Each page has our text and NASA's images, some have sounds and movies, most provide references to additional related information.

Solar System

Please visit our Astronomy news section which gives news, notes and general observations, we also have an interactive tour of the solar system (loads in a new window)

All planets can be seen with a small telescope or binoculars and private observatories continue to provide useful information. But the possibility of getting up close with interplanetary spacecraft has revolutionized planetary science. Very little of this site would have been possible without the space program.

Nevertheless, there's a lot that you can see with very modest equipment or even with just your own eyes. Past generations of people found beauty and a sense of wonder contemplating the night sky. Today's scientific knowledge further enhances and deepens that experience. And you can share in it by simply going out in the evening and looking up.

The Sun

The Sun is by far the largest object in the solar system. It contains more than 99.8% of the total mass of the Solar System (Jupiter contains most of the rest). It is often said that the Sun is an "ordinary" star. That's true in the sense that there are many others similar to it. But there are many more smaller stars than larger ones; the Sun is in the top 10% by mass. The median size of stars in our galaxy is probably less than half the mass of the Sun.


Jupiter is the fourth brightest object in the sky (after the Sun, the Moon and Venus). It has been known since prehistoric times as a bright "wandering star". But in 1610 when Galileo first pointed a telescope at the sky he discovered Jupiter's four large moons Io, Europa, Ganymede and Callisto (now known as the Galilean moons) and recorded their motions back and forth around Jupiter.


In Roman mythology Mercury is the god of commerce, travel and thievery, the Roman counterpart of the Greek god Hermes, the messenger of the Gods. The planet probably received this name because it moves so quickly across the sky. Mercury has been known since at least the time of the Sumerians (3rd millennium BC).

The IAU changed the definition of "planet" so that Pluto no longer qualifies. There are officially only eight planets in our solar system. Of course this change in terminology does not affect what's actually out there. In the end, it's not very important how we classify the various objects in our solar system. What is important is to learn about their physical nature and their histories.

Planet Order from the Sun; Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune

Our knowledge of our solar system is extensive but it is far from complete. Some of the worlds have never even been photographed up close. The Nine Planets is an overview of what we know today. We are still exploring, much more is still to come:

We shall not cease from exploration, and the end of all our exploring will be to arrive where we started and know the place for the first time.
-- T. S. Eliot

Other Educational Resources & Notes

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