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Scale of the Solar System: The Journey Begins

Illustration of the planets and their sizes in our solar system.
The planets are shown in the correct order of distance from the sun, the correct relative sizes, and the correct relative orbital distances.

Taking a trip away from home often helps us to understand and appreciate our own home more. NASA's Year of the Solar System invites you to take a cosmic road trip through our solar system to discover its wonders and beauty, and in the process to understand and appreciate our home, Earth.

The first step in our road trip is to get out the map and become familiar with what and where the key places are (sun, planets, moons, asteroids and comets) -- and how far apart they are. This topic focuses on some solar system basics. You are invited to participate in a walk through a scale model of a solar system and to learn about the places along the way. You will also find resources for basic information about the objects in our solar system.

More than 2,000 years ago observers
recognized special 'stars' in the night
sky. These 'stars' didn't move the way
other stars did. They wandered and
seemed to have their own timetable
separate from other stars. The Greeks
named them 'wanderers', which was
later translated to 'planet' in Latin.
Greek illustration of the planets.

For thousands of years only five planets (Mercury, Venus, Mars, Jupiter and Saturn) were visible. Observation (and much debate) finally put the planets in their proper places with the sun at the center and the planets (now including Earth) in orbits around the sun. The order was established as Mercury, Venus, Earth, Mars, Jupiter and Saturn and eventually distances were determined. As telescopes became more powerful and the math of orbits became more powerful, many new planets were discovered.

By the late 1800's every new object discovered that orbited the sun was called a planet. This included several of the larger asteroids. Powerful new telescopes and spacecraft studying solar system objects have provided more data. These data have improved our understanding of the solar system and the objects in it. This information has forced re-examination of definitions and categories of solar system objects. The definitions of planets, minor planets, dwarf planets and asteroids are still being discussed.

Through the topics within the Year of the Solar System, you will be able to explore how the solar system formed, how different objects in the solar system are from each other, how alike they are, and how we know what we know about the solar system.

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Last Updated: 12 Sep 2014