Solar System model on a city map

Introduction to the Solar System

The Solar System is home to a star located at its center and to eight planets including Earth. These planets orbit around the Sun and present variations in size and composition. The Solar System is located in the Milky Way galaxy along with a vast number of stars. The great distances between the stars are almost unimaginable along with the location of the Solar System in the Universe. Compared to these distances, the planets of the Solar System are close, but compared to distances on Earth, it becomes difficult to visualize them. The distance between Pluto and the Sun is about 5.9 billion kilometers!

Sun and planets in the solar system: (teachers are encouraged to share these information while conducting the activity)

• The Sun is the closest star to Earth consisting of electrically charged particles and mostly composed of hydrogen and helium. More than one million Earths could fit into it. The Sun is a middle sized star powered by nuclear fusion. It takes about 8 minutes for the sunlight to reach Earth after being emitted from its surface.
• Mercury is the nearest planet to the Sun and also the smallest in size. Since the planet lacks of an atmosphere, it experiences both hot and cold extreme temperatures. Out of all the terrestrial planets in the Solar System, Mercury is the densest planet.
• Venus is the hottest planet of the Solar System and is very close in size to Earth. The planet possesses a very dense atmosphere of mainly carbon dioxide that causes it to reach the highest temperatures of all the planets (740 Kelvins at the surface while Earth is about 290 Kelvins!). Venus is nearly covered by a thick layer of sulphuric acid clouds that prevent the solar rays to penetrate in the atmosphere below.
• Earth is the only planet known so far to support life. It has a magnetic field that extends thousands of kilometers into space and protects the planet from harmful incoming solar radiation. The planet is located at the center of what astronomers call the habitable zone, where temperatures are suitable enough for water to exist in its liquid state.
• Mars presents frozen water in its polar caps. Several flybys, landers, orbiters, and rovers have been sent to Mars to study the planet. However, one of the biggest questions about the planet still remains open: did water ever exist on Mars?
• Jupiter is the largest planet of the Solar System and is the first among the gaseous planets. It contains more than twice the mass of all the planets of the Solar System together. The planet is so large enough that 1400 Earths can fit into it.
• Saturn is well known for its bright rings. Saturn needs about 30 Earth years to orbit the Sun but only about 11 hours to rotate around its axis. Its rings are composed of billions of icy and rocky materials.
• Uranus is known as an ice giant planet since is composed of relatively great amounts icy methane and water. Uranus rotation axis is tilted almost parallel to its orbital plane while the rest of the planets spin more or less perpendicular to the plane of the Solar System.
• Neptune is the most distant planet of the Solar System. It is roughly half as far from Uranus as Uranus is from the Sun. Like Uranus, Neptune has rings that are thin and which consequently appear very dim when observed.
• Other bodies:
  • The Moon is Earth's only natural satellite and it was visited for the first time by the Apollo 11 landing mission in 1969. The dark and relatively featureless lunar areas that can be clearly seen with the naked eye are called maria, which are known to be the result of ancient balsatic lava.
    
  • The asteroid belt is a region of the Solar System found between the orbits of Mars and Jupiter and it is occupied by asteroids of different shapes and sizes. Asteroids are rocky-metallic objects which are also called planetoids or minor planets because they are too small (they can range from the size of pebbles to ~ 1000 km).
    
  • Comets are icy small bodies that have a wide range of orbital periods. When passing close to the Sun, comets heat up and outgas material giving it the shape of a snowball with a tail. They are known to have a wide range of orbital periods.
    
  • Pluto is a dwarf planet found in the Solar System. Since its discovery in 1930, Pluto remained classified as a planet until the detection of the more massive body Eris put it in question. In 2006, the definiton of a planet stated by the International Astronomical Union excluded Pluto since it failed to clear out the neighbourhood objects from its orbit.

Astronomical unit (au): Is a unit of length, approximately the distance between the Earth and the Sun, astronomers use to describe the great distances in the Solar System.

The scale factor:

In a scale model, all linear distances and sizes are enlarged or reduced by a scaling factor. The scale factor is given by; scale factor = true value/reference value

For example, when scaling the Solar System, the diameter of Earth and the reference size (in this case is a peppercorn of 2 mm) could be used as the true and reference values, respectively. In order to scale the rest of the planets, their true sizes and the scale factor calculated above are used:

scale model = true value/scale factor

Example of a scaled model of the Solar System on the city map of Munich showing the orbits of Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune around the Sun (located at the city center in Marienplatz, Munich, Germany).