Components of Our Solar System
This section of Astronomy is required for all GCSE Exam boards.
Our Solar System is a vast and fascinating place, a tiny part of the even vaster Milky Way galaxy. It consists of several key components, all held together by gravity:
- The Sun (Our Star): At the very centre of our Solar System is the Sun. It’s a medium-sized star, and it’s by far the largest object in our system, containing over 99.8% of the total mass. The Sun generates its own energy through nuclear fusion in its core, releasing immense amounts of light and heat. This energy is essential for life on Earth and influences all the other objects in the Solar System.
- Eight Planets: Orbiting the Sun are eight planets. These are large celestial bodies that orbit a star. Planets are massive enough for their own gravity to make them nearly round, and have cleared the neighbourhood around their orbit.
- Natural Satellites (Moons): Many planets have natural satellites, or moons, orbiting them. Our Earth, for example, has one natural satellite – the Moon. Other planets, like Jupiter and Saturn, have dozens of moons, some of which are larger than dwarf planets.
- Dwarf Planets: These are celestial bodies that orbit the Sun, are nearly round due to their own gravity, but have not cleared the neighbourhood around their orbit. The most famous dwarf planet is Pluto, but others include Ceres (in the asteroid belt) and Eris.
- Asteroids: These are small, rocky, irregular-shaped bodies that also orbit the Sun. Most asteroids are found in the asteroid belt, a region between the orbits of Mars and Jupiter. They are essentially ‘leftovers’ from the early formation of the Solar System.
- Comets: Comets are icy, rocky bodies that orbit the Sun, often in very elliptical (oval-shaped) paths. As a comet approaches the Sun, the ice turns directly into gas (sublimation), creating a glowing coma (a dusty atmosphere) and often a distinctive tail that points away from the Sun.
The Eight Planets in Order
It’s important to know the names of the eight planets and their order of distance from the Sun. Remember, the further away from the Sun a planet is, the longer its orbital period (the time it takes to complete one orbit).
Here they are, from closest to furthest from the Sun:
- Mercury
- Venus
- Earth
- Mars
- Jupiter
- Saturn
- Uranus
- Neptune
A popular mnemonic to help you remember this order is:My Very Excellent Mother Just Served Us Noodles.
Orbits of Celestial Bodies and Artificial Satellites
An orbit is the curved path an object takes around another object due to gravity.
- Moons Orbiting Planets: Natural satellites (moons) are held in orbit around their parent planets by the force of gravity. For instance, the Earth’s Moon orbits the Earth.
- Planets Orbiting the Sun: Similarly, planets are held in orbit around the Sun by the Sun’s immense gravitational pull.
- Comets Orbiting the Sun: Comets also orbit the Sun, but their orbits are often highly elliptical (oval-shaped), meaning their distance from the Sun varies greatly throughout their orbit. Some comets can take hundreds or even thousands of years to complete one orbit.
- Artificial Satellites Orbiting Earth (or other bodies): These are man-made objects launched into space to orbit Earth or other celestial bodies. Examples include communication satellites, weather satellites, and the International Space Station (ISS). They are placed into orbit at specific altitudes and speeds to counteract the Earth’s gravity, effectively falling around the Earth without hitting it.
All these orbits are generally elliptical, though many planetary orbits are very close to being circular. The force of gravity provides the necessary centripetal force to keep objects in their curved paths.