This term, we will be learning about the planets and our solar system.
How many planets are in our solar system?
Who was the first person to walk on the Moon? When was this?
How do we have seasons on Earth?
What are forces and what are their effects?
Who was an important scientist in this area of science?
What is a planet?
Not everyone agrees on what the definition of a planet should be. The most recent definition of a planet was defined in 2006 by the International Astronomical Union. It says that a planet:
must orbit a star (in our solar system, this is the Sun)
must be roughly spherical in shape
must be big enough that its gravity is big enough to clear away any other objects of a similar size near its orbit around the Sun.
Until 2006, Pluto was considered to be a planet but then its status was changed to ‘dwarf planet’. This is because it does not meet the last of the three criteria – it hasn’t cleared its neighbouring region of other objects because its gravitational force isn’t big enough.
What is the universe?
The Universe is everything! It comprises everything we can see, hear, touch and detect. The Universe is enormous – it’s so big that we can’t even see the edge of it, if there even is one. The part of the Universe we can see is at least 93 billion light years across. A light year is the distance light travels in a year (about 9 trillion kilometres). So multiply 9 trillion kilometres by 93 billion and that’s how big the visible Universe is!
What is the solar system?
The solar system is a system of stars, planets and other objects that are all gravitationally bound to the Sun. In other words, the solar system includes anything that orbits the Sun because the movement of the planet balances with the gravity of the Sun to keep the objects moving around the Sun.
Our solar system consists of the Sun (a star), the planets Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune, dwarf planets such as Pluto, lots of moons and millions of asteroids, comets and meteoroids.
What is a galaxy?
The Universe is made up of billions of galaxies. A galaxy is a collection of dust, gas, billions of stars and their solar systems. A galaxy is held together by gravity. Galaxies can be all sorts of different shapes, sizes and colours. There are so many galaxies in the universe that we can’t even count them all yet!