Star or planet? When you look up into the sky, it’s fairly easy to spot the difference between a star (the sun) and a planet (the earth). But what actually are the differences between stars and planets? Talk to your partner about what you already know.

Stars The definition of a star is “A huge collection of gases that are held together by gravity.” A star creates and then releases LOADS of energy as light and heat energy because the core of the star is so hot. It’s a bit like a super-hot light bulb, giving off heat and light.

The most obvious star in our solar system is The Sun: Stars The most obvious star in our solar system is The Sun: The huge pressures inside the big ball of gas are then released in the form of heat and light. The Sun is SO big and heavy that because of gravity it pulls in lots and lots of gas, mainly helium and hydrogen.

Ok, so what do we know about planets? How are they different to stars? Stars are really bright, thanks to the huge amounts of energy being created in the middle of their massive, dense centres. So when you look into the sky, you’re probably seeing stars (possibly from very far away) rather than planets. Stars are really bright, thanks to the huge amounts of energy being created in the middle of their massive, dense centres. So when you look into the sky, you’re probably seeing stars (possibly from very far away) rather than planets. Ok, so what do we know about planets? How are they different to stars?

Planets Planets are still large objects, but usually they are made of much more rocky materials. Some planets can be made of gas (like a star), but the big difference between the two is that planets don’t have anywhere near as much gravity. You see, the sheer size of stars create a HUGE amount of gravitational pull, something a planet could never achieve. That means that planets almost always orbit stars.

Planets This video might give you a better understanding of how much bigger stars can be than planets… Video

Some key facts Planets and stars are both observable to the human eye. Stars are just easier to see because they are so bright. Stars are large collections of gas that have huge pressures like a furnace at their core, whereas planets can be large but lack the same immense pressures. Planets aren’t stars due to their lack of mass; they are simply nowhere near big enough for their centre to become hot enough to start creating the pressures needed to give off heat or light energy. Take Jupiter as an example, it seems huge but it’d need to be 80 times bigger for it to be large enough to start producing energy!

Task So there are some very big differences between stars and planets, but both also have similarities. Use the netbooks and topic-books to research some more differences and similarities between the two. Use a Venn Diagram in your Science books to show what you have found: Planets Stars Both / similarities