Rights: © Copyright 2009. University of Waikato. All Rights Reserved. Published 1 April 2009 Download

Dr Melanie Johnston-Hollitt, from Victoria University of Wellington, explains the difference between planets and stars, and the place of the Solar System in our galaxy.


In the simplest terms what constitutes a planet is that it’s a piece of rock orbiting a star. A star is usually a gas ball which has its own internal heat and its burning and it emits its own light, whereas planets don’t. Planets are much smaller, they go round stars. And a solar system is basically one star which has a number of planets orbiting around it.

So our solar system has got the sun as its star and it’s got these planets going around it, including Earth. And our solar system is embedded in a galaxy of many, many other stars. And, in fact, we know now that other stars also have other planets and so other solar systems and that’s all in our own galaxy.