What is the Goldilocks zone?

It's a popular children's story but what does it have to do with astronomy?
It’s a popular children’s story but what does it have to do with astronomy?

Most children know the story of Goldilocks and the Three Bears; a little girl breaks into a house, finds fault with almost everything (too hot, too cold, too hard, too soft etc) and is caught by the occupants after she falls asleep in one of their beds. But Goldilocks is also important in the area of science known as astronomy. Astronomers study the stars, planets, galaxies and pretty much everything else that can be found in space. Although you might imagine an astronomer to be someone who stands out in their garden at night looking at the stars through a telescope, most astronomers these days use computers and giant telescopes. These often have names like the Very Large Telescope and the Extremely Large Telescope.

For years astronomers have been searching space for planets like our own Earth, with a temperate climate and liquid water on the surface. These planets could one day be inhabited by humans, or even give rise to life by themselves as Earth did. Scientists know that these particular planets are habitable because of the distance between them and their star. This is known as the CHZ – the circumstellar habitable zone (pronounced ser-cum-STELL-er HAB-it-abb-le zone). If a planet’s orbit takes it too close to its sun it would be too hot, while a planet that’s too far away would be too cold to be habitable. Those in the CHZ are just right, and that’s why it’s also known as the Goldilocks zone.

The CHZ varies according to the temperature of each star. (Image credit: NASA/Kepler).
The CHZ varies according to the temperature of each star. The red zone would be too hot and the blue zone too cold, but the green is just right. (Image credit: NASA/Kepler).


Every year more and more habitable planets (those in the CHZ of their star) are discovered orbiting distant stars. Based on data reported by the Kepler space observatory, there could be as many as 40 billion habitable planets in the Milky Way alone.


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