What Copernicus realised, about 500 years ago and supported later by Galileo, was that our planet actually goes around the Sun, not the other way around – this made a lot of people angry because as people, we like to think we’re the centre of everything!
The idea that the Sun was in fact at the centre was revolutionary – but we know it’s true!
The time it takes for our planet to move once around the Sun is our year – 365(ish) days. A year is different for each planet; so an Earth year is longer than a year for Mercury (which is closer to the sun than we are) but shorter than a Martian year (which is further away).
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