31. Astronomers didn't realise that Mercury was a planet until 1543 when Copernicus published his Sun-centered model of the Solar System, putting the Sun as the centre of the solar system rather than the previously believed centre, the Earth.
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31. Astronomers didn't realise that Mercury was a planet until 1543 when Copernicus published his Sun-centered model of the Solar System, putting the Sun as the centre of the solar system rather than the previously believed centre, the Earth.