Sunspots are regions of much higher magnetic field, and lower temperature, on the surface of the sun. They occur in an eleven year cycle, and effect our planet through the solar wind.

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Star temperature and light

When things are at different temperatures they emit different wavelengths of light, for example a piece of steel will pass through a number of colours as it is heated. The same is true of stars, and of the entire electromagnetic spectrum (not just visible light). We can use this fact to determine the temperature of the star.

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