Sunspot formation and evolution, illustration. Sunspots (black dots) are areas of magnetic activity that are cooler than the rest of the Sun's surface. They range in size from hundreds to thousands of kilometres across. Sunspots form where magnetic field lines (red) become twisted and entangled due to a faster speed of rotation (blue lines) at the Sun's equator compared to higher latitudes. This distortion of the magnetic field lines is shown in the first three images in this sequence, from upper left to upper right. Loops of magnetic field rising from the Sun's surface converge at regions known as sunspots. Across bottom, the further evolution of sunspots is shown. At lower left, sunspots move closer to the equator as the magnetic field lines are pulled tighter together. Eventually, the magnetic field breaks down (lower centre), and sunspots of opposite polarity cancel each other out. At lower right, the magnetic field starts to reform, with the north-south polarity reversed.