An aurora is a natural light display in the sky, particularly in the polar regions, caused by the collision of charged particles directed by the Earth’s magnetic field. An aurora is usually observed at night and typically occurs in the ionosphere. It is also referred to as a polar aurora or, collectively, as polar lights. These phenomena are commonly visible between 60 and 72 degrees north and south latitudes, which place them in a ring just within the Arctic and Antarctic polar circles. Recent increases in solar activity, including the largest solar flare in four years, may lead to hopes of seeing the aurora borealis, also known as the northern lights, in the United Kingdom and other relatively more southern locales. In the United Kingdom, for example, the chances of seeing the aurora increase the further north you go – ranging from one or two displays every 10 years in the south of England to one or two displays a week in the far northern Shetland Islands. Solar variation is the change in the amount of radiation emitted by the Sun and in its spectral distribution over years to millennia. These variations have periodic components, the main one being the approximately 11-year solar cycle (or sunspot cycle). This variation causes the northern lights to vary in location and magnitude.