On a dark night, far from the Equator, you might be lucky enough to spot an aurora: a shimmering, colourful glow in the sky. This natural light show has captivated people for thousands of years. While it is mostly associated with cold, dark nights near the poles, auroras have a much brighter, warmer origin: the Sun.
The extremely high temperatures of the solar surface produce plasma. Plasma isn’t a gas, solid or liquid. It’s a fourth state of matter, made up of charged particles also known as ions. The stream of plasma that shoots outwards from the Sun is called the solar wind.
The solar wind travels in all directions, and Earth is constantly being bombarded by fast-moving ions from the Sun. Earth has a magnetic field, so when the solar wind hits Earth, the charged particles are attracted to Earth’s magnetic poles.
As the ions move through Earth’s atmosphere, they collide with molecules of gas, such as oxygen and nitrogen. These collisions transfer energy from the ions to the gas molecules. The molecules are now in an excited state. To come back down to their unexcited state, the gas molecules release energy in the form of coloured light. This can be seen from Earth’s surface as an aurora.
The amount of solar activity varies. Sometimes there isn’t much solar wind, and an aurora isn’t visible. Peaks of solar activity occur roughly every 11 years, and it’s been about that long since the last one. Recently some large solar flares were detected on the Sun’s surface. This evidence suggests a solar maximum is approaching, which could result in brighter and more wide-spread auroras.
It is difficult to predict when an aurora will appear, and even when one does, it can move and disappear in an instant. Science can explain many aspects of auroras. However, their elusive and unpredictable nature combined with their beauty means they still seem somewhat magical. Learn more here, here or here.