If you live in a high latitude country like Norway, Sweden, Finland, Greenland, or Canada, you're probably familiar with the aurora borealis, otherwise known as the Northern Lights. These ethereal light shows look so otherworldly that before modern science, people created myths to explain them. Some Inuit peoples believed the spirits of their ancestors would dance in the lights. The Norse people thought the northern lights were a fire bridge fridge to the sky. Of course, today, we understand the science behind those flickering bands of green, pink, red, and blue light across the sky. But what exactly is an aurora, and how does it work?
To understand what an aurora is, we have to start with the Sun. Our Sun is a colossal 93 million miles away from Earth, but it significantly impacts our planet despite its distance. The Sun is essentially a giant nuclear power plant where temperatures and pressures are so high that hydrogen atoms are squeezed together to become helium atoms. This process releases energy in the form of heat, light, and charged gas (plasma). The charged gas makes its way to the Sun's surface, where it sometimes creates strong magnetic fields. If there is enough gas and a strong enough magnetic field, the magnetic field will stretch and eventually snap, breaking off from the Sun and hurtling into space. This is known as a coronal mass ejection, a type of solar storm1.
When the plasma reaches Earth after around 12 hours, it interacts with the Earth's magnetic field. The magnetic field surrounding Earth deflects the charged gas up or down the planet, forcing the gas to travel down the magnetic field lines of the north and south poles and into the atmosphere.
The colours you see in the Aurora are directly related to the type of atom that was excited. How Are the Colours of the Aurora Created?
When the high-energy particles (usually, electrons) enter Earth, they interact with neutral atoms in the upper atmosphere. This interaction causes the electrons in our atmosphere to become excited. When the electrons return to their original state, they emit visible light of varying wavelengths.
The colours you see in the Aurora are directly related to the type of atom that was excited. Since the Earth's atmosphere is composed chiefly of Nitrogen and Oxygen, these are the atoms and molecules that become excited. Ionised Nitrogen produces purple and blue flames of light. Oxygen atoms in their excited state produce green, yellow, and red light; and Nitrogen molecules in their excited state produces deep red hues.2
No! As a general rule, if a planet has a magnetic field and an atmosphere, they will experience auroras too. Planetary scientists have captured some stunning auroras on Saturn and Jupiter, for example.3
Most people are more familiar with the Northern Lights (aurora borealis) than the Southern Lights (aurora australis), but why? The Southern Lights are much harder to see because of the lack of accessible land in the Southern Hemisphere. You would be able to see aurora australis in Antarctica, but most cruise ships only visit the continent in the Summer months, where daylight hours can be as long as 24 hours. However, you can see the Southern Lights from some locations in New Zealand and Tasmania. The best time to spot the Northern Lights is November and December.
The Solar Cycle also has an impact on when you can see auroras. The Sun goes through cycles that last approximately 11 years, and solar storms are most prevalent when the Sun is in the Solar Maximum stage of the cycle.4 The Sun's next solar maximum is predicted to be in July 20255, and the auroras are typically more active two to three years on either side of the maximum.
You may review the infographics on auroras below: