Aurora

An aurora is a beautiful natural light show that happens high up in Earth's sky. It occurs when tiny charged particles from the Sun crash into atoms in Earth's upper atmosphere. These crashes make the atoms glow, creating lovely colors like green, red, and purple.

When you see these glowing lights in places far north or south, they are called polar lights. In the north, they are known as the northern lights or aurora borealis, and in the south, they are called the southern lights or aurora australis. The lights can look like moving curtains, thin lines, or spinning shapes that fill the sky.

Auroras happen because of changes in Earth's magnetic field caused by fast-moving particles from the Sun. These changes send electrons and protons into the upper atmosphere, where they make the air glow. Many other planets and even some moons in our Solar System also experience auroras.

Etymology

The term aurora borealis was first used in 1649 by Pierre Gassendi to describe a bright light display seen all over France in 1621. The word aurora comes from the Roman goddess of the dawn, Aurora, who would travel from east to west to announce the rising of the Sun. Words like borealis and australis come from ancient gods of the north and south winds, Boreas and Auster or australis, in Greco-Roman mythology. Today, scientists often use the plural aurorae, but many people simply say "auroras."

Characterisation

Auroras are beautiful lights that appear in the sky, mostly near the north and south poles. They happen when particles from the Sun hit atoms in Earth's upper atmosphere, making them glow in colors like green, red, and purple.

These lights are usually seen in special areas called the "auroral zones," which are about 6 degrees wide and centered around 67 degrees north and south. In the north, they are called the aurora borealis or northern lights, and in the south, the aurora australis or southern lights. These lights can sometimes be seen much farther from the poles during strong solar storms.

Causes

The main reason auroras appear is because of the interaction between the solar wind and Earth's magnetosphere. The solar wind, a stream of charged particles from the Sun, collides with Earth's magnetic field. This can cause beautiful light shows in the sky.

These lights happen when particles from the Sun hit atoms of oxygen and nitrogen in Earth's upper atmosphere. The collisions excite these atoms, and when they return to their normal state, they glow. Oxygen makes green and red lights, while nitrogen can make blue and purple lights. The colour of the aurora depends on the type of atom and how high up in the atmosphere the reaction happens.

Interaction of the solar wind with Earth

Earth is always surrounded by the solar wind, a stream of charged particles from the Sun. These particles travel at high speeds and carry a magnetic field. When they reach Earth, they interact with our planet's magnetic field, creating beautiful lights in the sky called auroras.

The solar wind comes from the Sun's hot outer layer and moves outward in all directions. It can change in strength and speed, especially during events like coronal mass ejections. When the solar wind is stronger, auroras become more frequent and brighter. The way these particles connect with Earth's magnetic field plays a key role in creating the colorful auroras we see.

Auroral particle acceleration

Auroras happen when particles from the Sun hit Earth's atmosphere. There are two main types: diffuse aurora and discrete aurora. Diffuse aurora look fuzzy and less defined, while discrete aurora have clear shapes like arcs and rays.

These particles start trapped in Earth's magnetosphere. They move along magnetic field lines but are usually stopped by a magnetic mirror. Sometimes, their direction changes because of plasma waves, allowing them to hit the atmosphere and create diffuse aurora. For discrete aurora, strong electric fields push the particles toward Earth, giving them more energy and creating bright, defined shapes.

Historically significant events

In 2017, a diary from 1770 was found in Japan, showing auroras above Kyoto. This suggested a big storm might have been even larger than the Carrington Event.

The auroras from the Carrington Event in August and September 1859 were some of the most amazing ever seen. People all over the world reported seeing them. In Boston, the aurora was so bright that people could read by its light! Scientists learned a lot from this event, especially how auroras and electricity are connected.

In May 2024, solar storms made the aurora visible as far south as Ferdows, Iran.

Historical views and folklore

People have noticed auroras for thousands of years and created many stories about them. The oldest written record comes from ancient China around 977 or 957 BC, mentioned in the Bamboo Annals. The ancient Greek explorer Pytheas wrote about them in the 4th century BC, and the Roman philosopher Seneca described them with many colorful names.

Different cultures saw auroras in unique ways. In Japanese folklore, some thought "red pheasant tails" in the sky were special lights. Aboriginal Australians often linked auroras to fire, with names like puae buae meaning "ashes." In Scandinavia, people in the 1230s called them norðrljós, or the northern lights.

Many traditions around the world connect auroras with spirits or ancestors. Some Native American groups, like the Chipewyan Dene, saw them as spirits of friends dancing in the sky. These fascinating lights have inspired stories and wonder for centuries.

Extraterrestrial auroras

Aurorae have been observed on planets with magnetic fields, except for Neptune. The way they work is similar to Earth's, but they can look quite different. Both Jupiter and Saturn have much stronger magnetic fields than Earth, and their auroras have been studied using telescopes and spacecraft like the Hubble Space Telescope, Cassini, and Galileo.

Jupiter's auroras are especially interesting because they are influenced by its volcanic moon Io and its strong magnetic field. Auroras have also been seen on Venus, Mars, and even on a comet named 67P/Churyumov–Gerasimenko. These auroras happen when particles from the Sun collide with the atmospheres or surrounding gases of these celestial bodies.