Auroras: Spectacular Light Shows

Have you ever looked up at night and seen a shimmering curtain of lights in the sky? If so, you’re pretty lucky! Auroras are only visible at certain times and places on Earth.

What do auroras look like?

Earth’s atmosphere contains different types of gases. These gases can emit light when they collide with high-energy particles from the Sun. The colour of the light depends on the type of gas. It also depends on the altitude at which the collisions occur.

Green is one of the most common colours in auroras. This happens when particles collide with oxygen molecules between 100 and 300 km above Earth. Pink and dark red colours happen when particles collide with nitrogen molecules at about 100 km. Finally, blue and purple are caused by hydrogen and helium. These colours can be hard to see against the dark night sky.

Did you know?

Auroras can be seen from space. Astronauts can get a close up view! You can see it yourself by watching this video taken from the International Space Station.

Where can you see auroras? 

Auroras are typically seen near the Earth’s poles. We call the auroras near the north pole aurora borealis, or northern lights. We call the auroras near the south pole aurora australis, or southern lights.

Aurora borealis can be seen in northern parts of Earth’s northern hemisphere. This area includes parts of Canada, Alaska, Russia, Norway, Finland, Sweden, Iceland and Greenland.

Auroras appear most often between 60 and 75 degrees north latitude. In Canada, this includes communities in Yukon, Northwest Territories and Nunavut. But sometimes they can be seen further south, around 50 degrees. Communities near this latitude include Calgary, Regina, Winnipeg, and Happy Valley-Goose Bay.

Image - Text Version

Shown is a colour diagram of Earth with a thick, bright green oval. The title, “Tonight’s Aurora Forecast” is in yellow letters at the top left, next to the name and logo of the NOAA Space Weather Prediction Centre. Smaller text below reads: “Forecasted Kp:3 (Range 0-9), Forecasted G-Scale: 0 (range 0-5).” A legend below shows a spectrum labelled “Likelihood of Aurora.” The colours range from black on the left, through green, yellow, and orange, to red on the right. The globe is shown with the northern hemisphere and North America in view. A thick, wide streak of bright green loops around the North Pole, across Alaska, most of Canada, southern Iceland and northern Greenland. In the lower right corner, a line of text reads: “Creation Time: 2023-10-26 17:55:14.”

Aurora australis are only visible in a few places on Earth, and some of them are pretty remote. This may be why the southern lights are less well-known. They can be seen from the southernmost parts of Australia and Argentina, as well as New Zealand, South Georgia Island and Antarctica!

Did You Know?

Historians think the furthest south the northern lights have ever been seen is in Honolulu, Hawaii. That is only 21 degrees north of the equator! This aurora was seen during the great solar storm of 1859. The southern lights may have been seen as far north as Singapore, eight degrees south of the equator.

When are they visible? 

This is an important question! Sometimes, people who don’t live in the range of auroras will travel long distances to see them. There is a whole tourist industry devoted to aurora-spotting!

The northern lights are visible for more days each year the further north you go. The same applies to the southern lights. So, if you live in Nunavut, you could see them between October and April each year. If you’re lucky enough to go to Antarctica, you could see them between March and September, during the Antarctic winter.

How do they happen?

Like other magnets, Earth generates a magnetic field. The field extends from the Earth’s core, out into space, and back again. It starts in the southern part of the planet and ends in the northern part of the planet.

The path of the field is often represented in illustrations, like the one on the right, as magnetic field lines. These form a bubble around the globe with deep dimples at the north and south poles.

The region influenced by the magnetic field around the Earth is what scientists call the magnetosphere.

Image - Text Version

Shown is a colour diagram of Earth surrounded by the bubble that is the magnetosphere. The title, “Earth’s Magnetic Field” is at the top of the image. Below, Earth is in the middle of the illustration. At its centre, there is an illustration of a rectangular magnet, half blue and half red. A straight dotted line leads from each end, out through the top and the bottom of the globe. The points where these exit Earth’s surface are labelled “Magnetic North Pole” and “Magnetic South Pole.” Other dotted lines with small arrows along them, fan out from the bottom of the magnet, around the Southern Hemisphere and far out into space. Then they curve back towards the Northern Hemisphere, meeting again at the top of the magnet. These lines are labelled “Magnetic Field Line.” The area inside the lines is labelled “Magnetosphere.” Through the centre of the globe, tilted at an angle to the magnet, is a thin yellow line. This is labelled “Earth’s Axis.” Curved blue arrows around the top and bottom indicate Earth rotates around this axis. The points where this rod exits Earth’s surface, in the Northern and Southern Hemispheres, are labelled “Geographic North Pole” and “Geographic South Pole.” Beyond this, space is shown as dark blue, with the dark grey Moon in the lower left corner.

The shape of the magnetosphere steers solar particles towards the poles. Here, they form auroral ovals. These are bands of aurora activity. But auroral ovals are not always the same shape or size. Why is this?

The solar particles travel to Earth in solar wind. These winds push on the magnetosphere on the side of the Earth that faces the Sun. This forms a magnetotail on the night side. The stronger the solar wind, the more an aurora oval will stretch.

Did you know?

Solar winds cause the particles to hit Earth’s upper atmosphere at more than 72 million kilometres per hour.

Sometimes, the solar winds can be so strong that they make the magnetic field lines stretch and snap back on the other side of the globe. Like snapping an elastic band, this sends lots of energy to Earth’s poles. This phenomenon, called magnetic reconnection, creates some spectacular auroras! Solar Storms can also cause bursts of auroras.

Solar winds and solar storms cause auroras by starting geomagnetic storms and substorms in Earth’s magnetosphere. Scientists can predict these storms like they predict the weather on Earth. They measure disturbances in the magnetosphere using a scale they call the planetary K index, or Kp. The Kp scale goes from 0 to 9. A forecast below 5 Kp means auroras are not very likely. But a forecast of 8 or 9 Kp could mean a spectacular light show is on the way. 

Incredible KP9 Aurora Borealis Capture By Sony FX3 in Calgary Canada (0:29) from 卡尔加里摄影师Rex

Do auroras make a sound?

In the Sámi language, one of the names for aurora borealis translates as “the light you can hear.” The Sámi language is spoken in Indigenous communities in northern parts of Finland, Sweden, Norway and Russia.

In the 1930s, people in northern Scotland wrote to a local newspaper to report that the aurora made a sound like rusting silk. Many other people and communities have reported that an aurora makes sizzling or popping noises.

Scientists were skeptical about these reports for a long time. Because auroras happen so far above Earth, people on the ground should not be able to hear them. But in 2001, scientists recorded sounds during auroras in eastern Finland. They are still working to record and understand auroral sounds, but they think that they are caused by changes in static electricity in our atmosphere. These changes happen because of the disturbances in Earth’s magnetosphere during auroras. Listen to one of the first recordings of auroral sounds below.

(Audio file courtesy Unto K. Laine (Prof. Emeritus), Aalto University)

Auroras: A Source of Fascination

Humans have been fascinated by auroras for as long as we’ve been able to see them. So it’s not surprising that people around the world have been sharing information about them for a long time, in many different ways.

One of the first written accounts of the auroras was by Assyrian astronomers around 679-655 B.C. But it wasn’t until 1619 that the lights got the name aurora borealis. Italian astronomer Galileo Galilei named them after Aurora, goddess of dawn, and Boreas, god of the north wind in Greco-Roman mythology. Here are a few of the ways Indigenous people in Canada have experienced and learned about the northern lights. Norwegian scientist Kristian Birkeland was the first person to theorize that auroras were caused by solar storms.

Scientists still don’t know everything about auroras, even though they have studied Earth’s magnetic field and solar winds. They still don’t know exactly where the colourful reactions happen. One way they thought they could find out was through the use of satellites.

In 2007, NASA launched five small satellites as part of the THEMIS mission. Each satellite carried an array of electric, magnetic, and particle detectors. Every four days they lined up along Earth’s magnetic tail and tracked disturbances in the magnetosphere. Scientists compared this information to millions of photographs taken at the same time from observatories on the ground. Some of the satellites are still up there, collecting more information.

Image - Text Version

Shown is a colour illustration of the five satellites of the THEMIS mission. Earth’s surface forms a diagonal horizon from the lower left to the top right corner of the image. Cloud cover is visible across most of this. Beyond, space is shown as black. The largest satellite is on the right. At its centre is a silver coloured cylinder with sections of different widths and a cone on one end. Four metal shapes that look like wagon wheels are connected around its sides. Three black and gold, diamond-shaped boxes are attached to these. Two at the bottom and one at the top. The other satellites consist of only the black and gold boxes.

Auroras certainly are a spectacular light show!