What is the Aurora? Answering questions about this astronomical phenomenon!

The weekend of May 10-11, the Aurora Borealis, also known as the Northern Lights, swept the skies of Canada, the United States, and many other places around the world. If you were able to see the show, great! It was one of the best displays of auroras in 20 years! Photos of this gorgeous light show have been circulating the internet in the past few days, and we're here to answer your questions about this phenomenon.

The auroras were a lot brighter and colourful in pictures. To the eye, the display was fainter and colours less obvious. Still, it was an amazing show! Credit: Julie Bolduc-Duval.

What causes the aurora?

Our Sun is a star, which means it's made up of extremely hot gas. When is it very active, it can eject matter into space which can reach Earth. This matter is mostly made up of charged particles (electrons, protons, ions) which are deflected by our magnetic field. They can enter the atmosphere around the polar regions, and they interact with the atoms in our atmosphere. This causes the emission of light of different colours: the aurora!

The lights also appear to move; sometimes slowly and sometimes quite fast. Check out this amazing time-lapse from Canadian astrophotographer Alan Dyer.

What is the difference between auroras and northern lights?

There’s no difference! When the aurora happens in the northern hemisphere of Earth, it's called aurora borealis or the northern lights. When the aurora happens in the southern hemisphere of the Earth, it's called the aurora australis or the southern lights.

Why were there auroras now? 

Since the auroras are caused by the Sun’s ejected material interacting with atoms in Earth’s atmosphere, the aurora happens when the Sun is more active and ejects more material. 

The Sun becomes more active and ejects more material on a cycle, every 11 years. Right now, the Sun is in an active period and is expected to be increasingly active until mid-2025, after which the Sun will become less active and reach a low point in activity by the late 2020s.

The auroras on May 10-11 were caused by a solar storm –a large solar ejection– that made its way towards Earth. While this sounds scary, the material from the Sun was dispersed in the atmosphere widely from the poles, causing the beautiful aurora light show.

Why were we able to see the northern lights so far south in Canada and the US?

Since the Sun is at a point of high activity in its 11-year activity cycle, it is ejecting more material than it has in the last decade! As the particles interact with the Earth’s magnetic field, they are distributed towards the poles of the planet and then interact with the atoms in the atmosphere, releasing energy as light that is visible in a ring of latitudes around the poles. This ring of latitudes is called the auroral oval. Usually, this auroral oval stays fairly far north (or south, in the southern hemisphere), but when a solar storm happens, this oval can go to lower latitudes.  The aurora on May 10 was seen all the way to Mexico and Hawaii!!

Auroral oval on a regular day, and on May 10. Credit: NOAA Space Weather Prediction Center

Will there be more auroras?

Most likely! We can expect more auroras in the coming months as we reach the solar maximum (time of highest solar activity within its 11-year cycle). However, it’s impossible to predict long in advance and how intense they will be. When we see a solar storm, we know the chances of auroras are higher in the coming days, when the particles reach the Earth (it only takes light from the Sun 8 minutes to reach us, but it's much longer for particles).  

Big sunspots on the Sun are an indication of more solar activity. They appear darker on the surface of the Sun since they are less hot. Large ones such as the one labelled 3664 in this image can be seen with eclipse glasses. If you look at the Sun regularly (in the sky with your eclipse glasses, or online such as on SpaceWeather.com), you might see sunspots and know when the chances of auroras are higher! 

The Sun on May 10, 2024, with sunspot group 3664, responsible for the ejection which created the aurora. Credit: Solar Dynamics Observatory. 

Why are there different colours?

Aurora can be very colourful! The colours are determined by multiple factors, mostly the composition of gases in Earth's atmosphere and the altitude where the aurora occurs. Different gases in the atmosphere (oxygen, nitrogen, etc.) will create different colours at different altitudes. For more details, check out this page by the Canadian Space Agency. 

When the aurora isn’t very strong, it will mostly appear white. Green is the most common colour. On May 10, we were treated to an amazing show with many colours: green, red, pink and even purple! 

Why were the colours more obvious on a camera?

Simply, it is because the sensors of the camera are much more sensitive than our eyes! Furthermore, we can do long exposures with the camera, which we can’t do with our eyes. Recent cell phones automatically take exposures of a few seconds in night mode. The pictures shown below were taken with an iPhone in night mode, which took exposures of 3 seconds. 

Below are some photos taken on May 10, 2024 of the aurora.

Credit: Julie Bolduc-Duval

Teaching Opportunity

With such a beautiful astronomical phenomenon gracing our skies the weekend of May 10, it poses another unique teaching and learning opportunity. Below are some activities you can use to discuss the aurora borealis in your classroom and connect it to the Sun and the rest of our Solar System.

• Investigating the Solar Cycle

  • Since the aurora is dependent on the Sun’s activity, it’s only natural to explore the Solar Cycle when talking about auroras.  Our Solar Cycle activity guide is aimed towards secondary school teachers to help students investigate the solar cycle. Using real satellite images of the Sun, six (6) activities are investigated in this guide, covering topics such as the differences between astronomical observations at multiple wavelengths, terrestrial phenomena related to solar activity, and more.

• Creating a Scale Model of the Solar System

  • The scale of the distances in the Solar System are something that can be discussed when talking about the aurora. Since the ejected particles from the Sun have to travel all the way to Earth, creating your very own scale model of this would help visualize that distance. Our Solar System interactive activity allows you to create models of the Solar System with your students.

• Night Sky Observation 

  • The beautiful phenomenon of the aurora on May 10 caused everyone to look up to the sky. And while the aurora isn’t always visible, there is so much more to see up there too! We offer several activities to encourage observing the night sky. 

  • Our Looking Up Activities are designed to help students know what is visible in the night sky and provide a template for documenting their observations.

• Making your own aurora!

  • Connecting to astronomy through arts and crafts is a great way to engage students. There are so many ways to make your own aurora, but here are some ideas to do this:

    • Use green, pink, and white pastels and/or chalk and smudging the pigment across a sheet of black paper.

    • Take a long exposure photo while moving glow sticks. Here is a guide to taking long exposure photos on a smartphone.