Last week the sky came out to play, and I crossed off a bucket list item that had begun to feel like a cosmic joke. Now I can say that I have seen an aurora from my front door.
In the Noughties, I went to Iceland and Scandinavia in the hope of seeing the Northern Lights, with no luck. Lovely places, but it was a quiet time for the Sun. Last week in Portloaise, my luck came in.

Even better, last week’s unlikely to be my last chance. We are heading towards the peak of Solar Cycle 25, with the 11-year cycle of solar activity due to reach its maximum in July next year when the Sun’s magnetic poles reverse. As the cycle intensifies, sunspots gather on the face of our star as its magnetic fields write, intermittently throwing off balls of plasma towards the planets.
Most of these eruptions miss the Earth, but a few hit the natural magnetic shield that protects our bubble of life. The plasma is accelerated by the magnetosphere, diverting its energy away from the Earth’s surface towards the north and south poles. It collides with particles in the upper atmosphere, energising them to set off waves of green, red, blue and yellow — a natural version of neon lights. These colours tell a story.
Secrets tales of the aurora

Charged particles in the Northern Lights (aurora borealis) and Southern Lights (aurora australis) reveal the Earth’s magnetic field. This hidden shell keeps solar radiation from sterilising our home as it did on Mars.
When particles hit atoms and molecules of gas in our outer atmosphere, they gain energy and release it as light. The colour of the light reveals how much energy was lost, and what sort of gas it came from.
The ionosphere, between 100 and 400 kilometres, is mostly nitrogen and oxygen, with a little neon, helium, argon and hydrogen. Oxygen molecules (O2) don’t light up for aurorae, but atomic oxygen is much easier to excite. It’s responsible for both red and green aurorae, at different altitudes.
Blue and violet at the top of the aurora are faint and rarely seen without dark skies. They come from hydrogen and helium on the edge of the atmosphere at 300-400 km. Red lights arise at the same altitude but require less energy. These high-up lights are more visible at low latitudes like central Ireland.
Green will be seen
Green aurorae at at the lower altitudes of 100-300 km are the most common. That’s because we see green better and the air is thicker here, so there’s more to excite. If you see green at low latitudes as we did last week, it’s a sign of an intense solar storm. It’s an indirect colour, given off when excited oxygen atoms collide with excited nitrogen molecules (N2+). Those excited nitrogen molecules also produce blue and blue-green lights at the same altitude.
Lower altitude lights at the base of the aurora, around 100 km up, are very rarely seen at low latitudes. They also come from excited nitrogen molecules. Deep red comes from their interaction with atomic oxygen, but it can overlap with other colours to produce purple, pink and orange hues. Energetic blue-violet is the pure light from excited nitrogen molecules that haven’t interacted with oxygen.

Did you see STEVE, aurora’s hot friend?
Some of the Northern Lights seen last week weren’t aurorae, but a friend called Steve. Steve sometimes appears, as a purple or green ribbon light, with an aurora. It wasn’t identified until a few years ago, and stands for Strong Thermal Emission Velocity Enhancement (a backronym with its own story).
A Steve can last for up to an hour and is thought to be a stream of ionised particles. Scientists have yet to decide how and why they form, or what role they play in routing the energy of solar storms through our atmosphere.
An otherworldy aurora

Aurorae can happen on any planet that has a magnetic field. Of the inner four planets around the Sun, only the Earth has a significant magnetic presence.
Future Mars colonists will need advance warning to reach protection before a solar storm hits their world. Anyone foolish enough to stay outside would see a kind of aurora on the day side of Mars — the red glow of oxygen atoms hit by incoming particles. They’d also be watching a process which is slowly stripping Mars of its atmosphere and taking away vital oxygen.
Venus also shows flashes of visible and ultraviolet light when solar storms hit its atmosphere. In this case, it’s already lethally thick and toxic to life. Solar storms would be a low priority problem.
We really do live in the Goldilocks zone.
Gas giants’ DIY auroas
The gas giants — Jupiter, Saturn, Uranus and Neptune — all have intense magnetic fields that produce aurorae. Jupiter’s spectacular lights are made by particles so energetic that they would kill anyone on its inner moons. It collects particles from the atmospheres and volcanoes of those moons, and lights up even when there are no solar storms.
Saturn’s polar aurorae are mostly ultraviolet, and are thought to be produced by both solar storms and particles harvested from its own moons. They feature in my forthcoming SF series1Forthcoming in the sense that I really need to complete the second and third books because I want to publish them as a set. File under 2025., In Machina, because I love background details that bring a location alive.
Little is known about the ultraviolet aurorae of Uranus and Neptune, except that they exist and they’re bound to be very strange. Both planets have magnetic fields tilted heavily from their equators. Neptune also rotates almost 90 degrees to the ecliptic, so that one pole faces the Sun, adding to its weird quotient.
There’s no doubt that planets around other stars with have strange and marvellous aurorae. Just perhaps, a sapiophile alien author on a distant planet is qlogging about their delight in finally seeing the lights in their sky.
All images author’s own. All rights reserved.