Journal Information
Universe:
Cosmos
Focus:
Northern Lights, Solar Wind, Earth’s Magnetic Field, Atmosphere, Colour and Cosmic Visual Language
Reading Time:
12 Minutes
" When we see layers of green, red or purple light slowly curling across a dark sky, the display can feel as though it is happening somewhere far beyond Earth’s atmosphere. In reality, the Northern Lights are one of the clearest examples of the relationship between the Sun and Earth becoming visible within our own atmosphere. Charged particles from the Sun interact with Earth’s magnetic environment, are guided towards the polar regions and can produce light when they encounter atoms and molecules in the atmosphere. The colours, shapes and movements in the sky constantly change throughout this process. The Northern Lights, also known as the aurora borealis, are therefore not simply a beautiful sight in the sky, but a physical interaction that begins at the Sun and becomes visible in Earth’s upper atmosphere."
What Causes the Northern Lights?
What Are the Northern Lights?
The Northern Lights are a natural atmospheric light phenomenon seen around Earth’s northern polar regions. Scientifically known as the aurora borealis, they can appear as thin arcs, broad bands of light, curtain-like folds or more diffuse glows across the sky. Some auroras remain relatively calm for long periods, while others can change shape rapidly within minutes and produce an intensely dynamic display.
When the same physical process occurs in the Southern Hemisphere, it is known as the aurora australis, or Southern Lights. Both types of aurora result from the same fundamental mechanism. The difference lies in which polar region of Earth they appear around. Rather than thinking of the Northern Lights as an atmospheric event belonging only to northern countries, it is more accurate to see them as part of a larger system produced by Earth’s magnetic structure around both poles.
Auroras form far above the atmospheric layers where most everyday weather takes place. Clouds, rain and wind occur mainly in the lower parts of the atmosphere, while auroras usually appear much higher, tens or even hundreds of kilometres above the surface. They may look like coloured light passing behind clouds, but physically they occur in a very different region of the atmosphere.
The Northern Lights are also not simply glowing curtains suspended in space. The light appears when atoms and molecules in the atmosphere gain energy and later release some of that energy as light. The energy involved is largely connected with charged particles arriving from the Sun.
To understand an aurora, we therefore need to look not only at Earth’s atmosphere, but also at the Sun, around 150 million kilometres away.
The story of the light we see does not begin in our sky.
The physical journey of the Northern Lights begins at the Sun and becomes visible in Earth’s upper atmosphere.
How Does the Sun Produce the Northern Lights?
The Sun sends us more than light and heat. It also continuously releases a stream of protons, electrons and other charged particles into space. This flow of particles is known as the solar wind, and it travels throughout the Solar System.
Earth does not sit completely unprotected within this flow. Our planet has its own magnetic field, which extends into space and forms a large magnetic region known as the magnetosphere. When the solar wind reaches Earth, it encounters the magnetosphere, which deflects a large proportion of the incoming particles around the planet.
The system, however, is not a completely closed shield. Under certain conditions, the magnetic field carried by the solar wind can interact with Earth’s magnetic field and allow energy to enter the magnetosphere. As a result, some charged particles can be accelerated along Earth’s magnetic field lines towards the polar regions.
Earth’s magnetic field therefore plays an important guiding role. Because magnetic field lines converge towards the atmosphere around the poles, many of these charged particles are directed into the upper atmosphere near the northern and southern polar regions. This is why auroras do not appear equally across the entire planet, but are seen more often within ring-shaped regions around the poles.
When charged particles encounter oxygen and nitrogen atoms and molecules in the upper atmosphere, they can transfer energy to them. These energised atoms and molecules later return to lower-energy states and release light at particular wavelengths. The green, red, blue or purple light that reaches our eyes originates in these energy transitions.
At times, stronger activity on the Sun can significantly affect this system around Earth. For example, a coronal mass ejection, in which large amounts of plasma are thrown into space from the Sun, can cause major changes in the magnetosphere if it travels towards Earth. When the speed and magnetic conditions of the solar wind are favourable, more intense magnetic activity known as a geomagnetic storm can develop around our planet.
During such periods, auroras can become brighter and may extend farther south than the polar regions where they are normally seen.
It is important to understand that an aurora is not coloured light travelling directly from the Sun to Earth. The Sun provides the particles carrying energy and the magnetic conditions that drive the process. The visible light itself is produced when that energy interacts with matter in Earth’s atmosphere.
In other words, the Northern Lights are an image shaped by two worlds.
The Sun supplies the energy.
Earth’s magnetic field shapes the movement of the particles.
The atmosphere turns that interaction into visible light.
An aurora is the visible expression in our sky of an otherwise invisible physical relationship between the Sun and Earth.
Why Can the Northern Lights Appear Green, Red, Purple or Blue?
Green is the colour most strongly associated with the Northern Lights. Auroras, however, are not only green. Red, purple, pink and bluish tones can also appear, and during some strong displays several colours may be visible in the sky at the same time.
The main reason for these colours is that different atoms and molecules in the atmosphere emit light at different wavelengths when they are excited at different energy levels. Oxygen and nitrogen in particular play major roles in auroral colour. The type of gas involved, the amount of energy carried by the particles and the altitude at which the interaction occurs can all affect the colour that reaches our eyes.
Green aurora is largely associated with atomic oxygen and is often one of the easiest colours to recognise in auroral displays. The human eye is also relatively sensitive to green light, which helps make this colour especially noticeable. Someone observing an aurora with the naked eye may therefore see a paler green than a camera records, or may notice only a greyish glow when the aurora is weak.
Red aurora can also be associated with oxygen, but it usually occurs at higher altitudes and under different energy conditions. At greater heights, the atmosphere is much thinner and collisions between atoms happen less frequently. These conditions can allow oxygen to emit red light through a different energy transition.
Nitrogen can contribute more strongly to blue and purple tones. Interactions between energetic particles and nitrogen molecules or ions can help produce purplish, bluish or pink colours, particularly along the lower edges of auroral forms. It is therefore possible for the upper part of an auroral curtain to appear red, the middle to glow green and the lower edge to take on a purple tone.
The mixing of colours can make the aurora even more complex. Different gases can emit light at several altitudes at the same time, allowing colours to overlap in the light that reaches us. Camera sensors can also collect light for longer than the human eye, which means aurora photographs may show colours much more strongly than they appeared to someone standing beneath the same sky.
This creates a natural connection with the question we previously explored in Are the Colours We See in Space Images Real? The two subjects, however, are not the same. In deep-space imagery, data recorded at different wavelengths may be represented visually, while during an aurora, visible light is genuinely being produced within the atmosphere.
Camera settings, exposure time and image processing can still influence how intense those colours appear in a photograph.
A highly saturated green or purple aurora image seen online does not therefore mean that the human eye experienced exactly the same level of colour intensity at the time. But neither does that mean the colours themselves are physically unreal.
Auroral colour carries information about which part of the atmosphere is being energised and under what conditions.
The colour in the sky is not merely a visual detail, but the visible result of physical interactions taking place within the atmosphere.
Why Can the Northern Lights Sometimes Be Seen from the UK?
When people think of the Northern Lights, places such as Norway, Iceland, Finland or northern Canada often come to mind first. This is because auroras are most frequently seen in regions surrounding Earth’s magnetic poles. Together, these regions form a ring-shaped area commonly known as the auroral oval.
The oval is not a fixed boundary. As the strength of the solar wind and conditions within Earth’s magnetosphere change, the area where auroras can be seen can expand or contract. During quieter space-weather conditions, strong aurora generally remains farther north. During intense geomagnetic activity, however, the auroral oval can expand towards lower latitudes.
The UK is therefore not a place where auroras can be seen every night, but neither is it completely outside the region in which they can occur. Northern parts of Scotland are at higher latitudes and are therefore much better placed than southern England. Northern England and other regions can also see aurora when geomagnetic conditions are sufficiently strong.
During particularly intense geomagnetic storms, the visible auroral region can expand even farther south. Under such conditions, coloured glows may sometimes be visible towards the northern horizon from central or southern parts of England. Historical observations also show that exceptionally strong events can bring aurora to latitudes much lower than their usual viewing regions.
Suitable space-weather conditions alone, however, are not enough. Observing conditions on Earth must also be favourable. Cloud can completely obscure the light occurring in the upper atmosphere, city lighting can make a weak aurora difficult to notice and bright moonlight can reduce contrast.
For aurora viewing in the UK, a clear northern horizon, a dark location and a sky with as little cloud as possible are therefore important. Even when geomagnetic activity is strong, aurora can be difficult to detect with the naked eye under heavy light pollution.
Cameras can reveal more detail than the human eye in these situations. Long exposures or night modes can make green, red or purple colours much more obvious, even when the aurora appeared only as a faint glow to the observer.
Seeing aurora from the UK does not therefore necessarily mean witnessing dramatic green curtains filling the entire sky. In more southerly regions, an aurora may begin as a faint reddish glow or a subtle area of coloured light near the northern horizon.
The important point is that aurora seen from the UK is not a physically different event.
An aurora visible in Scotland and one seen in Norway arise from the same fundamental process.
The difference is how far south the auroral oval has expanded at that moment and where the observer is positioned in relation to it.
The Northern Lights appearing over the UK can therefore be understood not as a random display of colour in the sky, but as a visible consequence of solar activity changing Earth’s magnetic environment strongly enough to affect a much wider region.
Aurora visible from the UK is one of the clearest signs of how far changes in space weather can extend across Earth.
Why Are the Northern Lights So Powerful in Cosmic Visual Culture?
The visual character of aurora is different from many other cosmic images. A planet has a defined and limited form. A star can appear as an intense point of light. A galaxy or nebula may be associated with a recognisable structure. The Northern Lights, by contrast, are constantly shifting, folding and changing, with no fixed boundary.
The composition is therefore not defined by a single object.
It is defined by movement.
Bands of light can widen, narrow, curve or transform into completely different forms within minutes. An aurora photograph captures not a structure that remains unchanged for long periods, but one moment within a continuous flow.
The contrast between green or red light and the dark sky also plays an important role in the visual power of the display. The negative space surrounding the light makes the aurora more visible and helps communicate the scale of the sky. There is no need to fill every area with stars or other celestial objects.
A single green curtain crossing a broad dark field can carry an entire composition.
Aurora also visually blurs the boundary between Earth and the cosmos. When we look at stars, we are usually observing distant regions of space. With the Northern Lights, energy originating from a cosmic source becomes visible directly within our own atmosphere.
In that sense, aurora is not only an image of space.
It is an image of Earth.
An image of the atmosphere.
And at the same time, an image of the connection between the Sun and our planet.
This makes it a very different visual source within cosmic art and graphic design. Vertical curtains of light can introduce a sense of height, auroral arcs stretching horizontally can carry the eye across a broad composition and curved bands of light can produce natural movement within an image.
Transitions between colours can strengthen that sense of movement. Narrow regions changing from green into purple or red can make the light feel more layered than a single flat tone. Yet a composition inspired by real aurora does not need to contain every possible colour at once.
The real sky often does not either.
Sometimes only green is visible.
Sometimes a faint red.
Sometimes only a very subtle light that a camera can reveal more clearly.
This simplicity does not weaken the effect. On the contrary, a limited area of light within a wide field of darkness can produce a stronger atmosphere.
Perhaps this is one reason the Northern Lights feel so visually striking. The display is physically real, yet it can appear almost unreal. The light is not fixed, but neither is it random. Its form is shaped together by particles from the Sun, Earth’s magnetic field and gases within the atmosphere.
In other words, the curves we see are not merely aesthetic patterns.
There is physics behind them.
There is the Sun.
There is a magnetic field.
There is the atmosphere.
And where all of these meet, there is light.
When we see the Northern Lights above a dark sky, we are not simply looking at a green or red curtain.
We are watching energy that began at the Sun, around 150 million kilometres away, pass through Earth’s magnetic environment and become visible within our atmosphere.
Perhaps that is the most powerful aspect of aurora.
A cosmic event that appears distant is actually taking place within the upper atmosphere of our own planet.
The Northern Lights are the invisible connection between the Sun and Earth becoming visible through colour and movement in the sky.
Continue the Journey
If the contrast between darkness and light is what draws you to the cosmos, continue with Within the Darkness. A radiant white star burns within a dark blue cloud of gas and dust, revealing hidden layers and scattered stars without removing the darkness around them.
Within the Darkness carries the same visual tension explored throughout this Journal into a cosmic graphic composition. The light becomes more visible because of the darkness surrounding it, while a deeper region remains beyond its reach. The design turns darkness from an empty background into an active part of the image, shaping what can be seen and what still remains unknown.
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