Northern Lights Explained: Short and Sweet
The sun emits solar particles into space. Earth receives these particles, and they react with our atmosphere. This reaction between the solar particles and our atmosphere produces the beautiful colors in the sky that we call Aurora.
For those who prefer a more detailed explanation...
Did you know that the Northern Lights are created by our sun?
The Northern Lights, also known as 'Aurora borealis' (Aurora meaning dawn in Latin, and boreal meaning north in Greek), is a display of colorful lights in the sky caused by the interaction between solar winds and Earth's magnetic field.
Solar winds occur when our sun expels its plasma into our solar system. The speed of the particles ejected by the sun depends on its level of activity. During periods of hyperactivity, it's referred to as a solar storm. Approximately every 11 years, the sun goes through a cycle of low and high activity.
The next peak in solar activity is expected between 2023 and 2026.
Auroras form when charged particles from solar winds collide with Earth's magnetic field. They are then trapped and directed toward the magnetic poles, where they enter Earth's atmosphere.
When sun particles collide with Earth's magnetic field, it marks a significant cosmic event.
Earth's magnetic field acts as a protective shield, guarding our planet against solar radiation and preventing atmospheric depletion. However, during periods of heightened solar activity, solar particles can breach our magnetic defences.
At the core of our planet lies a sphere of iron, equivalent in size to our moon.
Earth operates as an immense magnet, with its magnetic field resulting from a combination of factors: Earth's rotation (spinning), the presence of iron in the core (conductivity), and droplets of molten iron that freeze and solidify on Earth's inner core. Under pressure, warm liquids spiral upward, while cooler solids spiral downward (convection).
Earth possesses a metallic iron core, often referred to as the magnetic core. This core operates much like a bar magnet, complete with two poles and an encompassing magnetic field.
Strong solar winds can propel charged solar particles, comprising electrons and protons, at staggering speeds of up to 900 km/s through our solar system, at temperatures soaring to 1 million degrees Celsius.
When these electrons encounter our magnetic field, some become ensnared within the Van Allen radiation belt, while others navigate the magnetic grid, eventually being drawn through the magnetic poles and into the atmosphere.
As these electrons cascade into the atmosphere, they impart energy to the oxygen and nitrogen atoms in our atmosphere. When an atom receives this surge of energy, it becomes "excited," signifying that one or more of its electrons have transitioned into higher state orbitals. To return to its normal state, the atom must release this excess energy. It accomplishes this by spontaneously creating a photon out of the vacuum! (I'm still wrapping my head around that one.)
The emission of a photon is what we perceive as light. The Northern Lights are the result of photons being released in the atmosphere by either nitrogen or oxygen atoms.
Aurora light is considerably dimmer than sunlight, which is why we can only appreciate this phenomenon after sundown.
But why do the Northern Lights come in different colors?
These lights manifest in Earth's atmosphere and exhibit various hues. While green is the most common, they can also appear in yellow, red, violet, and blue.
Our atmosphere is approximately 1000 kilometers thick (although data on this varies greatly) and is primarily composed of nitrogen and oxygen. The hue of the Aurora depends on the atmospheric depth at which the 'solar' electron energizes the oxygen or nitrogen atom.
Red lights are generated by atomic oxygen situated above 200 kilometers. At this altitude, oxygen atoms are widely spaced, allowing ample time for them to emit red photons before another atom collides with them and absorbs that energy. The green photons, emitted by oxygen atoms, are the most prevalent and frequently observed in Auroras because they are generated in three-quarters of a second—much quicker than the red photons, which take two minutes to be emitted.
To witness the violet auroras produced by low-altitude atomic nitrogen, you'll need strong solar activity, as it demands auroral electrons with enough energy to give them the impetus to penetrate deeper into the atmosphere, reaching the lower-altitude nitrogen.
The colors of the Aurora are contingent on the altitude at which the charged electron penetrates our atmosphere and which type of atom it 'excites': nitrogen or oxygen.
The image above provides an illustration of the Aurora color you can expect to see based on altitude.
Atomic oxygen is predominantly found above 100 kilometers, while atomic nitrogen is more prevalent below 80 kilometers, where atomic oxygen is essentially absent. (The air we breathe consists of molecular oxygen.)
Above 80 kilometers, the majority of light emissions (photons) are produced by 'excited' oxygen atoms.
Where Can You See the Northern Lights?
The prime location for viewing the Aurora borealis is along the Arctic Circle. As solar particles are captured in our magnetic field, they enter the atmosphere at both the south and north magnetic poles. Countries situated along the Arctic Circle include Iceland, Finland, Norway, Sweden, Greenland, Canada, the U.S. (Alaska), and Russia.
Countries like Iceland, Norway, Finland, and Sweden offer a plethora of guided tours to assist you in locating the Northern Lights, though successful viewing will primarily hinge on solar activity and sky clarity.
Map dated 1906, showing the Arctic Circle where Aurora Borealis can be viewed.
What are the Best Months to See the Northern Lights?
The phenomenon of the Aurora is constant, but its light is much fainter compared to the sun. Therefore, you'll need total darkness to fully appreciate it.
To maximize your chances of witnessing the Northern Lights, it's essential to travel to the Arctic Circle during the period when days are short and nights are long. Additionally, you'll want to ensure there's minimal cloud cover.
From September to February, you'll benefit from the advantage of long nights. However, it's important to note that the weather can be unpredictable. The best advice is to allocate yourself a couple of weeks on-site to increase your chances of catching a glimpse of the Aurora.