The Light at the End of the Collision
The Northern Lights explained
If you’re lucky enough to live near or visit places like Alaska, northwestern Canada, the northern coast of Norway, or Iceland, you may have seen the colorful dancing lights in the sky — a beautiful array of colors and patterns that brings awe and wonder to those who experience them. These are known as the Aurora Borealis.
More commonly, this phenomenon is referred to as the Northern Lights. But in fact, it’s not a phenomenon at all. The light display is caused by charged particles from the sun that interact with the Earth’s magnetic field.
That magnetic field acts as an invisible shield over our planet, with lines extending from north to south poles. It protects us from the many particles that come from the sun, especially those that can be released by occasional large flares of the sun. On the sun, 93 million miles away, the temperature is so incredibly hot that gas molecule collisions happen quite frequently. These collisions result in free protons and electrons being shot out of the sun’s atmosphere and pushed towards the Earth on solar winds.
Many of these particles are deflected by the magnetic field, but at the poles, the field is weaker. As a particle approaches the poles, it moves along the magnetic field lines in a spiral and eventually breaks into the atmosphere, where it will collide with gaseous particles like oxygen and nitrogen. This collision creates photons of light, which are what we see in the aurora.
The Northern Lights are most often a pale green or pink, but they’re able to take on many colors based on what gases they collide with. A collision with an oxygen molecule at a lower altitude of about 60 miles above the earth leads to pale yellow-green colors, while a collision with that same molecule at a much higher altitude of 200 miles will bring about rare red colors. Collisions with nitrogen cause blue and purple-red colors.
The light displays that these particle collisions create extend between 50 and 400 miles above the earth’s surface and present themselves in many forms — from patches to streamers, scattered clouds of light, and light curtains. While they are more often seen around the northern pole, the Aurora Australis (Southern Lights) occurs at the south pole, under the same principles. The auroras across the world from each other mirror each other, occurring at the same time and showing the same colors. Unfortunately, the Southern Lights present in a ring around Antarctica and over the Indian ocean and are therefore harder to see.
If you’re looking to find yourself some ripples of color across the night sky, your best opportunities will be to travel up north over the winter in areas without light pollution. Around midnight, take a look up at the sky and you may be able to see, and even sometimes hear, tiny particles colliding and colorful photons. Auroras work cyclically, peaking every 11 years, so your best chance to see the brightest display won’t be coming until 2024.
