Red Sprites
Some phenomena in the sky are so brief and strange that, while some spend decades looking for proof, others confuse them with UFOs. Today, let’s talk about one of these phenomena (not UFOs. However....)
Children of storms
It all starts with lightning. As you remember, lightning is an exchange of particles among clouds or between a cloud and the earth. The particles participating in the exchange have a unique property: they are charged.
Negatively charged particles, electrons, are attracted to positively charged protons. Lightning happens because of this mutual attraction: if there are too many electrons in the cloud, they begin to «feel» where to find a large concentration of protons on the ground (in a lightning rod, for example).
Red sprites taking the shape of carrot roots. Photo: Nicolas Escurat
In reality, of course, the particles do not feel anything; they just obey the laws of physics, which force them to move towards each other. As soon as there is a successful «string» of particles in the air between the cloud and something on the ground that are close enough; the cloud throws an avalanche of electrons along this string.
Electrons are the particles that move to create lightning, because they are much lighter than protons that attract them. And they fly at such a furious speed that, crashing into air particles on their way to the ground, they emit light by making the air around them glow. That’s why we see lightning as a blindingly bright flash.
But other things are also happening. Occasionally, there are so many electrons in a place on the ground (for instance, in moist soil or metal objects) that the electrons move toward the cloud from the ground instead of the other way around. This rare discharge is called positive lightning.
Since any lightning is an exchange of charges, positive lightning leaves the cloud with a strong negative charge—a large number of electrons. And those electrons want to reach for the protons again. But if there aren’t enough of them down below, they have to reach in another direction: up.
There, at altitudes of up to 90 kilometers, particles from space, including those from the surface of the Sun, collide with air particles, and leave them mostly with a positive charge: a suitable target for our electrons, which immediately, in a split second after positive lightning, fly upwards.
This weak discharge from the thundercloud almost into space is called a red sprite.
Why red
Sprites were first photographed only in 1989. And it’s not because they’re incredibly rare. It’s just that they only last for thousandths of a second, so cameras need to be very fast.
Because of the elusiveness of sprites, they received this name, because Sprite is not only a drink, but also a spirit, a fairy or an elf. Sprites look different—there are sprites in the shapes of jellyfish, columns, or even carrots.
Sprites in the form of jellyfish. Photo: Paul Smith
Red sprites are made of nitrogen. At an altitude of 50-90 kilometers, where sprites live, electrons mainly encounter nitrogen atoms—these receive the energy.
Nitrogen also has its own electrons, which «absorb» the collision’s force, and then return to their normal state, dumping the excess energy in the form of particles of light. The energy of light particles, that is, their color, depends on the size of the atom. And it just so happens that the red particles are spit out by nitrogen; hence, the red sprites.
Sprites are not called lightning because these phenomena have incredibly different temperatures. Sprites are much closer to the discharges inside daylight bulbs: both have low gas pressure and are quite cold, at or below room temperature. Lightning, on the other hand, can heat the air to 30,000 degrees Celsius, which is almost 6 times hotter than the surface of the Sun!
Where to catch these sprites
Sprites can be found over powerful thunderstorms in temperate and tropical latitudes. The bad news is that you’ll need a camera capable of taking at least a thousand frames per second—the phenomenon is easy to miss.
But there is good news—sprites are huge, they can take up to 50 kilometers in length and width, which means the lens will surely capture them. It’s best to observe them at night, in places with minimal light pollution. The naked eye can see them, but because of the short duration of the phenomenon it is extremely difficult.
Sprites in the form of columns. The phenomenon occurs so high up, that the storm cloud in the photo is often hidden behind the horizon. Photo: Oscar Van Der Velde
Sprites have been photographed literally thousands of times since 1989, so the odds are good. There are even places where the phenomenon is noticed most often: hunters for sprites are advised to look for them over the Great Plains in the United States and Canada.
But any country with frequent thunderstorms, like Thailand and Argentina, can be suitable. Often sprites are accompanied by rare phenomena of other colors, which we will definitely tell you about in future articles.
Text: Jason Bright, a journalist, and a traveler
Cover photo: Nicolas Escurat / astrobin.com
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