Wednesday, July 28, 2021

What are Red sprites?

Lightnings are atmospheric phenomena that we all have in mind. However, they are not the only phenomena related to electrostatic electricity that occur in the Earth's atmosphere.

Associated with thunderstorms it is sometimes possible to observe red sprites, such as those shown in the image. Unlike normal lightning, these are much rarer and much more difficult to see with the naked eye, since their duration is only a few milliseconds.

Sprites aren’t terribly well known, except to meteorologists, nature photographers and others who study the skies. They aren’t especially rare, but they’re fleeting. They’re not easy to capture on film.

 Lightning sprites are electrical discharges high in Earth’s atmosphere. They’re associated with thunderstorms, but they’re not born in the same clouds that send us rain. Thunderstorms – in fact all earthly weather – happen in the layer of Earth’s atmosphere called the troposphere, which extends from Earth’s surface to about 4 to 12 miles (about 6 to 19 km) up. Lightning sprites – also known as red sprites – happen in Earth’s mesosphere, up to 50 miles (80 km) high in the sky.

Their red color is instead due to nitrogen, the main element that makes up the Earth's atmosphere.

To photograph a sprite, you need a dark sky and a clear view toward a distant thunderstorm. The sky needs to be dark, because you’ll be taking long exposures; too much stray light in your sky will wash out your photo and make capturing sprites impossible. 

Credit: Yuri Beletsky (Carnegie Las Campanas Observatory, TWAN).

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