Had I not been so focused on observing a gas cloud 4,000 light years away I might have seen my first sprite last night. Sprites are massive electrical discharges that occur high above thunderstorms. They look like jellyfish tentacles. Unlike lightning, which at 10,000° F is as hot as the face of the sun, sprites are cool, more like the cold glow of a fluorescent light. Individual sprites in a cluster span between 33 to 328 feet (10 to 100 m) across and flash into view from 31 and 60 miles (19 and 37 km) high, far above the tops of thunderclouds in a layer of the atmosphere called the ionosphere, the same region that hosts the aurora.
Red sprite bursts by Scott McPartland
Sprites are only faintly visible with the naked eye from a dark sky, appear colorless and flash into view for a split second. Thanks to a camera’s greater sensitivity they glow red in time exposures like what you see in Jim’s photo. A line of thunderstorms passed through the area last night that continued to produce lightning long after departing. I was a different mission last night and delayed my sprite-watching until after midnight and tried to see them by eye only. Stars studded the sky and lightning flashes were nearly continuous from a different storm some 150 miles away, so far no clouds were visible even at the horizon. Many people call this heat-lightning — lightning without the thunder. But it’s just normal lightning only from a storm so far away you can’t hear it.
Red sprites are produced by positive lighting, not the far more common negative variety. In a thunderhead, colliding ice particles whipped around by powerful updrafts can be stripped of electrons and become positively charged or gain electrons and become negatively charged. The positive charges generally rise to the top of the cloud, while the negatives collect in the cloud’s base.
As the charges build in intensity, positive and negative desperately seek each other out. Eventually, the difference in charges is enough to overcome air resistance, and the two connect and discharge in a bolt of lightning. During most storms, the flow of electricity is from the negatively charged cloud bottom to the positively-charged top or down to the positively charged ground, called negative lightning. Only 5% of lightning runs the other way from positive to negative, what meteorologists call positive lightning. It occurs during the peak and decaying stages of a massive thunderstorm, when a positive strike exits from the top of a thundercloud, sidesteps the cloud bottom and directly strikes a patch of negatively charged ground.
Positive lighting is five times hotter and more powerful than the negative version, lasts longer and can strike from a distance of several miles—the classic “bolt from the blue.” It’s also the trigger for red sprites
While I saw lots of flickering I went home spriteless. So I’d like to remind you to look for this strange electrical phenomenon only recently recognized. You can try to sight one by eye, but you’re better off with a good digital camera — a Canon Rebel would do the job. When a distant storm flashes and flares along the horizon or just beyond, and the night sky is clear without moonlight, that’s the time to capture a sprite. The best sprite viewing occurs when thunderstorms are located between 100 and 200 miles (160 and 480 km) away. Check National Weather Service radar maps for thunderstorm activity in your
region at weather.gov/Radar.
Place your camera on a tripod, set everything to manual (M) and focus manually on a bright star. Use a wide angle lens (16mm, 24mm, 35mm), open the lens to its widest setting (f/2.8, f/3.5 or f/4) to let in the maximum amount of light and dial up your ISO to 3200 or 6400. You need sensitivity (a high ISO) because sprites are brief and generally faint. Then start taking time exposures — anywhere from 15 to 30 seconds. One after another after another. Check the back screen once in a while to see if you snagged one.
May a thunderstorm head your way soon!