How does lightning illuminate the sky?

Submitted by AverageMan282 t3_10exqut in askscience

Last night my family and I were debating how the light moves from the electricity (or plasma, whichever makes the electromagnetic radiation) to our eyes whenever lightning strikes.

I proposed that if the light didn't scatter through the droplets and atmosphere, then all we would see is the strike itself and the sky would remain dark. So I was imagining that refraction between water and air as well as internal reflection of the droplets is what causes the light to reach our eyes, not that the sky lights up like a light bulb does.

I also argued that different points on Earth would receive varying levels of light from each strike because of the random nature of water droplets and the structure they happen to form at that moment. So whether a particular strike is bright depends on where you are, not just the amount of energy released. (because different places would receive different numbers of rays, so the sky looks a different brightness. Kinda like how the moon always reflects along a body of water in the direction of the observer, each point gets varying directions of electromagnetic waves) . This is kinda what I want fact-checked the most.

P.s. I couldn't find anything useful online, just generic "oh, lightning occurs when clouds polarise" and nothing about the path of the light.

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EmperorGeek t1_j4trkjz wrote

Lightning doesn’t tend to occur in clear skies. There are usually plenty of clouds to reflect the light of the bolt. Clouds being made of small droplets of water, so your assumption of refraction/reflection by water is accurate.

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KettleManCU7 t1_j4ttvp8 wrote

That statement is partially true. Lightning bolts do illuminate the sky, but it is not due to reflection off of aerosols. Lightning is caused by the buildup and discharge of electrical energy within a storm system. The intense heat of the lightning bolt causes the surrounding air to expand rapidly, creating a bright flash and a thunderous sound. The light emitted from the bolt can be reflected off of clouds and other particles in the atmosphere, which can enhance the overall brightness and create different colors in the sky.

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shifty_coder t1_j4vd0wg wrote

More specifically, when the plasma returns to a gaseous state, the extra energy is released as photons.

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Blakut t1_j4ugwil wrote

>. The light emitted from the bolt can be reflected off of clouds and other particles in the atmosphere, which can enhance the overall brightness and create different colors in the sky.

iusn't that what op said? And without tge atmosphere and clouds and such you'd only see the bolt?

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JonJackjon t1_j4tul30 wrote

I agree with this explanation with a minor addition. The plasma created from the lightning discharge is extremely hot. Extreme heat from anything will give off light. This is why incandescent bulb colors are described in °Kelvin.

I don't know the physics of how a hot specimen emits photons.

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MrNobleGas t1_j4uwokd wrote

You're thinking of black-body radiation, the phenomenon where an object emits electromagnetic radiation purely because it has a temperature greater than zero.

There are electric charges inside the object - nuclei and electrons. This creates electric fields. When an object has temperature, its particles move around, which means they undergo acceleration. A charge undergoing acceleration in an electric field scatters that field (which also happens when that field is what caused it to move), which creates propagations in that field - electromagnetic waves - light. The higher the temperature, the higher the energy, and Planck gives us a direct relation between energy and frequency. Higher frequency means shorter wavelength. Sufficiently hot objects will therefore emit visible wavelength, while something as warm as, say, a human body emits lower-energy infrared radiation.

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geek66 t1_j4we80i wrote

And in clear air - like strikes on the edges of a storm, the lightning looks crisp and cleanly defined

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[deleted] t1_j5a8fxi wrote

Thanks to gas excitations, both crackling lightning and brilliantly colored exploding fireworks can send chills up your spine and cause your heart to beat faster.

While the vivid white light we associate with lightning is an example of incandescence, with a temperature in the order of 30,000 K, its colors also stem from gas excitations - light emitted through the excitation of gas molecules in the atmosphere. Gas excitations are a form of luminescence, photons of light being emitted as excited electrons drop back to their initial energy state. Unlike incandescence, luminescence may occur at low temperatures.

Likewise, pyrotechnic experts use incandescence to create brilliant white fireworks, but rely on the phenomenon of gas excitation to create the dance of colors we expect from fireworks. In addition, neon, mercury, and sodium lights take advantage of gas excitations.

https://www.webexhibits.org/causesofcolor/4.html

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