Is there such a thing as heat lightning?

Dear Cecil:

For a long time I have been debating this point with friends: I say there is no such thing as heat lightning. I say it is just lightning occurring far off in the sky, and all we see is the glow from the bolt. Who's right?

Cecil replies:

You are, as long as you’re not getting your heat lightning mixed up with your sheet lightning. Heat lightning, the sudden reddish glow you sometimes see on warm summer nights, looks the way it does (and sounds the way it does, i.e., silent) because of its distance from you, the observer. At its source, it looks like regular old blue-white lightning; what makes it appear reddish from a distance is the atmosphere’s propensity for scattering light on the blue end of the spectrum, the same phenomenon that produces red sunsets.

Much more common than heat lightning, however, is sheet lightning, which is produced by a discharge within a cloud rather than one from cloud to ground. Here the electrical channel is obscured by a cloud, and all you see is a huge sheet of illuminated cotton, or whatever it is they’re making clouds out of these days.

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