https://www.explainxkcd.com/wiki/api.php?action=feedcontributions&feedformat=atom&user=Chrisnyt 2026-05-17T00:58:14Z User contributions MediaWiki 1.30.0 https://www.explainxkcd.com/wiki/index.php?title=2027:_Lightning_Distance&diff=160665 2018-08-01T12:25:29Z

<p>Chrisnyt: /* Explanation */</p> <hr /> <div>{{comic<br /> | number = 2027<br /> | date = August 1, 2018<br /> | title = Lightning Distance<br /> | image = lightning_distance.png<br /> | titletext = The index of radio refraction does have a lot of variation, which might throw off your calculations, so you can also look at the difference in brightness between the visible flash and more-attenuated UV and x-rays.<br /> }}<br /> <br /> ==Explanation==<br /> {{incomplete|Created by a kid who is scared of thunder and lightning - Please change this comment when editing this page. Do NOT delete this tag too soon.}}<br /> The usual trick for determining the distance to a {{w|lightning}} flash is to count the seconds until you hear {{w|thunder}} and divide by five to get miles (or three to get kilometers). This works because the {{w|speed of light}} is essentially instantaneous over the relevant distances, while the {{w|speed of sound}} is 1087 ft/sec (varying a bit based on temperature), or about 1/5 mile/second. <br /> <br /> However, the speed of electromagnetic radiation, which includes light, is not truly infinite, being 186,282 mi/sec in a vacuum. Lightning is not traveling in a vacuum and is slowed by air in a fashion which depends on its frequency. With sufficiently precise instruments, it would theoretically be possible to use this effect to determine the distance to a lightning flash, as proposed by Randall. The joke is that it is impractical for humans, both because we can't measure such small time intervals and because we can't detect radiation outside the visible spectrum.<br /> <br /> ==Transcript==<br /> {{incomplete transcript|Do NOT delete this tag too soon.}}<br /> <br /> {{comic discussion}}</div>

Chrisnyt