Editing 2027: Lightning Distance
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− | + | =Explanation= | |
+ | {{incomplete|Created by a RADIO BURST - Update calculations and added values in km and miles. Do NOT delete this tag too soon.}} | ||
The usual trick for determining the distance to a {{w|lightning}} flash is to count the seconds from when you see the flash until when you hear {{w|thunder}}, and divide by five to get miles (or three to get kilometers). This works because the {{w|speed of light|transmission of light}} is essentially instantaneous over the relevant distances, while the {{w|speed of sound}} is 331.2 m/s (1,087 ft/s, 1,192 km/h, or 741 mph, varying a bit based on temperature), or about 1/5 mile per second (1/3 kilometer per second). | The usual trick for determining the distance to a {{w|lightning}} flash is to count the seconds from when you see the flash until when you hear {{w|thunder}}, and divide by five to get miles (or three to get kilometers). This works because the {{w|speed of light|transmission of light}} is essentially instantaneous over the relevant distances, while the {{w|speed of sound}} is 331.2 m/s (1,087 ft/s, 1,192 km/h, or 741 mph, varying a bit based on temperature), or about 1/5 mile per second (1/3 kilometer per second). | ||
− | This comic subverts the usual trick by having Megan describe a highly impractical alternative method. Megan's method is based on the fact that the speed of electromagnetic radiation, which includes light and radio waves, is not truly | + | This comic subverts the usual trick by having Megan describe a highly impractical alternative method. Megan's method is based on the fact that the speed of electromagnetic radiation, which includes light and radio waves, is not truly infinite. The radiation produced by lightning on Earth also has to travel through air, which changes its speed in a fashion which depends on its frequency. |
− | + | According to {{w|List_of_refractive_indices|Wikipedia}} and [https://hypertextbook.com/facts/2005/MayaBarsky.shtml other sources], refractive index of air at 0°C is about 1.000277, which equates to a speed of light around 299709.4 km/s (186230.8 miles/s). According to [https://www.fig.net/resources/proceedings/fig_proceedings/fig_2002/Js28/JS28_rueger.pdf this paper], refractive index for radio waves in similar conditions is 1.000315, which equates to a speed around 299698.1 km/s (186223.7 miles/s). This means that to get the distance, the time difference in seconds between visible flash and radio burst should be multiplied by about 4.9 billion for miles, or about 7.9 billion for kilometers. More details for the calculations are in the comments below. | |
− | + | With sufficiently precise instruments, it would theoretically be possible to use this effect to determine the distance to a source of extremely short bursts of visible light and radio waves. The joke is that it is impractical for humans, both because we can't measure such small time intervals (one nanosecond for every 4.9 miles or 7.9 kilometers of atmosphere) and because we can't detect radiation outside the visible spectrum without very specialized instruments. Even with specialized instruments, we probably couldn't measure the light and radio wave emissions of lightning with sufficient precision because a flash is not instantaneous, but lasts about 60 to 70 microseconds - about five {{w|orders of magnitude}} longer than the time difference we would need to measure. | |
− | + | For the purpose of the joke, the "5 billion" value used in the comic is a fair estimate which also references the original rule of 5 seconds per mile nicely, though the result can have a huge margin of error depending on actual conditions (temperature, humidity, etc.), as the title text suggests ("the index of radio refraction does have a lot of variation"). | |
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− | + | Even if lightning was farther away, for example, if we were observing another planet, the time difference still would not be substantial, because the visible and radio waves travel at essential the same speed as each other in the vacuum of space (the difference in speed discussed above applies only to travel through air). | |
− | The title text suggests another method of calculating | + | The title text suggests another method of calculating distance to lightning. Since the absorption of light is also different in different wavelengths, it would be possible to calculate the difference by comparing the brightness instead of delays. This would, however, require the knowledge about prior relative brightness of lightning, i.e. the spectrum, in the compared wavelengths. |
==Transcript== | ==Transcript== | ||
+ | {{incomplete transcript|Do NOT delete this tag too soon.}} | ||
:[Cueball and Megan stand on either side of a window, observing a bolt of lightning in a dark sky.] | :[Cueball and Megan stand on either side of a window, observing a bolt of lightning in a dark sky.] | ||
:Cueball: What's that trick for telling how many miles away lightning is? | :Cueball: What's that trick for telling how many miles away lightning is? | ||
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[[Category:Comics featuring Cueball]] | [[Category:Comics featuring Cueball]] | ||
[[Category:Comics featuring Megan]] | [[Category:Comics featuring Megan]] | ||
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