3047: Rotary Tool

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Sunbeam

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Title text: While weather control is typically thought of as a superpower, the unconscious ability of astronomers and astrophotographers to summon clouds is more properly classified as a curse.

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Explanation

Astrophotography is the act of taking pictures of very distant objects. Common subjects of astrophotography include celestial bodies like planets and moons of the solar system, faraway galaxies, nebulae, spacecraft, or even empty patches of the sky.

In order to take such photos, one needs to know where these objects are in the sky. One major problem faced by Earth-based astrophotographers (most of them) is the fact that the Earth rotates. As the Earth rotates, it creates the illusion that the celestial objects being photographed are rotating through the night sky. Therefore, in order to get clear pictures of their subjects, astrophotographers must develop a strong understanding of how objects like a galaxy or the sun move through the sky, so that their cameras can compensate for this rotation and produce clear pictures.

This understanding of how objects move through the sky due to the Earth's rotation is the minor superpower referred to in the comic. As the sun is an example of an object in the sky, the intuition of astrophotographers allows them to predict where the sun will be in the future, and by extension, where the light flooding in through the window will be in the future. With this knowledge, Cueball, who assumingly has this minor superpower, can advise his friends to sit at the far table to avoid the light from the window hitting them. Though normally extra light may be considered desirable, such direct sunlight in this case would probably be considered problematic as there may be excessive heat and/or light. By contrast, the table currently beyond the beams of sunlight would be a perfectly acceptable place to sit and would remain so. There is a chance however that it doesn't actually matter in this scenario which table to sit at, and Cueball is just saying it to show off his ability.

This comic takes place north of the Sun's current ground-track (i.e. the line through the tropics which experience the Sun being directly overhead on any given day of the year, which changes over the course of the year due to the axial tilt of the Earth). In both hemispheres, the Sun can be found rising in the east in the morning, at its highest at around midday (exactly at true local midday, but must be adjusted for timezone issues such as the offset from the nominal local datum and DST effects), then setting in the west in the evening. (At least until you get close enough to the poles to experience no, or barely any, day or night according to the time of year.) Therefore, typically in the subtropical and temperate latitudes of the Northern Hemisphere, a shadow (and, by being framed by shadows, the light flooding in through windows) moves in a clockwise direction, from westerly, then north, then easterly. Similarly, shadows in the Southern Hemisphere move counter-clockwise, from a western direction, via south, eventually towards east. The light from the window in the comic is predicted to move from the center to the left, a clockwise rotation, consistent with the comic being set in the Northern Hemisphere, especially as this comic has been released almost in the middle of the time of the year where this scenario happens only to places north of the equator.

(The declinated angle of the Sun through the window is hard to measure, and without even knowing the time of day we cannot hope to further narrow down the true latitude of the location and which direction the window faces. Although it is typical that, in temperate northern latitudes, major windows like the one shown are set to face as close to south as the orientation of buildings/rooms allow, to make the best use of daylight — particularly in the winter months. It is also a not unreasonable assumption that this meeting (or perhaps a meal) is occuring not long before/after noon, or even during it, with the Sun then approaching its zenith. Overall, it would be possible to see something very like this scene play out for Randall in his current home location, of around 42°N, at this time of year.)

The title text talks about another minor "superpower", that astrophotographers have, which makes clouds always seem to show up in front of the night sky. Because this "ability" is actually just coincidence,^{[citation needed]} that only appears causal to some, as well as that it interferes with their work, by ruining their photos, the title text more accurately classifies it as a curse, which is why the rest of the comic describes astrophotographers having only one "actual" superpower. Of course though, if it was a concious ability it would be more helpful, and could do a similar effect to that in the comic, by moving clouds in front of the sun to put you in shade.

Transcript

This is one of 26 incomplete transcripts: Don't remove this notice too soon. NOTE: This transcript is good enough that it could possibly warrant the removal of this notice, but I will let a more experienced editor decide when to remove it. If you can fix this issue, edit the page!

[Cueball, Megan, and White Hat are in a large dark room, presumably a restaurant, with two tables and a large window, with 4 panels and a topsection. The window is casting a large sunbeam between the two tables.]

Cueball: Let's take the far table.

Cueball: The closer one will be in the sun soon.

[Caption below the panel:]

Astrophotography gives you exactly one extremely minor superpower.

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Discussion

How come it's at 0.017 RPM for a minute?? and yet 1 RPM for a second? pls fix this randall Midnightvortigaunt (talk) 18:01, 5 February 2025 (UTC)

Its 0.017 RPM for the minute hand. The minute hand revolves once per hour or at 1/60 RPM ≈ 0,017 RPM --172.71.148.59 18:14, 5 February 2025 (UTC)

Ohhh that makes sense I didn't think about it like that Midnightvortigaunt (talk) 19:27, 5 February 2025 (UTC)

Mr.Dude (talk) 17:20, 7 February 2025 (UTC) I wonder what torque is needed to launch the average backyard telescope worthy of a tracking mount at Mach 8 given standard state pressures and temperatures of perhaps average conditions found in Randall’s back yard.

How come the comment above is invisible to me? 172.68.245.229 18:03, 5 February 2025 (UTC)

Possibly because people indented with spaces rather than with colons? 162.158.79.77 19:40, 5 February 2025 (UTC)

72 RPM for a record player...? 162.158.74.25 18:08, 5 February 2025 (UTC)

I could only find 78 RPM disks in the german wikipedia. 172.70.114.56 18:41, 5 February 2025 (UTC)

I came here to make the same comment: 72 is most probably a typo. The old records (at this date, very old, since the transition to vinyl records was 1948 to 1958 (in the US)) were 78 rpm, not 72 rpm https://en.wikipedia.org/wiki/Phonograph_record Rps (talk) 19:30, 5 February 2025 (UTC)

72 is (for example) relevent to font sizes (size 1 = 1/72 of an inch, size 72 = 1 inch), which might therefore have envaigled Randall's head for numbers by a different route, and got him confused. Conceivably he has had to deal with playing old 78s, but probably not for a long time... even the retro-revival of vinyl, recently, has probably not had quite so many old old records released to fill such nostalgic needs. So an easy brain-fudge/thinko to trip over on. 162.158.74.48 00:54, 6 February 2025 (UTC)

There used to be a record label call 72RPM records. 172.69.229.146 (talk) 19:07, 5 February 2025 (UTC) (please sign your comments with ~~~~)

We need one of those tables in here. DollarStoreBa'al (talk) 18:37, 5 February 2025 (UTC)

I made a change to the explanation that all of these numbers are realistic because, I checked out the speed of dental drills and they really do rotate that fast. I haven't checked out all of the other tools, but I suspect that they are also accurate. If you find that any of them are misstated, please correct my correction. Rtanenbaum (talk) 22:38, 5 February 2025 (UTC)

TABLE REQUEST When someone uploads a table, I'd like to recommend a second column for the frequency / reciprocal of the speed. "0.000000000073 minutes" is one every 13.7 billion minutes, or ~26,000 years. Thanks! 172.70.46.107 20:20, 5 February 2025 (UTC)

Me again. Should the column header "revolution time" be "rotation time"? In every instance, the axis of motion is within the object itself; even the second/minute/hour hands go around the axis. 141.101.76.73 16:41, 6 February 2025 (UTC)

TRIVIA 16 2/3 RPM phonographs were used for some voice-recorings back in the day. 172.68.26.24 21:01, 5 February 2025 (UTC)

My parent's old record player (60's, probably) had 4 possible speeds: 16, 33, 45, 78. By the early 80's the current ones only had 33 and 45. Rps (talk) 16:59, 7 February 2025 (UTC)

Album goes back to stacks of 78s. A symphony or opera would be 2, 3, 4 or more disks. They were bound like a photo-album with a leaf for each disk. "78" wasn't "standardized" until the format was fading. 3600-rpm motor and 46-tooth gear is incomplete (one tooth gear??) Early discs were from 60 to 130 rpm. Users would adjust speed by ear (also to ease pitch-matching for karaoke). Only as LPs arrived did someone invent the number "78.26 rpm" (no recordplayer and few lathes of the period were near that accurate). --PRR (talk) 02:34, 6 February 2025 (UTC)

Indeed, my parents had a large collection of old records and at least one had a speed marking of 80rpm.--172.68.186.43 09:17, 6 February 2025 (UTC)

With wind-up players, a lot of them started off playing at one speed and ended playing at a completely different one anyway...172.68.186.50 09:43, 6 February 2025 (UTC)

I suspect there's not many consumers needing a Uranium Enrichment Centrifuge... at least outside of a few countries in the Middle East. --172.70.58.6 08:50, 6 February 2025 (UTC)

Might face some regulatory / export license issues too.172.70.86.129 11:34, 6 February 2025 (UTC)

I feel like there was a lost opportunity to have Dr. Who's Sonic Screwdriver on the list. Maybe the rpms are unknown.162.158.159.107 13:05, 6 February 2025 (UTC)

The table says that 0.00070 "seems off; a sidereal day is 23.93 hours". That's just because (like all of the other settings) 0.00070 is quoted with only 2 significant digits. Every period between 23.64 and 23.98 hours would round to 0.00070 RPM. 162.158.134.199 13:58, 6 February 2025 (UTC)

The question I have is: why are dental drill speeds so high? 172.70.247.92 17:21, 6 February 2025 (UTC)

"why are dental drill speeds so high?" It hurts less. (Are you old enough to remember routine use of belt-driven dental drills?) You can cut a given amount of material (wood, steel, tooth) quickly with heavy force or high speed. Neither is really fun, but hi-speed is generally preferred. --PRR (talk) 19:08, 6 February 2025 (UTC)

Although some materials behave badly to heat (either work-hardening, for some alloys, or melting/burning, like plastics) and that's why variable-speed hand-drills/etc usefully have low speeds (for essentially the same force, when that's done via reostat rather than an actual gearbox). On the few occasions I've had my teeth drilled, I'm pretty sure I've detected the pungent smell of fried tooth-fragments, but it was nothing like as strong as smelling my own nose-flesh being burnt one of the times I had it cauterised to try (and fail) to prevent excessive nosebleeds. 172.69.79.139 21:15, 6 February 2025 (UTC)

The latest NMR CPMAS probes send their rotors to go at 9.6 Mrpm, M=mega. [1] --172.69.109.172 21:56, 7 February 2025 (UTC)

Should we list the rotor diameters to achieve the mach 8 speed mentioned in the title text in the table? I don't think that we should. guess who (if you desire conversing | what i have done) 06:01, 24 February 2025 (UTC)

I (obviously since I worked it all out) think it is in the spirit of the ridiculous idea of the comic and XKCD generally to do these calculations. That said, I'm getting different numbers than your update to make it Mach 8. Denver87 (talk) 16:21, 24 February 2025 (UTC)

I get the following: 4,799au, 74,866km, 37,733km, 3,144km, 52.4km, 1,588m, 1,165m, 728m, 175m, 34.9m, 21.0m, 149.7cm, 87.3cm, 174.7mm. Denver87 (talk) 16:21, 24 February 2025 (UTC)

Happy to share calculation notes, but here's the example for the dental drill: 300,000rpm = 5,000 rps; diameter of: 174.7mm --> circumference of: pi * 174.7mm = 548.8mm; 548.8mm * 5000rps = 2,744,000mm/sec = 2744m/sec; Mach 8 = 8 * 343m/sec = 2744m/sec. Denver87 (talk) 16:21, 24 February 2025 (UTC)

If you agree with the calculations, one of us can at least update it. Denver87 (talk) 16:21, 24 February 2025 (UTC)
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