explain xkcd - User contributions [en]

Talk:2809: Moon

2023-08-01T05:21:56Z

172.70.90.187:

Happy birthday to me. This comic is a good birthday present, so I'm gonna try to add some stuff to the explanation now. [[User:R3TRI8UTI0N|R3TRI8UTI0N]] ([[User talk:R3TRI8UTI0N|talk]]) 02:11, 1 August 2023 (UTC)

Okay, added a Trivia section and a lot of stuff to the explanation. Request someone help add more information about lunar cycles and some wikipedia links. [[User:R3TRI8UTI0N|R3TRI8UTI0N]] ([[User talk:R3TRI8UTI0N|talk]]) 02:35, 1 August 2023 (UTC)
:Ah, well, I added more (sufficient? ...haven't wikilinked yet) info about the illumination/tide cycles. i.e. about half the time (at least) half reilluminating areas on the night side of Earth + roughly twice a day dragging/flinging the tides 'upwards' (modifying the Sun's own twice-daily effects).
:Had to heavily qualify the secondary Trivia point, for caveats. I mean selenically-specific names aren't rare, when refering to orb sometimes known as Phoebe/Cynthia, until you become more precise about "common English use". Didn't say anything about (the) Earth, but did mention the Sun(/suns in general) in the edit comment. Interesting point to make, but not so much unusual as stemming from long time (way into prehistory!) custom so really being the heavily weighted precedent. [[Special:Contributions/172.70.90.187|172.70.90.187]] 05:21, 1 August 2023 (UTC)

If there was no Moon, would an Earth astronomer that discovered moons around one of the other planets be considered a loony? [[User:These Are Not The Comments You Are Looking For|These Are Not The Comments You Are Looking For]] ([[User talk:These Are Not The Comments You Are Looking For|talk]]) 02:40, 1 August 2023 (UTC)
:If there was no moon, it's quite possible there would be no intelligent life on Earth. Also, when Galileo Galilei found Jupiter's moons, he was totally considered loony by some, while others said it's defect of the telescope. Remember that at that point of history, suggesting that if Earth has moon, other planets might have one too was something you could be burned on stake for. -- [[User:Hkmaly|Hkmaly]] ([[User talk:Hkmaly|talk]]) 03:13, 1 August 2023 (UTC)

I doubt the title text is intended as a reference to that saying. [[Special:Contributions/172.69.247.51|172.69.247.51]] 04:17, 1 August 2023 (UTC)

2803: Geohydrotypography

2023-07-18T03:43:29Z

172.70.90.187: /* Transcript */

{{comic
| number = 2803
| date = July 17, 2023
| title = Geohydrotypography
| image = geohydrotypography_2x.png
| imagesize = 339x389px
| noexpand = true
| titletext = The Atlantic is expanding at about 10 ppm (points per month).
}}

==Explanation==
{{incomplete|Created by a Geohydrotypographologist - Please change this comment when editing this page. Do NOT delete this tag too soon.}}

This comic is another entry in the "[https://www.explainxkcd.com/wiki/index.php/Category:My_Hobby My Hobby]" series of comics.

[[wikipedia:Plate tectonics|Plate tectonics]] is the theory that the earth's lithosphere is comprised of tectonic plates, which carry the continents. Here, Randall explains that if the surface of the Atlantic Ocean were covered in printed text (as if its surface were a giant sheet of printed paper, which it is not {{citation needed}}), the shifting of the continents would increase the amount of text by about 100 words per second.

[[Randall]] says that his hobby is geohydrotypography, which is a portmanteau of [[wikipedia:Geology|geology]], [[wikipedia:Hydrology|hydrology]], and [[wikipedia:Typography|typography]]. Basically, it means that his hobby is typing on rocks and ocean.

The title text reports the rate of the ocean's expansion, about 40 millimeters per year, in points per month. A point in typography is 0.3528 millimeters.

==Transcript==
{{incomplete transcript|Do NOT delete this tag too soon.}}
:[A depiction primarily of the Atlantic Ocean and the surrounding land-masses. The land is black, leaving the oceans and seas white except for the following words written in sixteen lines of text (from just below the tip of Greenland/Arctic Ocean down to slightly above the Falkland Islands/Southern Ocean) that are, for the most part, wrapped between the Atlantic coastline 'margins' (as defined by the Americas on the left and Europe/Africa on the right, or significant island groups:]

:If you covered the surface of the Atlantic Ocean with twelve-point printed text, with the lines wrapping at the coasts, the expansion of the ocean basin due to plate tectonics would increase your word count by about 100 words per second.

:[Caption below the panel:]
:My hobby: Geohydrotypography

{{comic discussion}}

[[Category:My Hobby]]

316: Loud Sex

2023-06-29T09:56:10Z

172.70.90.187: /* Explanation */ Circular aberration

{{comic
| number = 316
| date = September 14, 2007
| title = Loud Sex
| image = loud_sex.png
| titletext = Spherical or parabolic reflectors would of course lead to aberrant behavior.
}}

==Explanation==
[[Cueball]]'s neighbor likes to engage in loud sex, which keeps Cueball awake at night, and she pretends to apologize for it as a way of bragging, so Cueball wants to get revenge. A simple way would be to inflict the same to her in retaliation by having loud sex when she is not. But Cueball adds a science nerd's touch to it, with an elliptical reflector dish. As shown on the schema, such a dish reflects the sound waves in a way that all waves originating from a specific point (the first focus of the ellipse the dish's shape is based on) converge after reflection to a specific other point (the second focus of the same ellipse).<sup>[1]</sup> Cueball calibrates and installs his elliptical dish in such a way that all the sound coming from his loud girlfriend's head during sex is concentrated after reflection to his neighbor's head in her bed. This makes his loud sex far louder to her than hers was to him.

The title text makes a {{w|double entendre}}. A spherical mirror can cause the signal from across the reflector to not focus at the same spot -- {{w|spherical aberration} -- but the play on words leads the reader to believe that aberrant sexual behavior would occur. (Parabolic mirrors do not suffer from this kind of aberration.)

<small>[1]: Note: that is actually the behaviour of an ''{{w|ellipsoid}}al'' reflector dish, or an elliptic one in two dimensions; but in 3D an elliptic one works similarly, only converging waves from a line to another line, instead of points.</small>

==Transcript==
:My neighbor has loud sex.
:[Cueball in bed, covering his head with a pillow. There is sound coming from outside.]
:''OHHHHH''
:''GASP''
:''AAAAAAA''
:Good for her and all, but it keeps me up at night.

:And she's so smug about it.
:[Cueball and neighbor coming out of their apartments.]
:Neighbor: Sorry, could you hear us last night? Oh, you know how it gets sometimes.
:Cueball: Not really...

:But tonight I finally get my revenge. Because now I have a loud girlfriend too.
:[Megan with "LOUD" and an arrow pointing to her.]

:And an elliptical reflector dish.
:[Diagram of an elliptical reflector dish.]

:[Cueball and Megan having sex, with the dish behind them reflecting the sex sound effects, in a way that they focus, through walls, on his neighbor sitting up in bed while holding her head in pain.]

==Trivia==
*This comic is referred to in [[368: Bass]], where [[Black Hat]] mentions in the title text that he is annoyed by "the guy upstairs with the loud girlfriend and the elliptical dish."
*Cueball doesn't have hair in the first and second panels, but he does in the last.
{{comic discussion}}
[[Category:Comics featuring Hairy]]
[[Category:Comics featuring Cueball]]
[[Category:Comics featuring Megan]]
[[Category:Sex]]
[[Category:Physics]]

2624: Voyager Wires

2022-05-26T17:27:47Z

172.70.90.187: Undo revision 279056 by Donald Trump (talk)

{{comic
| number = 2624
| date = May 25, 2022
| title = Voyager Wires
| image = voyager_wires.png
| titletext = Also, they're getting increasingly worried that someone will accidentally hit the 'retract' button, and that the end of the cable thrashing around as it winds up could devastate the Earth's surface.
}}

==Explanation==
{{incomplete|Created by a WIRE CUT BECAUSE OF BUDG- are you there houston? it's me v----ger, you'll never guess what I found! Please change this comment when editing this page. Do NOT delete this tag too soon.}}
This comic claims that the {{w|Voyager program|Voyager probe}}s communicate with NASA though ridiculously long copper wires. These wires would have to be continuously lengthened as the probes travel away from Earth. Supposedly, because of "high copper prices and budget constraints," they may not be able to afford to lengthen the wires much longer. If this occurred, they would have to either cut the wires or let them break, which would prevent any further communication with the probes. In reality [https://voyager.jpl.nasa.gov/mission/status/ they use radio waves], not long copper wires, so this will not actually happen.

If copper wires were dragged by the Voyager probes, assuming a 1mm² thick cable, 550 tons of copper would be needed per hour and it would add 1 million Ohm per hour to the cable resistance. At [https://www.moneymetals.com/copper-prices $8,560/ton], this would cost $41 billion dollars/year, which would be nearly twice [https://www.planetary.org/space-policy/nasas-fy-2022-budget NASA's entire annual budget].

The resulting wire would slow down the probes by drag, but be perfect space elevators for lightweight spacecraft.
Since the Earth spins, the wires would also spool around the Earth, slowing the probes down even further. Clearly, this is not a good idea.{{Citation needed}} This problem might be avoided if the wires reached earth at one of the poles. Or perhaps they could go to an airplane that flies around earth at exactly 15 degrees of longitude per hour, with periodic air-to-air refueling, so that it is always on the side of the earth facing the probe.

Because the Voyager probes aren't in the plane of the earth's orbit around the sun, the Earth would not, in its rotation around the sun, drag these copper wires through the sun. If it did, the wires would melt.{{Citation needed}}

The title text references the phenomenon seen with self-retracting cables, such as are commonly found on vacuum cleaners, where the free end of the cable, where the plug is, oscillates more and more wildly as the cable approaches full retraction, leading to the danger of a painful rap on the hand if it is not withdrawn in time. A planet-sized impact of this kind could cause severe damage.

A few days before this comic was released, [https://voyager.jpl.nasa.gov/news/details.php?article_id=124 NASA had reported] receiving corrupted attitude data from the Voyager 1 probe. The fact that they are receiving any data at all means that the attitude control system must be working (or else the antenna would not point at Earth), but they continue to investigate how that data could be corrupted after that point.

;Spoiler alert
The consequence of a cable between a craft in space and a planetary location being suddenly retracted was recently imagined in the first episode of the Apple TV+ series ''{{w|Foundation (TV series)|Foundation}}'', wherein a {{w|space elevator}} tether was severed. [https://www.youtube.com/watch?v=huRmvG3zRpg It didn't end well for anyone other than the terrorists] who won the freedom of thousands of inhabited worlds which had formerly suffered under the jackbooted oppression of {{w|Trantor}}'s fascist galactic Empire regime.

==Transcript==
:[In the bottom right corner is a space probe, with large satellite dish and long antenna. Behind it runs a long wire, that makes three loops before it is connected to North America on the Earth in the top left corner. To the left of the Earth there is a second wire, which goes off-panel to the left. Below the panel there is a caption:]
:Sad news: Due to high copper prices and budget constraints, NASA may finally have to cut the wires that they've been spooling out to communicate with Voyager 1 and 2.

{{comic discussion}}

[[Category:Space probes]]