explain xkcd - User contributions [en]

3189: Conic Sections

2026-01-03T05:21:34Z

Lxylxy123456: /* Explanation */ Fix Wikipedia link

{{comic
| number = 3189
| date = January 2, 2026
| title = Conic Sections
| image = conic_sections_2x.png
| imagesize = 288x322px
| noexpand = true
| titletext = They're not generally used for crewed spacecraft because astronauts HATE going around the corners.
}}

==Explanation==
{{incomplete|This page was created recently. Don't remove this notice too soon.}}
A {{w|Kepler orbit}} describes the simplified motion of two celestial objects around each other based only on their gravitational forces, ignoring any other factors such as gravity of other objects, atmospheric drag, and non-spherical bodies. Such an orbit will form a {{w|conic section}}. Conic sections are curves formed by the intersection of a plane and a {{w|cone}}. This results in four possible curves: a circle, ellipse, parabola, or hyperbola, depending on the angle of the plane relative to the cone's axis.

In real conic sections, the cone extends to infinity. In the comic, however, the "conic section" representing the satellite's orbit has a base, resulting in sharp corners where the base and the lateral surface meet. As alluded to in the title text, these corners would be extremely uncomfortable for an astronaut in a crewed spacecraft such an extreme and sudden change in direction would require a very large, potentially dangerous G-force.

==Transcript==
{{incomplete transcript|Don't remove this notice too soon.}}
:[A view of the Earth, focused on Asia and the Indian Ocean with East Africa at left and the Western Pacific and Australia at right. A satellite is shown in an unusual orbit around the planet.]
:[Caption below the panel:]
:All Keplerian orbits are conic sections. For example, this one uses the base of the cone.
{{comic discussion}}<noinclude>

[[Category:Space]]
[[Category:Geometry]]

2772: Commemorative Plaque

2023-05-06T17:07:25Z

Lxylxy123456: Add link to Wikipedia "Commemorative plaque"

{{comic
| number = 2772
| date = May 5, 2023
| title = Commemorative Plaque
| image = commemorative_plaque_2x.png
| imagesize = 422x282px
| noexpand = true
| titletext = [Below] On this site on May 12th, 2023, I finally learned how to use the masonry bit for my drill.
}}

==Explanation==
{{incomplete|Created by a MASONRY BIT DONE BY DRILL - Please change this comment when editing this page. Do NOT delete this tag too soon.}}
The narrator discovered that it is simple and inexpensive to have a {{w|commemorative plaque}} made, and so had a commemorative plaque made to record that event. This comic is similar to previous comics, such as [[2682: Easy Or Hard]]. The comic both indicates the lack of knowledge many people have about how simple or difficult it is to do a certain thing, and the over-the-top response a person might have to a relatively mundane discovery.

The comic was published on May 5, the holiday of {{w|Cinco de Mayo}}. The comic subverts an expectation that a plaque about May 5 would be to commemorate either the 1862 {{w|Battle of Puebla}}, which took place on May 5 and inspired the holiday, or, after the reader notices the year on the plaque, some 2023 event related to the holiday.

The title text tells us that it was a week later when they learned out how to use a {{w|Drill_bit#Masonry_drill_bit|masonry bit}} to mount the plaque, there being some small but useful points of technique to be learnt when drilling into one or other of stone, brick, concrete or cement. It equates it being almost exactly as much deserving of a plaque as the very act of obtaining a plaque, and now a second one, to also have finally been able to properly attach it (them) to the chosen wall.

==Transcript==
:[A light gray brick wall with a plaque on it. The plaque has a white background and its frame is gray. It has been attached to the wall with four pins one at each corner. The plaque reads:]
:On this site on
:<big><big>'''May 5th, 2023'''</big></big>
:I realized that you could order custom commemorative plaques online that say
:<big>'''whatever you want''' </big>
:and it's not that expensive

{{comic discussion}}

2744: Fanservice

2023-03-01T20:33:05Z

Lxylxy123456: Fix wiktionary link

{{comic
| number = 2744
| date = March 1, 2023
| title = Fanservice
| image = fanservice_2x.png
| imagesize = 188x278px
| noexpand = true
| titletext = I was eventually kicked out of my architectural engineering program because I wouldn't stop referring to HVAC as "the fandom."
}}

==Explanation==
{{incomplete|Created by an HVAC ROCK BAND - Please change this comment when editing this page. Do NOT delete this tag too soon.}}

This comic is very similar to [[2036: Edgelord]] and [[2654: Chemtrails]]. In all three of these comics, a modern slang term or just a commonly used word ("chemtrails" was the case in 2654) is used to describe a job, and while the slang or word seems accurate, it isn't the normally used term for the job. Previously a graph theory PHD was labeled an "edgelord", a reference to how mathematical graphs have edges, but this time a turbine maintenance engineer is called out for doing a lot of fanservice, as in, literally serving/maintaining a huge fan (with which turbines are often inaccurately conflated). In the other comic, trails of ant pheromones were labeled as "chemtrails", a reference to how pheromones are chemicals.

A second order of dissonance is introduced from the difference between fans and turbines, which are designed to work towards opposite purposes. Randall has previously touched on wind turbines ''not'' being fans, most notably in [[1378: Turbine]].

{{wiktionary|fanservice|Fanservice}} is a term often used to describe certain decisions made in TV or film productions that make some form of knowing nod to the viewers that isn't necessary to the plot or visualization of the work. It can just mean inserting obscure details of the work's back-history, to spark gleeful recognition amongst the more devoted fans, or it could be increasing the ridiculousness of character's behavior (often due to one or other overly contrived reason) to live up to their stereotype. A frequent form of this is the {{tvtropes|MsFanservice|Ms. Fanservice}} trope, where the more glamorous female characters find themselves in more figurehugging clothing, clothing that actually covers {{tvtropes|ChainmailBikini|much less of their figure}} than should be practical or even find themselves shoehorned into a situation where they {{tvtropes|CensorSuds|aren't wearing}} even their 'normal' skimpy outfit.

In the title text, Cueball refers to HVAC (a term for the unified heating, ventilation, and air conditioning systems of a given building) as "the fandom." Normally, "fandom" means the group of fans of something, but here refers to a system that relies on lots of fans.

==Transcript==
{{incomplete transcript|Do NOT delete this tag too soon.}}

:[Cueball stands next to White Hat, who has his hands balled into fists and has small lines above his head to indicate annoyance.]
:Cueball: So, I hear you do a lot of fanservice.
:White Hat: '''''No!'''''

:[Caption below the panel:]
:How to annoy a turbine maintenance engineer

{{comic discussion}}

[[Category:Comics featuring Cueball]]
[[Category:Comics featuring White Hat]]
[[Category:Puns]]
[[Category:Engineering]]
[[Category:Banned from conferences]]
[[Category:How to annoy]]

1799: Bad Map Projection: Time Zones

2017-02-15T05:45:20Z

Lxylxy123456: /* Transcript */ Add Transcript

{{comic
| number = 1799
| date = February 15, 2017
| title = Bad Map Projection: Time Zones
| image = bad_map_projection_time_zones.png
| titletext = This is probably the first projection in cartographic history that can be criticized for its disproportionate focus on Finland, Mongolia, and the Democratic Republic of the Congo.
}}

==Explanation==
{{incomplete|First draft}}This comic shows a [[wikipedia:Map projection|map projection]] where countries are placed according to the [[wikipedia:Time zone|time zones]] they fall under. Based on the way the Sun shines on the Earth, these time zones, which are based on the sun's position in the sky, would best be divided by roughly longitudinal (North-to-South Pole) lines.

However, this is not the case in practice, as the defined time zones tend to have very jagged boundaries. Since [[Randall]] knows he cannot fix the boundaries of the time zones, he instead "fixes" the world by making a map appear to match up with the ideal time zone system. This results in bizarre distortions such as the large, gum-like strands of Greenland and the split upper part of Russia.

Due to the projection, small countries that happen to cross the boundaries of time zones appear as much larger than they actually are. Other map projections distort countries this way, too, but based on their actual physical location as opposed to their position on imaginary time zones. The [[wikipedia:Mercator projection|Mercator projection]] is infamous for distorting Greenland in this way, to the point that it appears to be larger than Africa despite being nowhere near this large size. The title text lampoons the fact that the same phenomenon occurs on Randall's bad map projection, but for countries that do not tend to experience this on typical projections. Much smaller, lesser-known countries such as Finland, Mongolia, and the DRC, which all appear much bigger than their actual size due to being stretched across multiple time zone boundaries.

==Transcript==
{{incomplete transcript}}
:Bad map projection #79:
:'''Time Zones'''
:Where each country should be,
:based on its time zone(s)

{{comic discussion}}

899: Number Line

2017-02-15T05:13:14Z

Lxylxy123456: /* Explanation */ Add a link to Wikipedia

{{comic
| number = 899
| date = May 16, 2011
| title = Number Line
| image = number line.png
| titletext = The Wikipedia page List of Numbers opens with "This list is incomplete; you can help by expanding it."
}}

== Explanation ==

Once again, Randall seems to be just messing around, this time with a number line.

*'''Negative numbers''' have the same magnitude as positive numbers but can only be used to represent the removal of that same magnitude (hence the term "difference" being used for subtraction).

*'''0.99'''.... is {{w|0.999...|equal to 1}} because there is no number between 0.99.... and 1. 1 - '''0.0000000372''' is 1 bit less than the {{w|IEEE_floating_point|IEEE 754 32-bit floating-point representation}} of 1.

*The '''{{w|golden ratio}}''' or "phi" is the number (1 + sqrt(5)) / 2, about 1.61803. It has many interesting mathematical properties, mostly relating to geometry, and has occasional appearances in nature, such as spirals formed by the seeds in sunflowers. It is also subject to many less credible claims, such as the belief that phi appears in {{w|Parthenon}} (a well-disputed claim) or that rectangles proportioned after phi are more aesthetically pleasing.

* The approximate range from 2.1 to 2.3 is marked as '''The Forbidden Region'''. Why Randall marked this range as forbidden is really anyone's guess; it seems to be an entirely arbitrary designation.

*'''{{w|e (mathematical constant)|e}}''' (Euler's number) is 2.71828... and '''π''' (pi) is 3.14159265...

*'''2.9299372''' is a President's Day reference. It is the average of e and pi just as the American Presidents' Day is always observed on the 3rd Monday of February (between {{w|George Washington}} and {{w|Abraham Lincoln}}'s birthdays). Washington and Lincoln were the 1st and 16th Presidents of the USA, respectively. Each has a celebrated place in American history.

*'''{{w|Gird}}''' is a purely fictional number. (The glyph that Randall uses seems to resemble an older shape of the digit 4, such as seen on [http://www.bl.uk/learning/images/mappinghist/large2296.html archaic maps].). Canon and orthodox are references to organised religions. Gird could be a reference to any or all of:
**[http://www.strangehorizons.com/2000/20001120/secret_number.shtml Bleem] - a fictional integer between 3 and 4
**iCarly's [http://icarly.wikia.com/wiki/Derf Derf] - a fictional integer between 5 and 6
**George Carlin's [http://www.urbandictionary.com/define.php?term=bleen Bleen] - a fictional integer between 6 and 7
**[http://www.scp-wiki.net/scp-033 SCP-033] - a fictional number that causes freaky things to happen
**Saturday Morning Breakfast Cereal's [http://www.smbc-comics.com/index.php?id=3913 Sorf] - a fictional integer between 2 and 3

*'''Site of the Battle of 4.108''' is another map joke, implying that 4.108 is an actual location, where an eponymous battle was previously fought. It may be a reference (or homage) to the {{w|Battle of Wolf 359}}, a famous military conflict in the fictional universe of Star Trek.

*An '''Unexplored''' region obscures the line approximately ranging all values from from 4.5 to 6.7. In the days when the Earth was still being mapped out, territories that had yet to be properly explored and charted were labelled in a similar manner. The placement of the '''Unexplored''' region on the number line indicates that all numbers in that range, including the integers 5 and 6, are completely unknown. This is, of course, patently ridiculous, and the humor seems to derive solely from how nonsensical and unbelievable it is.

*It is often the case in the media that "It has been 7 years..." or "In the last 7 years..." etc. It is made to seem like a believable statistic but cannot always be true. Alternatively, it is intended as an absurd joke that the number 7 is just "not to be believed".

*'''8''' is not the largest even prime, nor is it a prime at all. The largest (and only) even prime is 2. A joke intended for those who clearly know that the claim is false.

*The last entry seems to be a reference to certain fields of {{w|pure mathematics}}, which focuses less on performing calculations with numbers and more on understanding structures that may be described using logic. It finishes off the tone of the comic that seems to be shaping the number line terms of what is commonly useful to certain areas of applied mathematics, rather than a complete, accurate version of the number line.

The title text is a literalism joke, implying that Wikipedia would like its "{{w|List of numbers}}" page to include every number from negative infinity to infinity. It could also be a reference to {{w|Gödel's incompleteness theorems}}, which [[Randall]] has used as comic fodder before in [[468: Fetishes]]. Gödel's theorems roughly assert that a number theory could never be fully complete. The equivalent for a list of numbers is {{w|Cantor's diagonal argument}}, which is a proof that any list of real numbers can never be complete even if the list is infinitely long. Either way, any "true" Wikipedia article named "List of numbers" would perforce forever be incomplete, no matter how much it was expanded. Both Gödel's incompleteness theorems and Cantor's diagonal argument feature prominently in {{w|Gödel, Escher, Bach}} by {{w|Douglas Hofstadter}}, to whom Randall devoted later comic [[917: Hofstadter]]. It may also be referencing his previous statements about Wikipedia being the home of compulsive list-makers, who make the most astonishingly complete lists imaginable.

== Transcript ==
:[Number line ranging from -1 to 10.]
:[Arrow pointing left, towards negative numbers] Negative "imitator" numbers (do not use)
:[Line right before the number one] 0.99... (actually 0.0000000372 less than 1)
:[Line at the golden ratio.] Φ - Parthenon; sunflowers; golden ratio; wait, come back, I have facts!
:[Line at a region between two and 2.2] forbidden region
:[Line at Euler's number.] e
:[Line a bit before 3] 2.9299372 (e and pi, observed)
:[Line at π.] π
:[Line at 3.5 with a ribbon as the numeral] Gird - accepted as canon by orthodox mathematicians
:[Line a bit after 4.] site of battle of 4.108
:[Blob between 4.5 and 6.5 labeled unexplored.]
:[Line at seven.] Number indicating a factoid is made up ("every 7 years...", "science says there are 7...", etc)
:[Line at eight.] Largest even prime
:[Line at 8.75.] If you encounter a number higher than this, you"re not doing real math

{{comic discussion}}
[[Category:Math]]
[[Category:Wikipedia]]