explain xkcd - User contributions [en]

3011: Europa Clipper

2024-11-14T14:39:42Z

141.101.69.30: /* Explanation */ Nothing was named after the continent.

{{comic
| number = 3011
| date = November 13, 2024
| title = Europa Clipper
| image = europa_clipper_2x.png
| imagesize = 333x356px
| noexpand = true
| titletext = They had BETTER make this a sample return mission.
}}

==Explanation==
{{incomplete|Created by a JOVIAN DESSERT. Please consider deleting this tag too soon, but refrain from doing so.}}

[[File:Animation of Europa Clipper trajectory around Jupiter.gif|thumb|right|The ''Europa Clipper's'' projected course around {{w|Jupiter}}, represented as the stationary green dot. In gold is Jupiter's moon {{w|Callisto (moon)|Callisto}}, in cyan is the moon {{w|Europa (moon)|Europa}} — the primary target of the spacecraft's study — and in orange-red is the innermost of Jupiter's four {{w|Galilean moons|"Galilean"}} moons, {{w|Io (moon)|Io}}. The spacecraft's track is shown in magenta. Jupiter's largest moon {{w|Ganymede (moon)|Ganymede}} and its second largest moon {{w|Titan (moon)|Titan}} are not shown, but their gravitational pull affects the ''Clipper's'' trajectory. A mission goal is to achieve a 6:1 {{w|orbital resonance}} with Europa by September 2034.[https://www.researchgate.net/profile/Martin-Ozimek/publication/383115312_AAS_24-433_Europa_Clipper_Mission_Analysis_Pump_Down_Trajectory_Design/links/66bcd845311cbb094938dbd6/AAS-24-433-Europa-Clipper-Mission-Analysis-Pump-Down-Trajectory-Design.pdf] ]]

The ''{{w|Europa Clipper}}'' space probe was launched from the {{w|Kennedy Space Center}} in Florida on October 14, 2024. It is expected to arrive at Jupiter and begin exploration of Jupiter's moons, particularly {{w|Europa (moon)|Europa}}, in April of 2030.

Europa is an icy moon. Water ice covers its surface. Beneath the ice, there is expected to be liquid water, which might contain living microbes.[https://europa.nasa.gov/why-europa/ingredients-for-life/] To sample this liquid, its crust (water ice) would need to be broken.

In the comic, Europa's surface ice is likened to the caramel crust on the dessert ''{{w|crème brûlée}}'' which, to eat typically has its crust broken with a spoon. It is believed to have been [https://archive.org/details/lagastronomieaug00sabb/page/272/mode/2up invented in Europe], which ultimately appears to share an [[1010: Etymology-Man|etymological root]] with the moon's name (and thus the subsequent spacecraft), by way of {{w|Europa (consort of Zeus)|greek mythology}}. Thus [[Randall]] suggests the spacecraft might encounter crème brûlée, and has therefore been equipped with a spoon for the purpose of collecting samples, as spoons are the traditional {{w|tableware}} provided for eating such desserts. Perhaps because the {{w|Cassini-Huygens}} probe, after landing on the surface of Saturn's moon Titan in January of 2005, found that ''its'' surface had what was described as [https://www.sciencenews.org/article/world-unveiled-cr%C3%A8me-br%C3%BBl%C3%A9e-titan a "crème brûlée" consistency], although there are significant differences between the two moons.

No such spoon is present on the ''Europa Clipper.''{{cn}} Its course is designed to avoid contact with Europa so as to prevent {{w|Planetary protection|contamination by microorganisms from Earth}}. The spacecraft is, however, equipped with a magnetometer at the end of a 8.5 meter deployable boom. Deployable instruments on spacecraft have often failed to deploy correctly, so the successful deployment of any instrument is considered a cause for celebration.

The title text expands on the joke by stating that the spacecraft "had BETTER" return samples of Europa to Earth. However, the ''Europa Clipper'' is not a {{w|sample-return mission}}.

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

:[A space probe with two rectangular solar panels, a circular dish of the front, and a very large spoon extending beneath, longer than the span of both solar panels]

:[Below the panel:]
:Good news: NASA's '''''Europa Clipper''''' is en route to Europa and has successfully deployed its crème brûlée spoon.

==Trivia==
The Clipper spacecraft was at one point to be developed alongside a lander, which was later dropped from being part of the same (or very closely partnered) mission. The latest version of the {{w|Europa Lander}} proposal is far behind the Clipper in implementation, not yet even being guaranteed funding.

Any actual sample return mission is currently far into the future of {{w|Ocean Worlds Exploration Program|the related plans for exploration}}, along with the possibility of digging deep enough into the ice to finally confirm or dismiss some of the more interesting theories about the world concerned.

In Arthur C Clarke's novel '''2010''', the monolith aliens tell humanity ''"All these worlds are yours - except Europa. Attempt no landing there."'' Contrary to the suggestion of the comic, no landing or any other physical interaction beyond observation of the surface of Europa is planned.

{{comic discussion}}
[[Category:Space]]
[[Category:Space probes]]
[[Category:Food]]

Talk:2626: d65536

2022-05-31T05:50:00Z

141.101.69.30:

I wonder: can we even make a fair polyhedron with 65536 faces? In Randal's illustration, the faces seem to be irregular hexagons. [[Special:Contributions/172.70.130.105|172.70.130.105]] 21:37, 30 May 2022 (UTC)
: This is better than my question, which was simply if you could tile a sphere with these. [[Special:Contributions/172.70.211.36|172.70.211.36]] 23:01, 30 May 2022 (UTC)
:Definitely possible, just create two identical right pyramids with a 32768-gon base and glue the bases together. [[User:Clam|Clam]] ([[User talk:Clam|talk]]) 23:53, 30 May 2022 (UTC)

I don't know why it's so big? Seems like it should have a diameter of approx. 1 meter. [[Special:Contributions/172.70.130.105|172.70.130.105]] 21:37, 30 May 2022 (UTC)

Should the title and picture file use "d" or the comic's difficult to type "ᴅ"?
[[User:While False|While False]] ([[User talk:While False|talk]]) 21:55, 30 May 2022 (UTC)
:Since xkcd uses small caps as lowercase letters, the "ᴅ" should just be considered xkcd-font for "d", and as such need not be used on the title, which is not using the xkcd font.

If you really did want to generate a 16 bit integer with physical dice, it would be much simpler to roll a [https://www.thediceshoponline.com/impact-opaque-hexidice-d16-hexadecimal-dice hex die] four times. [[User:Clayot|Clayot]] ([[User talk:Clayot|talk]]) 23:30, 30 May 2022 (UTC)
:Rolling a binary die 16 times would also work. You can get binary dice for 1¢ each. [[Special:Contributions/108.162.245.69|108.162.245.69]] 01:31, 31 May 2022 (UTC)

I think the hardest part (or maybe second-hardest part) is figuring out which facet is the one on top. [[Special:Contributions/162.158.78.109|162.158.78.109]] 00:46, 31 May 2022 (UTC)
:Roll it on a glass table, check from below which face it's landed on instead. Wait until it has settled safely, though, or it might land on ''your'' face! [[Special:Contributions/172.70.90.227|172.70.90.227]] 04:58, 31 May 2022 (UTC)

What material should it be to be light enough to easily roll it but cheap enough that doing the 1,5 meters doest cost a fortune ? Sorry if the question is not clear. [[Special:Contributions/141.101.69.30|141.101.69.30]] 05:50, 31 May 2022 (UTC)

831: Weather Radar

2022-05-21T00:23:45Z

141.101.69.30: Undo revision 272314 by Explain xkcd server admin (talk)

{{comic
| number = 831
| date = December 8, 2010
| title = Weather Radar
| image = weather_radar.png
| titletext = Ever notice how there aren't as many thunderstorms now as there were when you were a kid? Much like 'the shuffle on my MP3 player has a bias', this is occasionally true but universally believed. Brains are so interesting!
}}

==Explanation==
A {{w|weather radar}} is a device which uses the reflection of radio waves from rain or snow to detect where there is rainfall. The information from the radar is then shown on a map. In this case green means light rain while red or white represent very heavy rain - possibly a {{w|thunderstorm}}. These maps can be quite beautiful and mesmerizing to look at. In this case the speaker (who is located where the black dot is) enjoys watching interesting, unexpected events on the radar and is surprised to see a massive, unexpected storm heading straight for him. A storm indeed appears but splits in half and passes either side of him. The reaction of the speaker shows that this has happened before.

The caption suggests that this happens when the people who run the radar notice you looking at the page enough they tease you by adding a fake storm coming towards you which then disappears just as it approaches the speaker.

The title text explores how our perceptions are often inaccurate - someone may think that there are fewer storms than when they were young or that certain songs come up more often on their MP3 player, even when they don't. There are lots of these {{w|List of cognitive biases|types of biases in judgement}}.

==Transcript==
:[A black dot on a pixelated weather radar screen.]
:Sigh. Just a few clouds.

:[The clouds develop into orange, to the left of the dot.]
:Whoa! Huge storm out of nowhere!

:[The orange becomes red, and the storm moves towards the dot.]
:It's ''growing!'' And headed right for me! ''Awesome!''

:[The storm splits in half.]
:Hey! What's it...

:[The two halves of the storm pass by the dot.]
:Dammit! ''Again?!''

:When the folks at the weather offices see you refreshing the radar too often, they start teasing you.

{{comic discussion}}
[[Category:Comics with color]]
[[Category:Weather]]

455: Hats

2022-05-21T00:23:17Z

141.101.69.30: Undo revision 270760 by Explain xkcd server admin (talk)

{{comic
| number = 455
| date = July 28, 2008
| title = Hats
| image = hats.png
| titletext = ...
}}

==Explanation==
[[Black Hat]] encounters a person who is wearing not one, but two black hats. Black Hat is not a person to be trifled with, but from his reaction, he apparently believes that Two Black Hats represents a considerable danger to him. Black Hat knows how dangerous he is to those with one fewer black hat than him, so he continues the logic and realises that one who has one ''more'' black hat must be proportionally dangerous to him.

If a black hat is assumed to be akin to a badge of rank, then Two Black Hats certainly is superior to him in the capacity and willingness to do evil. Alternatively, and even more worrying, Two Black Hats could be someone who has the desire and the ability to acquire black hats (possibly killing the previous owners in the process if having two black hats really means that the individual is more malevolent than Black Hat), which he then wears like a badge of honor. With all this in mind, Black Hat edges away, keeping Two Black Hats in sight at all times.

This comic is also a metatextual joke about xkcd itself. Because of the comic's simplistic art style and characterization, Black Hat has only two defining physical traits: his hat and his hair, which we see when he takes off his hat, and one defining personality trait, his malevolence. Randall then implies that the two traits must be correlated, so that a black hat signifies malevolence, and accordingly two hats must signify even more malevolence -- an idea that wouldn't make any sense in real life, where a person with two hats would just be making an odd fashion choice.{{Citation needed}}

The title text is simply "..." This may represent the slow-motion pause during which Black Hat's nefarious life flashes before his eyes, as he considers his impending doom. It may also emphasize how the usually witty Black Hat is, for once, speechless. Or the title text is similar to that in [[412: Startled]], where Black Hat also becomes the little one (and with much focus on the black hat, as in this comic). As mentioned there, such a short title text could be due to the fact that it's a somewhat surreal comic, and any further commentary might have detrimentally brought it down to Earth. See also [[82: Frame]], with the same title text, but no relation to black hats.

Two Black Hats makes a reappearance in [[826: Guest Week: Zach Weiner (SMBC)]], down by the restrooms.

==Transcript==
:[Black Hat is walking.]

:[Black Hat stops in front of another man with two Black Hats, the uppermost hat tilted about 45 degrees back.]

:[After two panels, the original Black Hat steps backward, shuddering slightly.]

{{comic discussion}}
[[Category:Comics featuring Black Hat]]
[[Category:Characters with hats]]

2407: Depth and Breadth

2021-01-05T12:18:57Z

141.101.69.30: /* Explanation */ Dante's anniversary

{{comic
| number = 2407
| date = January 4, 2021
| title = Depth and Breadth
| image = depth_and_breadth2.png
| titletext = A death-first search is when you lose your keys and travel to the depths of hell to find them, and then if they're not there you start checking your coat pockets.
}}

==Explanation==
{{incomplete|Created by a LOAF OF BREAD. Please mention here why this explanation isn't complete. Do NOT delete this tag too soon.}}

{{w|Tree (data structure)|Tree structure}}s are one of the most common data structures used in computer science. The common ways of enumerating items arranged in a tree is either {{w|Depth-first search|depth-first}}, or {{w|Breadth-first search|breadth-first}}, which are depicted accurately in the comic. Randall humorously combines the words, to produce "brepth-first", "deadth-first", "bread-first", and "death-first" search algorithms.

Depth-first search explores down the full branches of the tree before exploring the higher levels of the tree. The "opposite" of this is breadth-first search, which explores each level of the tree at a time. This type of tree structure was already discussed as inefficient for human needs in [[761: DFS]].

In the "brepth-first" algorithm, a depth-first and a breadth-first search are hybridized where the left-most node is visited more frequently than the right node, but the right node is still visited. This might be good for exploring data that is loosely but not strictly weighted to the left, or where data in deeper nodes needs some time to be loaded before it can be used. As implied by [[761: DFS]], this might be the best algorithm for a human to employ, where one can be just as knowledgeable as needs be in just enough topics to hold conversation or be quick to act in case of danger during a date. Informed search algorithms like [https://en.wikipedia.org/wiki/A*_search_algorithm A* search], [https://en.wikipedia.org/wiki/Beam_search Beam search] and other [https://en.wikipedia.org/wiki/Best-first_search Best-first search] algorithms show this type of behavior by expanding the most ''promising'' node in the current set (under some appropriate metrics).

The nature of the "deadth-first" algorithm is unclear and inefficient, since it searches the same nodes multiple times before moving to an entirely different region of the tree. It might be useful in a context where examining nodes has some probability of returning a noisy or incorrect result, such as searching for small objects that may be overlooked.

The bread-first search is taken literally. Bread is searched for first. Since the computer user now has already met their want to find bread, the computer has no reason to explore the tree at all.

The title text introduces a "death-first" search, in which the user explores what it is like to be dead, before considering anything else. Specifically, the title text refers to hell, which calls to mind the adventures of Dante Alighieri in {{w|Inferno (Dante)| his ''Inferno''}}, and is a less likely place for keys to be left than one's coat pockets {{Citation needed}}. In 2021 (the year this comic was published) there are celebrations for the 700th anniversary of Dante's Death. Celebrations are expected to take place among the living only, and not in Hell.{{Citation needed}} A much more pleasant death-first algorithm might be to skip hell and purgatory and search heaven first, perhaps multiple times (which in itself would be a use of the deadth-first approach).

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

:[Five panels, each containing identical copies of what is approximately a balanced binary tree, greyed out in the background. The tree has a height of 3 and 15 nodes.]
:[In all five panels, a black twisty arrow in the foreground indicates the order in which nodes are traversed. The arrow does not complete the entire traversal but cuts off at a point. Backtracking is indicated with a dotted line.]
:[In the descriptions below, node 1 is the root, nodes 2 and 3 are its child nodes, nodes 4 and 5 are 2's child nodes, nodes 6 and 7 are 3's child nodes, nodes 8 and 9 are 4's child nodes, and so on up to node 15.]
:[Backtracking is omitted from the descriptions below, as they increased confusion when read.]

:Depth-first search
:[The arrow visits nodes 1, 2, 4, 8, 9, 5, 10, 11.]

:Breadth-first search
:[The arrow visits nodes 1, 2, 3, 4, 5, 7[''sic''], 6, 8.]

:Brepth-first search
:[The arrow visits nodes 1, 2, 4, 5, 8, 9, 3, 6, 10, 11.]

:Deadth-first search
:[The arrow visits nodes 1, 2, 4, 4, 2, 4, 3, 6, 12, 13, 12.]

:Bread-first search
:[The arrow starts at node 1, then leaves the tree off to the right to point to a loaf labeled "Bread".]

{{comic discussion}}
[[Category:Programming]]
[[Category:Food]]