explain xkcd - User contributions [en]

Talk:620: Wings

2025-07-24T04:03:13Z

Conjuncts: Commentary on belay equipment

Cueball's physics has a mistake on this one (or at least assumes we've managed to heat the atmosphere of Titan to Earth's temperature). The temperature of Titan is roughly 1/3 the temperature of Earth on an absolute scale. Starting with the Ideal Gas Law, PV = NkT (k is Boltzmann's constant, N is # of molecules, P is pressure, V is volume, T is temperature), its easy to define the density of a gas, ρ as:

ρ = m/V = (m P)/(N k T) = P (m/N) / (k T)

Titan's atmosphere is 98.4% molecular nitrogen (N2) and on Earth only 78.1% molecular nitrogen (by volume), but for simplicity we'll assume 100% for both. The weight of one molecule of Nitrogen is (m/N) ~ 2 × 14 × 1.67x10-27 (kg/molecule) (there are 28 nucleons per molecule with a mass of about 1.67x10^-27 kg.

The pressure on Titan is PTitan=146.7 kPa, and TTitan = 93.7 K, while on Earth PEarth=101.3 kPa and TEarth = 287 K.

Plugging in numbers, we get ρTitan = 5.3 kg/m3 and ρEarth = 1.2 kg/m3 (note the measured surface density of air on Earth is 1.2 kg/m3 at Earth's mean temperature even without the simplifying assumption of 100% N2).

Hence Titan's atmosphere is 4.4 = (5.3/1.2) times denser than Earth's (or 340% denser); not 50% denser as stated in the comic.

You will get the 50% denser if you assume the same planetary temperature on Titan as on Earth. Titan at 287 K would have a density of ρTitan at 287K ~ 1.73 kg/m3 which is about 50% greater than Earth's.

For the second calculation (panel 2), note {{w|Lift_(force)|lift}} is proportional to the density of air. If your action on Earth creates a lift of L0 and you weigh W0, on Titan you'd have a lift of 4.4 L0 (Cueball calculated 1.5 L0) due to the greater air density. Your weight would only be 0.14 W0, due to Titan's lower surface gravity. If lift balances weight, you would be able to fly on Titan, that is if 4.4 L0 = 0.14 W0. That means to fly on Titan you need a lift on Earth of L0 = 0.03 W0, that is 3% of your Earth weight. Substituting Cueball's Titan density you would get the critical value from the comic: L0 = 0.14 W0/(1.5) = 9% W0.

PS: I largely adapted this [http://forums.xkcd.com/viewtopic.php?f=7&t=43578&hilit=620+wings&start=120#p1726506 my writeup on xkcd forums from 2009 when the comic was made]. [[User:Jimbob|Jimbob]] ([[User talk:Jimbob|talk]]) 05:44, 8 June 2013 (UTC)
:That was the whole point of Blackhat's presence. He was there to make sure Rob (AKA Cueball) wasn't hurt.
:Fortunately, Blackhat couldn't care less about the outcome. So he's got that going for him, which is nice. [[User:Weatherlawyer| I used Google News BEFORE it was clickbait]] ([[User talk:Weatherlawyer|talk]]) 01:21, 29 January 2015 (UTC)

Why is this not a thing you can do in amusement parks or places like that?[[Special:Contributions/141.101.104.44|141.101.104.44]] 17:00, 8 September 2016 (UTC)

I think that the bridge to which Cueball attached his wings is inspiration for the bridge in [[Click and Drag]].--[[User:Obscure xkcd reference|Obscure xkcd reference]] ([[User talk:Obscure xkcd reference|talk]]) 13:47, 13 November 2021 (UTC)

Okay so maybe I just don't know enough about the physics, but... shouldn't the bricks be dangling? In the illustration, it looks like the rope should have a little slack in it. With nothing keeping it taught, I don't see how it would cancel out any of a person's weight. It also seems like you'd have to account for the friction of the pulleys, which I think would both increase the force required to get off the ground and slow the fall back down. Idk maybe I'm just overthinking this. [[Special:Contributions/172.70.111.34|172.70.111.34]] 16:18, 5 October 2024 (UTC)

:I agree completely. [[User:Conjuncts|Conjuncts]] ([[User talk:Conjuncts|talk]]) 04:03, 24 July 2025 (UTC)

It occurred to me that you could probably recreate this safely using rock climbing/belay equipment. Clip the flyer into the pulley system; on the other end, set up a harness weighing 91% that person's body weight. Also clip the harness to an active belayer. The belayer's job is to keep the rope only slightly slack, in case of sudden falls. However, you'll need to find a pulley with sufficiently low friction (although that problem is also present in Randall's original setup.) [[User:Conjuncts|Conjuncts]] ([[User talk:Conjuncts|talk]]) 04:03, 24 July 2025 (UTC)

1987: Python Environment

2025-07-08T17:13:14Z

Conjuncts: Recommend modern python environment managers such as uv

{{comic
| number = 1987
| date = April 30, 2018
| title = Python Environment
| image = python_environment.png
| titletext = The Python environmental protection agency wants to seal it in a cement chamber, with pictorial messages to future civilizations warning them about the danger of using sudo to install random Python packages.
}}

==Explanation==
A development environment is the collection of tools used to create a computer program. It generally includes an {{w|Interpreter_(programming)|interpreter}}, a {{w|package manager}}, and various {{w|Library_(computing)|libraries}} that the project needs. One such example is {{w|Python_(programming_language)|Python}}.

Historically, a computer would have only a single such environment, ie. only one copy of these tools installed, with all programs running off of it. However, people quickly discovered that this caused issues when said tools got updated and unintentionally break the programs. As an example, many programs still run on Python 2.7 (released in 2010) because Python 3.x changed things around so much that the effort to alter the program to run on it was deemed too much effort.

In an attempt to solve the above issue, the solution was determined to simply have each program have their own copy of the tools that they could be free to modify however they like without worrying about how it might affect other programs. Multiple tools were then developed intending to make it easier for a user to manage and keep track of the now-multiple environments, but it seems that for Randall this has simply created a new issue: he has lost track of which copy of Python his computer uses by default.

To avoid the chaos described in the comic, modern Python recommends the consistent use of a package manager like [https://github.com/astral-sh/uv uv], [https://github.com/python-poetry/poetry Poetry], or [https://docs.python.org/3/library/venv.html venv] to isolate Python environments and versions.

{{w|Superfund}} is a US federal government program created for cleaning up contaminated land. The comic is saying that his computer's Python environment is so messed up that it's comparable to a real-world environmental disaster.

The title text may refer to the philosophical debate surrounding the construction of warning features around the [[wikipedia:Waste_Isolation_Pilot_Plant#Warning_messages_for_future_humans|WIPP]] site in New Mexico, and other nuclear waste disposal sites. In particular, it may refer to [https://web.archive.org/web/20090320054657/http://www.wipp.energy.gov/picsprog/articles/wipp%20exhibit%20message%20to%2012,000%20a_d.htm this article]. These would have to last and be understandable for tens of thousands of years, longer than any known human-made structure or language to date. It also refers to the use of "sudo", a command utility included in many Linux distributions that allows a user to operate with heightened permissions. Using "sudo" to install a Python package may make the package available to the entire system, or, based on the settings of Virtualenv/Anaconda, it may end up installing the package in a user's home directory. This would make it so that the user could not update, edit, or remove the packages.

;$PATH
:$PATH refers to the {{w|PATH (variable)|PATH}} environment variable, which determines where to search for executable files. In this case, it indicates that the pip, Homebrew Python (2.7), and macOS's pre-installed Python are accessible on path, with ~/newenv/ and a mysterious ???? as part of PATH.
;pip
:{{w|pip (package manager)|pip}} is the Python {{w|package management system}}, and is used to install and manage python packages. As it is written in Python, it requires Python to run. It leads to easy_install, Homebrew Python (2.7), "(misc folders owned by root)", and ????.
;Homebrew Python (2.7)
:{{w|Homebrew (package management software)|Homebrew}} is a third-party macOS package manager. Homebrew Python (2.7) is the Python 2 version installed through Homebrew. This leads to Python.org binary (2.6) and /usr/local/Cellar.
;OS Python
:Apple bundles an (out of date) version of Python with macOS. This only leads to ????.
;????
:With so many versions of Python installed and used in the system, it becomes very hard to track which Python program uses which version and environment. The system becomes unpredictable and its workings and faults mysterious. All parts of the graph that lead to this point, lead to confusion.
;easy_install
:easy_install, much like pip, is a cpan-like tool to download and install Python packages. As of the creation of the comic, many people discourage its use. (e.g., [https://stackoverflow.com/questions/3220404/why-use-pip-over-easy-install this question on stack exchange.])
;Anaconda Python
:{{w|Anaconda (Python distribution)|Anaconda}} is a Python distribution for data science and machine learning-related applications.
;Homebrew Python (3.6)
:As of the creation of the comic, Python 3.6 is the current stable version of Python. It can be installed together with Python 2.7 on the same computer. Care must be taken to use an appropriate version for every Python program, however. Homebrew is a "macos" package management utility. Presumably, Randall installed Python 3.6 with Homebrew (as opposed to downloading and compiling the language himself).
;Python.org binary (2.6)
:[http://python.org Python.org] is the home site of the {{w|Python_(programming_language)|Python language}} and provides its reference implementation. Among other stuff, there are downloadable installers that create ready-to-use Python environments for you (on Windows and macOS only). It makes little sense, however, to use it on a computer where Homebrew, Anaconda, and a locally compiled version are already present, since the Python.org version is the baseline one, doesn't give you any benefits, and can't be optimized for your needs. Having an obsolete 2.6 version, when the typically used 2.7 is already on the computer, also doesn't help. Some justified uses do exist (tests, programs that depend on this particular version), but in the end, an extra version of Python just adds to the overall confusion.
;(Misc folders owned by root)
:This suggests that over years [[Randall]] dropped various versions of {{w|Python_(programming_language)|Python}} environments everywhere around his computer, probably by hand without proper installers, and used root privileges to do so. The exact locations either are highly nonstandard, so it makes no sense to show them to us, or have simply been forgotten. Now it's hard to even tell where exactly those Pythons lay, what in the system depends on them, and if it's safe to remove them or not (because if installed by the root, they can integrate into unexpected places in the system; having them can break something, and removing them can break something).
;<code>/usr/local/Cellar</code>
:The default (normal) location of the {{w|Homebrew (package management software)|Homebrew}} Cellar, the directory where Homebrew actually stores the files of the installed packages. It's a storage-only location, the files, including Python, will be symlinked from other, more convenient places in the files tree, and should not be used through /usr/local/Cellar path directly. It seems that Randall broke this safety rule in the past, so some stuff of his accesses Python directly in the Cellar. Such setup can break if Homebrew performs automatic maintenance in the Cellar (like removing unneeded versions of the packages). The name cellar is likely a reference to the practice of storing wines and other alcohol in cellars, intended as a pun of homebrew.
;<code>/usr/local/opt</code>
:A folder that is usually created by Homebrew.
;/(A bunch of paths with "Frameworks" in them somewhere)/
:Python on macOS is often distributed as a framework and placed in a "Frameworks" folder. For example, the system-included Python distribution in macOS resides in /System/Library/Frameworks, and many package managers will also install the framework in a folder with this name.
;$PYTHONPATH
:The environment variable PYTHONPATH specifies the search path for Python modules to the Python interpreter. Having it refer to locations controlled by 3 different package managers, each of which is managing software for different versions of Python, as shown, is likely to lead to incompatible software being loaded together.
;Another pip??
:Pip is a {{w|Recursive acronym}} for "Pip Installs Packages." There should only be one installation of pip (or other package management system) managing any given working environment. Often, additional "pip" executables are installed based on the Anaconda settings for different virtual envs. This often leads to internal contradictions in the software. Randall is confused as to how this other one relates to the rest of the development environments.
;~/python/
:Might be another virtualenv, or, given the absurdity of the rest of the comic, even a manually compiled python installation (many online guides instruct users to extract sources into the home (~) directory).
;~/newenv/
:Probably a virtualenv. Virtualenvs are mechanisms for having Python environments that don't conflict with the system Python. They include the Python interpreter, independent library paths, and usually a copy of pip. The user typically installs packages using the virtualenv's pip such that they can only be accessed by the virtualenv's Python instances, while more common packages are still referenced via the system Python paths.
;/usr/local/lib/python3.6
:The default place under a Unix-like OS for the Python 3.6 standard libraries for a locally compiled Python 3.6 interpreter.
;/usr/local/lib/python2.7
:The default place under a Unix-like OS for the Python 2.7 standard libraries for a locally compiled Python 2.7 interpreter.

==Transcript==
:[A single frame depicting a flowchart is shown. Many chaotic arrows are arranged between the items which are:]
:$PYTHONPATH
:EASY_INSTALL
:ANACONDA PYTHON
:HOMEBREW PYTHON (3.6)
:ANOTHER PIP??
:HOMEBREW PYTHON (2.7)
:PYTHON.ORG BINARY (2.6)
:PIP
:EASY_INSTALL
:$PATH
:(MISC FOLDERS OWNED BY ROOT)
:????

:[The endpoints are:]
:/usr/local/Cellar
:/usr/local/opt
:/(A BUNCH OF PATHS WITH "FRAMEWORKS" IN THEM SOMEWHERE)/
:~/python/
:~/newenv/
:/usr/local/lib/python3.6
:/usr/local/lib/python2.7

:[Caption below the panel:]
:My Python environment has become so degraded that my laptop has been declared a superfund site.

== Trivia ==

* A similar comic is {{xkcd|1654}} which is the same but for multiple languages.

{{comic discussion}}

[[Category:Computers]]
[[Category:Programming]]
[[Category:Flowcharts]]

Talk:Header text

2025-06-09T02:45:16Z

Conjuncts: Comprehensive list of comic-specific news

;Localized versions

Currently to me the header text is in German (as I live in Germany):
:Triff Randall Munroe in Berlin am 15. Oktober 2019!
:Hier die deutsche Ausgabe vorbestellen!
(Meet Randall Munroe in Berlin on 15th of October 2019! Preorder the german version here) where "Hier" (here) is a link.
4 odd things I noticed about this:
*It mentions the German version, but not the German verison of what. The book isn't even mentioned.
*When I (re)load the page, for a moment I get the image about winning a stick-figure-sketch of myself.
*XKCD does not use means like other pages (e.g. [[713: GeoIP]] to identify my language. As I am using a swedish VPN, I usually get advertisements in swedish (and redirections to swedish homepages, etc.). Maybe it is my browser settings which are set to German. Can someone identify the method used?
*The link leads to "https://www.xkcd.com/%22https://www.randomhouse.de/Buch/HOW-TO-Wie-man-s-hinkriegt/Randall-Munroe/Penguin/e547637.rhd?utm_source=autorenblog&utm_medium=banner&utm_campaign=how_to\%22" - a 404 page. (getting rid of the part before the 2nd https gets you to the page of the german publisher.
Someone got an idea on how to put this into the wiki properly? Are there other language versions as well? --[[User:Lupo|Lupo]] ([[User talk:Lupo|talk]]) 06:38, 16 August 2019 (UTC)

Yeah there is, in the UK the text changes to "I'll be coming to the UK for [https://xkcd.com/how-to/#tourdates the book tour]." There is Javascript in the page which sends a request to https://c.xkcd.com/how-to/news which is simply redirected (for me to https://xkcd.com/ukNews ) presumably based on GeoIP, definitely not a browser locale setting. Not sure how you would get them all, maybe iterate country codes through the start of the URL? I tried deNews which worked. [[Special:Contributions/162.158.34.172|162.158.34.172]] 17:57, 30 August 2019 (UTC)

;Black lives matter

As a note to whoever archieves this (I don't have the time to do it properly myself right now), today I noticed the first time, that the header text, which I think was empty recently changed to a cueball stating "black lives matter" and a link "how to help" to joincampaignzero.org. It might have been up for a few days. --[[User:Lupo|Lupo]] ([[User talk:Lupo|talk]]) 06:48, 4 June 2020 (UTC)

{{done}}; sorry I didn't notice your post here on the talk page before adding it. It seems like we should feature this article page more prominently somehow so people become aware of it. I'm not sure how that should be accomplished. [[User:JohnHawkinson|JohnHawkinson]] ([[User talk:JohnHawkinson|talk]]) 19:00, 9 June 2020 (UTC)
:No need to be sorry. I could've done it myself, but there seems to be (as you mention in the post below) a quite formal structure to the page, and currently I don't find the time to spend as much time on this wiki as I used to, so instead I just thought I'd put together a note, in case it is noticed in the future, to then have a rough starting date.--[[User:Lupo|Lupo]] ([[User talk:Lupo|talk]]) 06:01, 10 June 2020 (UTC)

;Formatting this page as a visual gallery?

It seems like there would be a lot of value in having this page as a visual archive of all of the header illustrations, not merely reducing them to plain text. Is there a reason that approach was not chosen, and are there any thoughts about how best to format and manage it? [[User:JohnHawkinson|JohnHawkinson]] ([[User talk:JohnHawkinson|talk]]) 19:01, 9 June 2020 (UTC)
:I guess it is because it is a much larger task to include all those images. But feel free to begin. I have created most of he text on this page, so I have already used a lot of time. There are links to the web archive where they can be seen. This was seen by me as a transcript of these, so it is possible to search for text bites. It will be a very long page to load if you include pictures directly here as well. But a link to the images placed in another page could be a possibility. --[[User:Kynde|Kynde]] ([[User talk:Kynde|talk]]) 07:53, 20 July 2020 (UTC)

;Recent BLM edits

I disagree with most of [[:User:Kynde]]'s [https://www.explainxkcd.com/wiki/index.php?title=xkcd_Header_text&oldid=194829 edits] from just now:
* Links to "Black Lives Matter" should remain to the url https://blacklivesmatter.com/ rather than hiding it behind an anchor, as [https://blacklivesmatter.com/ Black Lives Matter], because "Black Lives Matter" is not a clear unambiguous entity, and where the point is to show the URL, we should do so.
* That necessarily implies https://joincampaignzero.org should get the same treatment.
* By removing the June 17 section and combining into the June 3 section, it makes no sense to now say "The link goes to" and list where it went on June 3–16 but went elsewhere from June 17–present.
* "Fill it in when it changes" just looks bad. It is a comment to editors, not readers, and the wiki is for readers. It should be deleted or restored to a comment.

I would make all of these changes, but they have the appearance of edit warring, so I wanted to raise them here first. Thank you. [[User:JohnHawkinson|JohnHawkinson]] ([[User talk:JohnHawkinson|talk]]) 18:02, 18 July 2020 (UTC)
:I just tried to use the same format I have used on all the other changes to header texts over the last couple of years. I have also inserted link like this before. I can see this matter is much more sensitive than any previously used in the header (or at least where any noticed this page.). If you feel strongly about this, then please feel free to change it back, or change my edits somehow. I would prefer this entry does not diverge from the format of all the others, but since this header means a lot to many people, I will not change it back if you think it should be formatted differently than the rest. If you really wish, undo my changes, I will not redo them then. But I think this is just the same header, with a new link and thus did not warrant a new entry. I have done similar with other headers where just a small thing changes (yes I know the link is the important part here, and thus not a small change, but it did not change the header text or image!) --[[User:Kynde|Kynde]] ([[User talk:Kynde|talk]]) 07:57, 20 July 2020 (UTC)

;Ideas about the Jan 31, 2022 countdown?
It seems like the countdown's code is on github: https://github.com/munvoseli/xkcd-countdown
I can't seem to find any hints there what it's about, though.
--[[Special:Contributions/162.158.159.29|162.158.159.29]] 13:01, 11 January 2022 (UTC)
Nevermind, that's just the code of a progress tracker at https://munvoseli.github.io/xkcd-countdown/ .
--[[Special:Contributions/172.70.90.173|172.70.90.173]] 13:19, 11 January 2022 (UTC)

;1047

Comic 1047 (Approximations) has unique header text. [[Special:Contributions/172.70.110.245|172.70.110.245]] 16:12, 31 January 2022 (UTC)

;Comic-specific section incomplete

The section on comic-specific headers seems to be missing many examples. I found quite a few from just a couple minutes of browsing random comics (405, 432, 433, 826, 896), so I suspect a thorough search would turn up a lot more. [[Special:Contributions/162.158.146.136|162.158.146.136]] 15:21, 3 July 2023 (UTC)
:Unfortunately you're right. This page needs much more attention, I added an incomplete tag. --[[User:FaviFake|FaviFake]] ([[User talk:FaviFake|talk]]) 21:31, 3 July 2023 (UTC)

After crawling the API, I have what I believe is a comprehensive [https://gist.github.com/conjuncts/22e5da17266031775f93336f041456b3 gist] of comic-specific headers. I think this could be turned into a category? [[User:Conjuncts|Conjuncts]] ([[User talk:Conjuncts|talk]]) 02:45, 9 June 2025 (UTC)

;Missing "A Smarter Planet comics unique header text

The [https://web.archive.org/web/20190102070937/https://xkcd.com/asmarterplanet archived page of xkcd.com/asmarterplanet] shows this header text: "Bonus xkcd comics done for IBM's "[http://asmarterplanet.com/ A Smarter Planet]" initiative.", and it's missing fromt the page --[[User:FaviFake|FaviFake]] ([[User talk:FaviFake|talk]]) 09:10, 18 August 2023 (UTC)

;Word salad
This sentence in the header is not comprehensible: "In recent times there has been very long between the old go to text has been used for extended periods though." I'm not actually sure enough what it means to correct it. [[User:Nitpicking|Nitpicking]] ([[User talk:Nitpicking|talk]]) 14:15, 18 November 2024 (UTC)
:I'm guessing something like "In recent times there has '''not''' been very long between '''changes. T'''he old go'''-'''to text has been used for extended periods''',''' though."
:i.e., there have been rapid turn-arounds (to a topical update, then back to 'normal'). But, more time than not, it tends to sit on a more general non-topical message.
:I've not actually checked if this is true, or what edits might have been incrementally made to saladise the words that are there. [[Special:Contributions/172.69.195.200|172.69.195.200]] 15:33, 18 November 2024 (UTC)