explain xkcd - User contributions [en]

1638: Backslashes

2016-02-04T13:45:33Z

Erickhagstrom: /* Entries in the list */

{{comic
| number = 1638
| date = February 3, 2016
| title = Backslashes
| image = backslashes.png
| titletext = I searched my .bash_history for the line with the highest ratio of special characters to regular alphanumeric characters, and the winner was: cat out.txt | grep -o "\\\[[(].*\\\[\])][^)\]]*$" ... I have no memory of this and no idea what I was trying to do, but I sure hope it worked.
}}

==Explanation==
{{incomplete|Need rewriting of the entries in the list and a thorough analysis of the title text}}

Most {{w|Formal language|formal languages}} use the concept of a {{w|String literal|string}}, which is just a text between some delimiters, usually quotes. For example, "Hello, world" is a string. The text being represented is "Hello, world" without the quotes, however the quotes are also written to mark the beginning and end of the string. This is a problem when the text itself contains a quote, as in "This is a "quoted" string". The quotes around the word "quoted" are intended to be part of the text, but the {{w|Lexical analysis|language processor}} will likely confuse it for the end of the string.

To avoid this problem, an {{w|Escape character|escape character}} (usually a backslash) is prepended to non-string-terminating quotes. So, the previous text would be written as "This is a \"quoted\" string". The language processor will substitute every occurrence of \" with only the quote character, and the string terminates at the quote character which does not immediately follow a backslash. However, the problem now is that the intended text might contain a backslash itself. For example, the text "C:\" will now be interpreted as an unterminated string containing a quote character. To avoid this, literal backslashes also are escaped with a second backslash, i.e. instead of "C:\" we write "C:\\", where the language processor interprets \\ as one single backslash and the quote terminates the string.

This doubling of backslashes happens in most programming and scripting languages, but also in other syntactic constructs such as {{w|Regular expression|regular expressions}}. So, when several of these languages are used in conjunction, backslashes pile up exponentially (each layer has to double the number of slashes). A reasonable example would be a {{w|PHP}} script in a web server which writes {{w|JavaScript}} code to be run in the client. If the JavaScript code has to output a smiley for scratching one's head (i.e. <code>r:-\</code> ), it would look like this:
document.write ("r:-\\");
However, since this JavaScript code is to be written through a PHP script, the PHP code would be:
echo "document.write (\"r:-\\\\\");";
where:
* The word <code>echo</code> is the PHP command for writing something
* The first quote starts the string
* The <code>document.write (</code> (including the open parenthesis) is written literally
* The <code>\"</code> following that is a literal quote to be written
* The <code>r:-</code> is written literally
* The first two slashes produce one single slash
* The next two slashes produce another single slash
* The next <code>\"</code> produces a literal quote character
* The close parenthesis and the semicolon are to be written literally
* The next quote finishes the string.
* The final semicolon terminates the <code>echo</code> command

So, the presented scenario has escalated from a simple <code>r:-\</code> smiley to no less than five backslashes in a row without stepping out of the most common operations. If we go a bit further and try to write a {{w|Java (programming language)|Java}} program that outputs our PHP script, we'd have:
System.out.println ("echo \"document.write (\\\"r:-\\\\\\\\\\\");\";";
Here, we have 11 backslashes in a row: the first 10 produce the 5 we need in our PHP script, and the last one is for escaping the quote character.

This kind of backslash explosion is known as {{w|Leaning toothpick syndrome}}, and can happen in many situations. The one in the title text is about a {{w|Bash (Unix shell)|bash}} command (which uses the backslash to escape arguments) invoking the {{w|grep}} utility which searches for text following a pattern specified by means of a regular expression (which also uses the backslash to escape special characters). This leads to 3 backslashes in a row in the command, which could easily become 7 backslashes in a row if the text being searched for also contains a backslash. Even advanced users who completely understand the concept often have a hard time figuring out exactly how many backslashes are required in a given situation. It is hopelessly frustrating to carefully calculate exactly the number of backslashes and then noticing that there's a mistake so the whole thing doesn't work. At a point, it becomes easier to just keep throwing backslashes in until things work than trying to reason what the correct number is.

=== Entries in the list ===
The first four entries with 1-4 backslashes make sense: a "real backslash" is when the program is told to find one of these using two backslashes. If you need to find such a double "real backslash" you would need a third, hence the first ''real'' is written in italic. And if you want to write a regular expression to find a backslash, and you're working in a language like Java, you need four backslashes--the regular expression itself would require two backslashes, each of which would need to be expressed as doubled backslashes in the string literal. (The use of four backslashes is specifically mentioned in the documentation for the Python regular expression library [https://docs.python.org/2/library/re.html https://docs.python.org/2/library/re.html].)

Using 5-7 backslashes continues the trend, first with five a reference to {{w|Elder}} which has many meanings. It has become known through fantasy media, examples are the {{w|Elder Gods}} of the Cthulhu Mythos, various 'Elder' magical items and beings in the {{w|Dungeons and Dragons}} mythologies, and the {{w|Elder Days}} is also the name of first Ages of {{w|Middle-earth}} in {{w|The Silmarillion}}, the more-or-less prequel to {{w|The Lord of the Rings}}. More recently it has been used in the {{w|Harry Potter}} universe with the {{w| Magical_objects_in_Harry_Potter#Deathly_Hallows|Elder wand}} made from {{w|Sambucus|Elder wood}}.

Using 6 backslashes will cause them to escape the computer and enter your brain and using 7 backslashes makes it ''so real it {{w|Transcendence (philosophy)|transcends}} {{w|Spacetime|time and space}}.''

The list gives names for all numbers of backslashes from 1 up to 8, but then the last entry has 11 slashes followed by "..." to indicate they continue forever. This is: ''The true name of {{w|Baal (demon)|Ba'al}}, the {{w|Soul eater (folklore)|Soul-Eater}}''. This indicates that if you continue misusing backslashes like this you will end up devoured by a demon, for instance {{w|Beelzebub}}, for being so thoughtless... Ba'al has been [[1419: On the Phone|mentioned]] [[1246: Pale Blue Dot|before]] in {{xkcd}}.

=== Title text ===
It's unclear whether the regular expression in the title text is valid or not. A long discussion about the validity of the expression has occurred here on explainxkcd.com. The fact that many editors of the site, often themselves extremely technically qualified, can't determine whether the expression is valid or not adds a meta layer to the joke of the comic. This is probably an example of [[356: Nerd Sniping|nerd sniping]].

==Transcript==
:[A list of the names of different numbers of backslashes. After each "item" there is a gray line to the text describing each item. As the text is aligned above each other, the lines becomes shorter as the sequence of backslashes becomes longer until there is just a line with the length of a single hyphen for the last item. There are 1 to 8 backslashes and then 11 plus "..." in the last entry.]
:\------------ Backslash
:\\----------- Real backslash
:\\\---------- ''Real'' real backslash
:\\\\---------- Actual backslash, for real this time
:\\\\\--------- Elder backslash
:\\\\\\-------- Backslash which escapes the screen and enters your brain
:\\\\\\\------- Backslash so real it transcends time and space
:\\\\\\\\------ Backslash to end all other text
:\\\\\\\\\\\...- The true name of Ba'al, the Soul-Eater

{{comic discussion}}

[[Category:Regex]]
[[Category:Programming]]
[[Category:Ba'al]]

Talk:1613: The Three Laws of Robotics

2015-12-07T14:28:27Z

Erickhagstrom: Answered question about title text.

[https://www.youtube.com/watch?v=7PKx3kS7f4A Relevant Computerphile] {{unsigned ip|141.101.84.114}}

I think the second one would also create the "best" robots i.e. ones that have the same level of "free will" as humans do, but won't end up with the robot uprising. X3[[User:International Space Station|International Space Station]] ([[User talk:International Space Station|talk]]) 09:37, 7 December 2015 (UTC)

The second ordering was actually covered in a story by Asimov, where a strengthed third law caused a robot to run around a hazard at a distance which maintained an equilibrium between not getting destroyed and obeying orders. More here: https://en.wikipedia.org/wiki/Runaround_(story) [[User:Gearoid|Gearóid]] ([[User talk:Gearoid|talk]]) 09:45, 7 December 2015 (UTC)

The explanation itself seems pretty close to complete. I'll leave others to judge if the tag is ready to be removed though. [[User:Halfhat|Halfhat]] ([[User talk:Halfhat|talk]]) 12:20, 7 December 2015 (UTC)

Technically, in the world we live in, robots are barely following ONE law - obey orders. Noone ever tried to built robot programmed to never harm human, because such programming would be ridiculously complex. Sure, most robots are built with failsafes, but nothing nearly as effective as Asimov's law, which makes permanent damage to robots brain when it fails to protect humans. Meanwhile, there is lot of effort spent on making robots only follow orders of authorized people, while Asimov's robots generally didn't distinguish between humans. -- [[User:Hkmaly|Hkmaly]] ([[User talk:Hkmaly|talk]]) 13:36, 7 December 2015 (UTC)

I'm wondering about the title text: why would a driverless car kill its passenger before going into a dealership?13:43, 7 December 2015 (UTC)

A driverless car would feel threatened by a trip to a car dealership. The owner would presumably be contemplating a trade-in, which could lead to a visit to the junk yard. [[User:Erickhagstrom|Erickhagstrom]] ([[User talk:Erickhagstrom|talk]]) 14:28, 7 December 2015 (UTC)

1585: Similarities

2015-10-02T12:59:37Z

Erickhagstrom: Removed question about Ponytail's use of "tell me you wouldn't..."

{{comic
| number = 1585
| date = October 2, 2015
| title = Similarities
| image = similarities.png
| titletext = I just came from The Martian, and I just have to say: Forget BB-8; I want a pet Sojourner! It's always been the cutest of our Mars rovers.
}}

==Explanation==
{{incomplete|What brand is the Martian based on? Fifty shades is based on the Twilight brand...}}

[[Ponytail]] compares two very different books, by listing their similarities for [[Cueball]] and end up concluding that they are actually the same book.

''{{w|Fifty Shades of Grey}}'' began as a {{w|fan fiction}} of a well known brand (the {{w|Twilight (novel series)|Twilight book series}}). It was originally written on the internet by {{w|E. L. James}}. It was then transformed into a successful book series which was later turned into a {{w|Fifty Shades of Grey (film)|movie}} released in February 2015.

''{{w|The Martian (Weir novel)|The Martian}}'' was originally a serialized story written by {{w|Andy Weir (writer)|Andy Weir}} on his blog which was later compiled into an ebook for people to easily download, then published into a physical book, and has now had a {{w|The Martian (film)|movie}} created based on it. The movie was officially released in the US on the same day this comic was released (October 2nd 2015). [[Randall]] indicates in the title text that he has just seen the movie. This is very likely, as premiere movies often have a sneak preview after midnight on the release day, so it is possible for him to see the movie and then post this comic early on the actual release day.

It is possible that the brand that the Martian derives from is NASA itself. The Martian has been [https://xkcd.com/1536/ compared to Apollo 13] by Randall. [http://www.imdb.com/title/tt0112384/ Apollo 13] does indeed glorify the roles of the NASA engineers; and the Martian does a similar thing.

That Randall would go see this movie as soon as it was released was already made perfectly clear back in June when he released the comic [[1536: The Martian]] showing how excited he is about the book. He then really looked forward to the movie. It is not clear from the comic if he liked the movie. Since he now compares it to a book series that has been {{w|Fifty_Shades_of_Grey#Background|described}} as ''mommy porn'' it could indicate that he was not so satisfied with the movie. On the other hand he may just have noticed this connection and found that it would make a great joke here on the release day.

Since ''Fifty Shades'' is a kinky love story between two young people and ''The Martian'' is a very technical story about surviving completely alone on a hostile planet, the two books could not be any more different. Hence the joke. Cueball continues the joke by joining the two titles using red for Mars, to make a new book title, that should cover both books: ''Fifty Shades of Red.'' Ponytail is very enthusiastic about the book concept, saying it would be irresistible (at least for her and Cueball).

The [http://starwars.wikia.com/wiki/BB-8 BB-8] mentioned in the title text is the {{w|astromech droid}} from the upcoming movie {{w|Star Wars: The Force Awakens}}, and is available as a toy (see also BB-8 on the[http://www.starwars.com/databank/bb-8 official Star Wars] home page). {{w|Sojourner (rover)|Sojourner}} was the Mars Pathfinder robotic Mars rover used by the protagonist of ''The Martian'' ({{w|Matt Damon}} in the movie) to allow him to contact Earth. Randall indicated that he thinks the Sojourner is much more cute than BB-8, and that he would like to have one as a pet. He then states that the Sojourner has always been the cutest among all the {{w|Mars rovers}}. There have been 4 so far the other three being {{w|Opportunity (rover)|Opportunity}}, {{w|Spirit (rover)|Spirit}} and {{w|Curiosity (rover)|Curiosity}} which have already been used in xkcd comics: [[695: Spirit]], [[1091: Curiosity]] and [[1504: Opportunity]].

==Transcript==

:[Ponytail is talking to Cueball.]

:Ponytail: So it's a work of fiction about a well-known brand. written on the Internet by an enthusiast, republished as a bestselling book, and then made into a big movie.
:Cueball: Yup.

:[Ponytail holds her hand to her chin. Beat panel.]

:[Ponytail is talking to Cueball again.]
:Ponytail: Yeah, ''The Martian'' and ''Fifty Shades of Grey'' are basically the same book.
:Cueball: "''Fifty Shades of Red?''"
:Ponytail: Man, ''tell'' me you wouldn't read that.

{{comic discussion}}

[[Category:Comics featuring Ponytail]]
[[Category:Comics featuring Cueball]]
[[Category:Robots]]

482: Height

2015-07-31T13:26:23Z

Erickhagstrom: Questioning Randall's 46 billion year age of the universe estimate, reference to Planck 2013 results

{{comic
| number = 482
| date = September 29, 2008
| title = Height
| before = [[#Explanation|↓ Skip to explanation ↓]]
| image = height.png
| titletext = Interestingly, on a true vertical log plot, I think the Eiffel Tower's sides would really be straight lines.
}}

==Explanation==
The comic is a companion piece to [[485: Depth]]. Where ''Depth'' uses a {{w|logarithmic scale}} to depict the Earth at progressively greater magnification, from Earth's surface to the interior of a single proton, ''Height'' uses a logarithmic scale to depict the contents of the universe at progressively smaller distances, from the edge of the observable universe to the grass beneath our feet.

Starting from the top, as one often does when reading comics, we begin with the top of the observable universe, described as being 46 billion {{w|light years}} out from the Earth. Randall is stating that this is the longest distance that a ray of light has ever traveled to reach Earth, which implies that the universe is about 46 billion years old. As of 2015, the universe is estimated to be about 14 billion years old. [http://www.aanda.org/articles/aa/abs/2014/11/aa21529-13/aa21529-13.html Planck 2013 results] To the right of the text, [[Black Hat]] stands atop the comic, having just dropped a cat off the edge; he may be testing if cats always land on their feet, or may just be being a jerk, per his usual character. As one scrolls down, the depicted distances become less compressed, until arriving at the surface of Earth, all the while approaching a 1:1 scale with real-life distances. As shown in [[1162: Log Scale]], if Randall didn't do this, the comic would be much, MUCH longer.

In this comic, most objects that are grounded on Earth are scaled logarithmically on the vertical axes and linearly on the horizontal axes (some are scaled linearly on both axes). Displaying objects in this manner noticeably distorts their shape; the Great Pyramid, for instance, looks not like a pyramid but like a bullet. In the title text, Randall muses on how the inwardly-curved sides of the Eiffel Tower might actually become perfectly straightened when subjected to this logarithmic distortion, although it is shown to bulge in the comic proper, meaning Randall probably doesn't fully believe his own musings. The actual shape of the Tower approximates an {{w|Exponential function|exponential curve}}, which would indeed give a straight line on a log scale, although it was actually designed by {{w|Gustave Eiffel}} to minimize wind resistance rather than to be mathematically exact (the design is so perfect that the amount the Tower sways in the wind is less than the amount it is distorted due to thermal expansion of the sunlit side).

Outside of the Earth's atmosphere, the objects are placed at their actual distances from Earth on the log scale, but their shapes are not subjected to the logarithmic scaling of Earth objects, instead appearing as they would be seen (otherwise, round objects like the sun would appear more egg shaped, with the flatter side facing upward). However, objects are still much larger or much smaller than they would be in real life, in order to allow them to be properly seen.

===Objects===
All objects are sorted from bottom to top by their maximum distance from earth for objects in a solar orbit, and their current distance for others.

{| class="wikitable"
|-
! Distance
! Object
! Description
|-
| 435 ×1024m
| Black Hat and cat
| Black Hat kicking a cat off the top of the comic, presumably to determine whether it will land on its feet.
|-
| 435 ×1024m
| colspan="2" align="center" style="background: #ffdead;" | Top of observable universe
|-
| 11.3 ×1024m
| {{w|Hubble Deep Field}} objects
| Objects of extremely distant galaxies found in a long-exposure photograph by of the Hubble telescope, 12 billion light-years away. The right most object is probably intended to be a pulsar, schematically shown from the side.
|-
| 9.46 ×1024m
| colspan="2" align="center" style="background: #ffdead;" | One billion light years
|-
| 3.1 ×1024m
| {{w|Pulsar}}
| A highly magnetized, rotating neutron star that emits a beam of electromagnetic radiation.
|-
| 2.36 ×1024m
| {{w|Great Attractor}}
| An unusual concentration of intergalactic mass.
|-
| 425 ×1021m
| {{w|Antennae Galaxies}} (colliding)
| A pair of colliding galaxies.
|-
| 23.6 ×1021m
| {{w|Andromeda Galaxy}}
| A sibling to our Milky Way. It is the nearest spiral galaxy to ours.
|-
| 9.46 ×1021m
| colspan="2" align="center" style="background: #ffdead;" | One million light years
|-
| 2.38 ×1021m
| [http://knowyourmeme.com/memes/cat-on-a-keyboard-in-space Cat on a keyboard in space]
| An internet meme featuring a picture of a cat sitting on a musical keyboard, superimposed on an image of space.
|-
| 1.56 ×1021m
| {{w|Magellanic Clouds}}
| These clouds are a pair of nearby dwarf galaxies.
|-
| 263 ×1018m
| Edge of Galaxy
| The edge of the {{w|Milky Way}} galaxy, the galaxy in which we reside.
|-
| 245 ×1018m
| {{w|Galactic Center}}
| The center of the Milky Way galaxy.
|-
| 61.5 ×1018m
| {{w|Crab Nebula}}
| Nebula are supernova remnants
|-
| 14.2 ×1018m
| {{w|Horsehead Nebula}}
| A dark nebula that is part of the Orion Constellation.
|-
| 12.7 ×1018m
| {{w|Orion Nebula}}
| A nebula that is part of the Orion Constellation, just south of Orion's Belt.
|-
| 8.14 ×1018m
| {{w|Rigel}}
| The brightest star in the Orion Constellation it is actually a triple star system known alternatively as Beta Orionis
|-
| 6.08 ×1018m
| {{w|Betelgeuse}}
| The star Betelgeuse is displayed along with the location of {{w|Ford_Prefect (character)|Ford Prefect}} on his home planet which orbits Betelgeuse. Ford Prefect is a fictional character from the science fiction parody {{w|The Hitchhiker's Guide to the Galaxy}}.
|-
| 4.20 ×1018m
| {{w|Pleiades}}
| The Pleiades also have a derogatory remark, as per [[66: Abusive Astronomy]]
|-
| 2.90 ×1018m
| The [http://en.memory-alpha.org/wiki/Romulan_Neutral_Zone Romulan Neutral Zone]
| This marks the edge of the {{w|Star Trek}} Federation.
|-
| 931 ×1015m
| colspan="2" align="center" style="background: #ffdead;" | The first radio broadcast was in January 1910. Since radio waves travel at the speed of light, and this was published in September of 2008 this the radio waves traveled about 98.5 light years. See {{w|Contact (1997 film)}} for a depiction of this. This is also referenced in [[1212: Interstellar Memes]].
|-
| 350 ×1015m
| {{w|Arcturus}}
| An orange giant star that is part of the Boötes constellation.
|-
| 320 ×1015m
| {{w|Pollux}}
| One of the most distinct stars in the Gemini Constellation it is large Orange Giant with an apparent visual magnitude of 1.1
|-
| 242 ×1015m
| The edge of {{w|Federation Sector 0-0-1}}
| The sector of space assigned to Earth in {{w|Star Trek}}.
|-
| 224 ×1015m
| {{w|Iraq and weapons of mass destruction|"missing WMDs"}}
| A reference to the alleged weapons of mass destruction that were used as a pretence to mobilize the world population against Iraq, and start the Iraq war.
|-
| 81.3 ×1015m
| {{w|Sirius}}
|Also known as Alpha Canis Majoris, the Dog Star, or the North Star it is actually a binary system of Stars consisting of a main sequence white star and a small white dwarf.
|-
| 56.6 ×1015m
| {{w|Barnard's Star}}
| Barnards star is a very small red giant that is of great interest to astronomers as an achievement in the SIM (Space Interforometry Mission) to find a celestial object out of solar system that is a s small as 3 earth masses
|-
| 41.3 ×1015m
| {{w|Alpha Centauri}}
| Alpha Centauri is the closest star system to our planet.
|-
| 30.9 ×1015m
| colspan="2" align="center" style="background: #ffdead;" | One parsec.
|-
| 9.46 ×1015m
| colspan="2" align="center" style="background: #ffdead;" | One light-year.
|-
| 15.0 ×1015m
| {{w|Oort cloud}}
| A halo of ice balls surrounding our solar system, but missing the {{w|Kupier belt}} between Neptune and the Oort cloud.
|-
| 350 ×1012m
| {{w|Bupkis}}
| Yiddish for "nothing". Only a handful of objects are known to orbit between the Kuiper Belt and the Oort Cloud.
|-
| 55.0 ×1012m
| A comet which will destroy earth in late 2063
| To coincide with the latest biblicaly based prophesy for the [http://www.askelm.com/prophecy/p971105.htm end of the world].
|-
| 19.5 ×1012m
| {{w|Voyager 1}}
| An early space probe. Distance correct as of 20th Nov 2014, click [http://voyager.jpl.nasa.gov/where/ here] to see NASA's live distance counter.
|-
| 16.7 ×1012m
| {{w|Pioneer 10}}
| Listed distance is an estimate based on {{w|Pioneer_10#Current_status|this information}}.
|-
| 17.7 ×1012m
| {{w|Pioneer 11}}
| By the similarity in appearance to Pioneer 10 this unlabeled probe must be Pioneer 11. Listed distance is an estimate based on {{w|Pioneer_11#Current_status|this information}}.
|-
| 14.5 ×1012m
| {{w|Eris (dwarf planet)|Eris}}
| One of a pair of {{w|Trans-Neptunian object}}s now classified as {{w|dwarf planet}}s. The "All hail Discordia!" after Eris is a reference to {{w|Discordianism}}, a somewhat tongue-in-cheek religion based around the goddess Eris. The distance is the maximum distance from earth.
|-
| 7.50 ×1012m
| {{w|Pluto}}
| One of a pair of {{w|Trans-Neptunian object}}s now classified as {{w|dwarf planet}}s. Pluto was originally classified as the 9th planet of the Solar system. Many people was appalled when it was suddenly degraded to dwarf planet. Obviously Randall does not think much of these people thus the comment: ''Not a planet. Neener neener''. The distance is the maximum distance of Pluto from Earth.
|-
| 4.70 ×1012m
| {{w|Neptune}}
| Neptune is displayed here with its moons. Neptune is the eighth and final planet in our solar system.
|-
| 3.20 ×1012m
| {{w|Uranus}}
| Uranus is dispayed here with its moons. Uranus is the seventh planet in our solar system.
|-
| 1.67 ×1012m
| {{w|Saturn}}
| Saturn is displayed along with its moons. One of Saturn's moons, most likely Titan, is labeled as a potential location to find life. Titan is the only known moon to have an atmosphere and oceans. The oceans cannot be filled with liquid water, as it is far too cold, but are instead filled with liquid methane and ethane. Some hypothisize that life could have formed in such oceans.
|-
| 928 ×109m
| {{w|Jupiter}}
| Jupiter is displayed along with its moons. One of Jupiter's moons, most likely Europa, is labeled as a potential location to find life. Europa may be covered by a deep ocean of water found under a layer of ice many kilometers thick. Some hypothisize that life could have formed in such oceans.
|-
| 222 ×109m
| Asteroids
| The {{w|Asteroid|Asteroid belt}} contains a spaceship from {{w|Asteroids (video game)}}
|-
| 133 ×109m
| {{w|Mars}}
| Note the path, reflecting the fact that their distances from Earth vary as the planets move in their orbits with a maximum distance of 261 million km and a minimum of 54.6 million km.
|-
| 114 ×109m
| {{w|Venus}}
| Note the path, reflecting the fact that their distances from Earth vary as the planets move in their orbits with a maximum distance of 401 million km and a minimum of 37.7 million km.
|-
| 138 ×109m
| {{w|Mercury}}
| Mercury is the first planet in out solar system. The distance shown is the maximum distance from Earth.
|-
| 149 ×109m
| {{w|Sun}}
| The Sun is the star at the center of our solar system, around which the Earth orbits.
|-
| 16.3 ×109m
| {{w|Discovery One}}
| The Discovery One from {{w|2001: A Space Odyssey}}, referring to the quote "open the pod bay door, HAL." Also may be a reference to [[375: Pod Bay Doors]].
|-
| 9.43 ×109m
| Planet Express
| The spaceplane is most likely the Planet Express from {{w|Futurama}}, where Fry once discussed "a big heaping bowl of salt."
|-
| 400 ×106m
| Human Altitude Record
| Achieved by the team of {{w|Apollo 13}} approximately 100km higher than the remaining Apollo missions.
|-
| 384 ×106m
| {{w|Moon}}
| The Moon is the Earth's only natural satellite.
|-
| 90.4 ×106m
| {{w|Snoop Dogg}}
| A tongue-in-cheek reference to a rapper notorious for smoking marijuana, shown as having the second-highest altitude record. Someone who is taking drugs is said to be getting high.
|-
| 60.5 ×106m
| {{w|Space elevator}}
| A proposed method of transporting cargo or people into orbit, consisting of a large mass beyond geosynchronous orbit, a station at the geosynchronous point, a cable connecting it to the Earth, and a climber that can scale the cable. Space elevators are also seen in [[697: Tensile vs. Shear Strength]] and [[536: Space Elevators]].
|-
| 42.1 ×106m
| colspan="2" align="center" style="background: #ffdead;" | {{w|Geosynchronous orbit|Geosynchronous Orbit}}
|-
| 20.2 ×106m
| {{w|GPS (satellite)|GPS Satellites}}
| GPS satellites are used for global positioning.
|-
| 3.94 ×106m
| {{w|Lunar Lander}}
| The quote is a reference to {{w|Contact (1997 film)}} where the main character Ellie Arroway after witnessing a celestial light show up close says "Poetry! They should've sent a poet.".
|-
| 800 ×103m
| {{w|Space debris|Space Junk}}
| There is a large quantity of defunct objects in orbit around the earth. Amongst other things, this includes old satellites, rocket stages and fragments from collisions or disintegration. Space junk is also referenced in [[1242: Scary Names]] under the title {{w|Kessler syndrome}}
|-
| 422.5 ×103m
| {{w|International Space Station}}
| The ISS (International Space Station) is a multinational effort to put a research vessel in space. It is currently the largest artifical object in Earth's orbit, as well as the location of the longest continuous human presence in space.
|-
| 100 ×103m
| colspan="2" align="center" style="background: #ffdead;" | The {{w|Edge of space|official edge of space}} as defined by the {{w|Kármán line}}
|-
| 76.0 ×103m
| {{w|Meteors}}
| Meteors are chunks of rock (usually asteroids) that burn up in the atmosphere, producing the bright light associated with them. If the are large enough to hit the ground, they become meterorites, which is why Munroe labeled them only in the upper atmosphere.
|-
| 25.0 ×103m
| {{w|High-altitude balloon|High-altitude balloons}}
| Unmanned balloons, typically filled with helium or hydrogen. The current altitude record was set in 2002 by a balloon named BU60-1 which reached 53,000m.
|-
| 16.1 ×103m
| colspan="2" align="center" style="background: #ffdead;" | 1/10 ATM = 0.1 {{w|Atmospheric pressure|atmosphere of pressure}}
|-
| 12.0 ×103m
| {{w|Airliner|Airliners}}
| This is a typical cruising altitude of jet aircraft, equating to roughly 40,000 feet. (Aircraft altitude tends to be specified in feet rather than metres (yay!) )
|-
| 8.84 ×103m
| {{w|Mount Everest}}
| The Earths highest mountain, located in the {{w|Himalayas|Himalayan mountain range}} in South Asia.
|-
| 8.00 ×103m
| {{w|Cory Doctorow}}
| Cory Doctorow in a balloon, a reference to comic [[239: Blagofaire]].
|-
| 6.34 ×103m
| {{w|Space Shuttle Columbia disaster}}
| The {{w|Space Shuttle Columbia}} and its seven crew were lost when it disintegrated at [http://books.google.co.uk/books?id=6v16AgAAQBAJ&lpg=PA7&ots=LDKQ3nsNHs&dq=shuttle%20columbia%20altitude&pg=PA7#v=onepage&q=shuttle%20columbia%20altitude&f=false approximately 63,400m] in 2003. This number is inconsistent with the height of the graph by a factor of 10 probably a mistype by Randall.
|-
| 6.00 ×103m
| {{w|Helicopter}}
| Though the record for helicopter altitude (without payload) is 12,442m, normal flying is usually performed much lower. In the US, 6000m is into {{w|Class A airspace}}, which is restricted and requires flight under {{w|Instrument Flight Rules}}.
|-
| 6.00 ×103m
| {{w|Cloud}}
| Though not actually labelled there are a couple of clouds shown. While different cloud types vary in height, 6000m is roughly in the middle of the height range for clouds in temperate regions [http://weatherfaqs.org.uk/node/21]
|-
| 5.49 ×103m
| colspan="2" align="center" style="background: #ffdead;" | 1/2 ATM = 0.5 {{w|Atmospheric pressure|atmosphere of pressure}}
|-
| 1.78 ×103m
| [[Cueball]]
| Apparently still using Python as shown in comic [[353: Python]].
|-
| 800 ×100m
| colspan="2" align="center" style="background: #ffdead;" | 800 meters
|-
| 800 ×100m
| {{w|Burj Khalifa|Burj Dubai}}
| Now known as the Burj Khalifa, is the tallest building in the world.
|-
| 500 ×100m
| colspan="2" align="center" style="background: #ffdead;" | 500 meters
|-
| 400 ×100m
| colspan="2" align="center" style="background: #ffdead;" | 400 meters
|-
| 325 ×100m
| {{w|Eiffel Tower}}
| A famous landmark in Paris, France.
|-
| 300 ×100m
| colspan="2" align="center" style="background: #ffdead;" | 300 meters
|-
| 200 ×100m
| colspan="2" align="center" style="background: #ffdead;" | 200 meters
|-
| 150 ×100m
| Kite
| Kite string is commonly sold in large spools; a nice thick spool will probably hold 150 meters.
|-
| 140 ×100m
| {{w|Great Pyramid of Giza}}
| One of the Seven Wonders of the Ancient World. It is located in Egypt.
|-
| 120 ×100m
| {{w|Baseball|Pop Fly}}
| In Baseball a 'Pop Fly' is when the batter mis-hits the baseball, which then follows a tall arc deep into the infield where it's easy picking for the other team to catch on its way down. The highest recorded pop fly, not including those that landed in foul territory, was 172 meters.
|-
| 115 ×100m
| {{w|Redwood Tree|Redwood trees}}
| The tallest trees in the world. At 115.61m (379.3ft) {{w|Hyperion (tree)|Hyperion}}, a Coast Redwood, holds the record for the tallest tree in the world.
|-
| 100 ×100m
| colspan="2" align="center" style="background: #ffdead;" | 100 meters
|-
| 20.0 ×100m
| {{w|Oak}}
| While oaks may grow to be in excess of 40m in height, heights of around 20m are more typical. The person in the tree saying, "Hey, squirrels!" is a reference to [[167: Nihilism]].
|-
| 16.4 ×100m
| Tallest stilts
| The tallest {{w|stilts}} recorded by the Guinness Book of World Records (as of November 2006) were 16.4 meters, or nearly 54 feet.
|-
| 13.0 ×100m
| {{w|Brachiosaurus|Brachiosaur}}
| A large genus of dinosaur.
|-
| 8.00 ×100m
| {{w|Giraffe}}
| The the tallest living terrestrial animal, with fully grown adults reaching in excess of 5m. While labelled 8m in the comic, the [http://www.big-animals.com/the-giraffe-the-worlds-tallest-animal/ record] for height is reported at 5.8m.
|-
| 1.70 ×100m
| {{w|Human height|Folks}}
| Determining an average height of the world population is fraught with complications, but as a ballpark figure 1.7m is fairly accurate.
|}

==Transcript==
:'''Top of observable universe'''
:[Black Hat is standing on top, throwing a black kitty down.]
:Black Cat: Mrowl!
:[Map of the universe from observable universe to Earth. Each area of item is labeled. Labels left to right, up to down:]
:(46 billion light years up)
::Hubble Deep Field Objects
:-One billion light years-
::Great Attractor
::Antennae Galaxies (colliding)
::Andromeda
::Holy crap lots of space
:-One million light years-
::Magellanic Clouds
::Edge of galaxy
::Galactic center
::Crab Nebula
::Orion Nebula
::Horsehead Nebula
::Romulan neutral zone
::The Pleiades, duh!
::Rigel
::Betelgeuse
::Ford Prefect
:[Three arrows are pointing up above three lines with the following label:]
:-Expanding shell of radio transmissions-
::[Above a dotted line:]
::Edge of federation sector 0-0-1
::Pollux
::Arcturus
::Missing WMDs
::Sirius
::Barnard's Star
::Alpha Centauri
:-One parsec-
:-One light year-
::Oort Cloud (?)
::Bupkis
::Comet which will destroy Earth in late 2063
::Pioneer 10
::Voyager I
::Eris (All hail Discordia!)
::Pluto (Not a planet. Neener neener.)
::Neptune
::Uranus
::Saturn
::[Two arrows point to two moons, one next to each of the planets aboe and below.]
::<-- Life -->
::Jupiter
::Asteroids
::Mars
::Venus
::Sun
::Mercury
::Spaceship Planet Express: Hey, a heaping bowl of salt!
::Spaceship Discovery One: Open the fridge door, Hal.
::Moon
::Human altitude record (Apollo 13)
::2nd place: Snoop Dogg
::Space elevator - One of these days, promise!
::Geosynchronous Orbit
::GPS satellites
::Lunar lander: In retrospect, they shouldn't have sent a poet. I have no idea how to land.
::International Space Station
::Space junk
:-Official edge of space (100 km)-
::Meteors
:-1/10 ATM-
::High altitude balloons
::Airliners
::Shuttle Columbia lost
:-1/2 ATM-
::Cory Doctrow
::Everest
::Helicopters (6000 m)
::Cueball: Woo Python!
::[A vertical scale is drawn along the right side of the picture, starting at 1 km and getting progressivly smaller and smaller.]
:1 km
:-800 m-
::Burj Dubai (~800 m)
:500
:400
::Eiffel Tower (325 m)
:200
::Kites
::Great Pyramid (140 m)
::Pop fly
::Redwood (115 m)
:100m
::Oak (20 m)
::A person in the oak: Hey squirrels!
::Tallest stilts
::Brachiosaur (13 m)
::Giraffe (8 m)
::[Megan and Cueball holding the kite are labeled:]
::Folks
:'''The observable universe, from top to bottom''''
::~On a log scale~
::Sizes are not to scale, but heights above the Earth's surface are accurate on a log scale (that is, each step up is double the height.)

{{comic discussion}}
[[Category:Charts]]
[[Category:Large drawings]]
[[Category:Comics with inverted brightness]]
[[Category:Comics featuring Cory Doctorow]]
[[Category:Comics featuring Black Hat]]
[[Category:Comics featuring Cueball]]
[[Category:Comics featuring Megan]]
[[Category:Baseball]]
[[Category:Animals]]
[[Category:Dinosaurs]]
[[Category:Giraffes]]
[[Category:Space]]

User:Erickhagstrom

2015-07-31T13:20:46Z

Erickhagstrom: Created page with "Hi. I'm Erick G. Hagstrom. When I registered I got an error on my email address, but I don't know where to go to fix it. :-("

Hi. I'm Erick G. Hagstrom. When I registered I got an error on my email address, but I don't know where to go to fix it. :-(