explain xkcd - User contributions [en]

1389: Surface Area

2014-07-31T09:43:01Z

141.101.80.212: /* Explanation */ Grammar

{{comic
| number = 1389
| date = July 2, 2014
| title = Surface Area
| image = surface_area.png
| titletext = This isn't an informational illustration; this is a thing I think we should do. First, we'll need a gigantic spool of thread. Next, we'll need some kind of ... hmm, time to head to Seattle.
}}

A [http://xkcd.com/1389/large/ larger version] of this image can be found by clicking the image at xkcd - which can be reached easily from here as always, by clicking on the comic number above.

==Explanation==
This map shows the total {{w|surface area}}s of all {{w|terrestrial planet}}s, {{w|dwarf planet}}s, {{w|natural satellite|moons}}, {{w|asteroid}}s and {{w|minor planet}}s that are larger than 100 m in the {{w|Solar System}}. They have all been represented as regions of a single massive landmass - a {{w|supercontinent}} like {{w|Pangaea}} - which is clearly surrounded by some kind of ocean.

On the area that signifies {{w|Earth}} the {{w|continents}} are drawn using a {{w|map projection}} that keeps the scale of the continents correct. (This is something that [[Randall]] cares about as can be seen in [[977: Map Projections]]). The part of the surface of the Earth that are covered in oceans are also included in the surface area of the Earth (i.e. the map shows the Earths {{w|Crust (geology)|crust}}). An extra layer of 3-4 km of water seems rather insignificant when comparing to the Earth's radius of 6,370 km.

{{w|Moon|The Moon}} has been inlaid in this map next to {{w|Antarctica}} which thus makes a great comparison of how small the Moon is compared to the Earth (there are room for more than 13 lunar surfaces on the Earth). Similarly, it is clear that the planet {{w|Venus}} is almost as big as the Earth.

This is also the general idea of the map - to give an idea about how big the Earth is and how small many of the other known planets etc. are; both compared to earth and to each other. The map drawn on the Earth are probably there mainly as a guide to size, because none of the features that are know on some of the other objects, especially The Moon (i.e. {{w|Impact crater|craters}} and "{{w|Lunar mare|seas}}") and on {{w|Mars}} (i.e. {{w|Olympus Mons}}), are included.

The objects mentioned by name on the map are all but one amongst those that have reached {{w|hydrostatic equilibrium}} and these are all included on this {{w|List of gravitationally rounded objects of the Solar System}}.

The one named object that is '''not''' on the above list is the asteroid {{w|4 Vesta|Vesta}}, which is included because it is the second largest object in the {{w|Asteroid belt}}. It is placed right next to the largest object in this belt, the dwarf planet {{w|Ceres (dwarf planet)|Ceres}}, which is no longer considered an asteroid. And next to these two are the rest of the asteroids in two areas (see below), which thus groups all asteroids together

The only object from the above list, (that qualifies for having a solid surface in hydrostatic equilibrium), '''which is not included''' is the {{w|Saturn}} moon {{w|Mimas (moon)|Mimas}}, which is also clearly the smallest object on the list.

This moon should have been located amongst the other five smaller moons of Saturn between the Earth and {{w|Titan (moon)|Titan}} (the largest of Saturn's moons). Mimas has a surface area of 490,000 km2 which is somewhat smaller than the smallest included Saturn moon {{w|Enceladus}} with a surface area of 799,000 km2.

Generally the moons that belong to a given planet (for those with more than one moon large enough to be included), have been clustered together. Apart from the six (not seven...) moons of Saturn to the right of Earth, the four {{w|Galilean moons}} moons of {{w|Jupiter}} are located above the Earth, the five included moons from {{w|Uranus}} is located to at the top to the far right.

The last planet to have many moons is {{w|Neptune}}, but only {{w|Triton_(moon)|Triton}} is included. This is a fairly large moon, and the only of the 14 known moons of Neptune to be on the above list. However, there is one other moon, {{w|Proteus (moon)|Proteus}} which is notable for being as large as a body of its density can be without being pulled into a spherical shape by its own gravity. It has a length of 424 km in the longest direction, and a mean radius of 210 km. A rough calculation of its surface area from this mean radius gives an area of 550,000 km2, making the surface area slightly larger than Mimas. As there are an '''unlabeled area''' located right next to the other Neptune moon Triton, it is most likely that this small area '''should represent Proteus''', and that it is an error that it was not labeled (or it was a test for followers of xkcd...)

As this is the smallest area, then the cut-off of objects could have been at 500,000 km2, as also Vesta is larger than this, which would make room for Proteus, but explain the missing Mimas.

Two of the included objects also have moons that are large enough to be included: Earth, of course, and the dwarf planet {{w|Pluto}} with its moon {{w|Charon_(moon)|Charon}}. In both cases these moons have been inlaid in the area of their mother planet.

Whereas the moons of the {{w|gas giant}}s and the asteroids have been located above and to the right of the Earth, the planets and dwarf planets have been included below earth (along with the two moons mentioned above). {{w|Mercury (planet)|Mercury}}, Mars and Venus all touching Earth, and then below them the four {{w|Trans-Neptunian object|Trans-Neptunian}} dwarf planets - the {{w|Plutoid}}s.

On the list from above there are, however, also these {{w|List_of_Solar_System_objects_in_hydrostatic_equilibrium#Most_likely_additional_dwarf_planets|10 objects}} which have not been included with name on the map. These object are, however, only likely candidates for being dwarf planets (depending on whether they have reached hydrostatic equilibrium or not), and on the map they have thus been relegated to the sections without individual names. These object are thus probably grouped together (along with other relatively small objects like comets and smaller moons) in the area labeled ''Various small moons, comets, etc'', which is located at the bottom of the map between Mercury and Mars. The surface area for all of these object, when the surface area have been estimated, are larger than 1 million square kilometer, and thus larger than several of the named objects. So it is not the size that is the reason why such objects as {{w|90377 Sedna|Sedna}} and {{w|50000 Quaoar|Quaoar}} are not included with name, but probably the fact they are not investigated enough yet.

The remaining objects in the Solar System with a solid surface are the minor planets, which on the map has been labeled as asteroids even though these objects are grouped together in several other "belts" than the Asteroid belt. Here they have been assigned to two regions at the top of the map. Above the right part of the Earth area is the area ''Asteroids (1 km+)'' which include any object not already included larger than 1 km. (As these objects are no longer round it is the largest dimension, the length, that should be at least 1 km long). And finally the area ''Asteroids (100 m+)'' thus include any object not already included larger than 100 m.

Most of the rest of the objects that have been included in these three sections can likely be found on this {{w|List of Solar System objects by size}}.

Tiny objects smaller than 100 m down to space dust are excluded altogether as explained in the note below the headings. This is probably because their total surface area is impossible to estimate accurately, and also because any estimate would likely be too large to fit easily into the map.

Between Earth and Titan is a tiny speck noted ''all human skin'', which is an interesting sort of solid surface. A rough estimate of the average {{w|body surface area}} and thus of the average area of all {{w|Human skin|humans skin}} can be made from these {{w|Body_surface_area#Average_values|average values}} and from {{w|Population pyramid|population pyramids}} as this [http://populationpyramid.net/world/2015/ pyramid for 2015]. Average adults have a skin area of around 1.7-1.8 m2, but as a large part of the [https://www.census.gov/popclock/ human population] are children (with skin area down to about 0.25 m2 for infants) the total average will be smaller. By extrapolating the given values an average area of about 1.6 m2 can be found. This would make the area 7.2 billion × 1.6 m2 ≈ 11,500 km2. This is 60 times smaller than the smallest of the labeled moons {{w|Miranda (moon)|Miranda}} (of Uranus) with a surface area of 700,000 km2.

The title text jokingly claims that this comic is not actually for information, but rather is something Randall thinks we should really do – that is, to stitch all the solar system's solid surfaces together, as the sub-sub heading says. To do this, we would need a giant spool of thread and then something he has to go get in Seattle… this must be the {{w|Space Needle}}, a needle-like tower in Seattle, which should then be used in this grand project.

Since the land areas are on the surfaces of spheres, this would seem impossible as it would involve lots of deformation and be particularly challenging. It will also be very gruesome when he comes to the part of collecting (and stitching) all human skin together. The inclusion of this speck on the map is, however, also there to make it clear what the real intention is with the planets. Their surface is to be "skinned" of them, as you would have to do with the humans! Then it is all these "planet skins" that should be stitched together using the space needle. This also explains the ragged edges, and why the continents keep their correct size. It would make Randall into a planetary version of {{w|The Silence of the Lambs (film)|The Silence of the Lambs}} movies character ''{{w|Buffalo Bill (character)|Buffalo Bill}}'', a serial killer who tried to make a suit out of the skin from the women he killed.

Randall would also need quite a lot of space for the very large ocean. However, the whole supercontinent is just somewhere between 3-4 times larger than the area of the Earth. And the area of the entire image is less than 9 times the area of the earth. As the {{w|Sphere#Area|formula}} for calculation surface areas for {{w|sphere}}s (4*π*r2) goes with the radius (r) squared, the diameter of the planet needed for the experiment do not need to be larger than 3 times that of the earth. Although there are no objects in the Solar System with this particular size, it is still much much smaller than the {{w|gas giant}}s, the smallest of these have a radius of almost 4000 times that of the earth! {{w|Exoplanet}}s with this range of diameters have certainly been found, however, already at {{w|Exoplanet#Super-Earths.2C_mini-Neptunes.2C_and_gas_dwarfs|1.7 times the earth radius}} most planets size to be of the {{w|Super-Earth}} type and turns in to the {{w|Gas_dwarf#Gas_dwarf|gas dwarf}} type of planets. So an ocean of the size needed are not easy to come by...

As has been explained above the earth's surface is included disregarding surface water (oceans) and the same is valid for other objects with surface water, as the Saturn moon Titan which has great lakes (or even oceans) of liquid {{w|methane}} on the surface or the Jupiter moon {{w|Europa (moon)|Europa}} which is covered in a deep ocean with a thick cap of ice. (Interestingly this moon is placed on the map very near to the continent of {{w|Europe}} - maybe for easy comparison of these two areas).

The gas giants Jupiter, Saturn, Uranus, and Neptune has, however, not been included because they do not have any "solid surfaces"; even if they had a solid core (which is itself not clear), this would not comprise any "surface". The gas giants are believed to lack any well-defined surface at all, with the gases that make them up simply becoming thinner and thinner with increasing distance from the planets' centers, eventually becoming indistinguishable from the interplanetary medium. But if they were included via some sort of surface definition, the map of this comic would become a tiny speck amongst the map of the gas giants. Similarly, the surface of the {{w|Sun}} is also not considered a solid surface but hot {{w|Plasma_(physics)|plasma}}; if it was included it would reduce even a map of the gas giants to a tiny speck.

The map is drawn in a similar style to the two maps of the Internet that Randall has created in the past:
*[[256: Online Communities]]
*[[802: Online Communities 2]]

===Data table===
Below is a table listing the object roughly in the order they would be read of the map (the same order as in the transcript.) But they can be sorted by each of the columns.

The data is taken when possible from the following table: {{w|List of gravitationally rounded objects of the Solar System}}, and surface area is given with three significant digits.

For {{w|4 Vesta|Vesta}} and {{w|Proteus (moon)|Proteus}} (the most likely candidate for the unlabeled area next to triton) the area is calculated from their mean radius (i.e. they are not spherical). See also above in the explanation, also for calculating the area of all human skin...

The surface for a given object is also given as a ''Fraction of Earth’s surface'', and from this the number of times the object could be placed on the Earth's surface is given as one divided by this fraction. For instance it can be seen that The Moon's surface can be placed more than 13 times on top of that of the Earth.

{| class="wikitable sortable"
|+Surface area of mentioned objects
!Object
!Type
!Surface area (km2)
!Fraction of Earth’s
!1/Fraction
|-
|{{w|Io (moon)|Io}}||Moon of Jupiter||data-sort-value="41900000"| 4.19×107||0.082||12.2
|-
|{{w|Callisto (moon)|Callisto}}||Moon of Jupiter||data-sort-value="73000000"| 7.30×107||0.143||7.00
|-
|{{w|Europa (moon)|Europa}}||Moon of Jupiter||data-sort-value="30900000"| 3.09×107||0.061||16.4
|-
|{{w|Ganymede (moon)|Ganymede}}||Moon of Jupiter||data-sort-value="87000000"| 8.70×107||0.171||5.80
|-
|{{w|Ceres (dwarf planet)|Ceres}}||Dwarf planet||data-sort-value="2800000"| 2.80×106||0.0055||180
|-
|{{w|4 Vesta|Vesta}}||Asteroid||data-sort-value="870000"| 8.70×105||0.0017||590
|-
|{{w|Asteroids}} (1 km+)||Asteroid||N/A||N/A||N/A
|-
|{{w|Proteus (moon)|Proteus}} (not labeled)||Moon of Neptune||data-sort-value="550000"| 5.50×105||0.00011||910
|-
|{{w|Triton (moon)|Triton}}||Moon of Neptune||data-sort-value="23000000"| 2.30×107||0.045||22.2
|-
|{{w|Asteroids}} (100 m+)||Asteroid||N/A||N/A||N/A
|-
|{{w|Oberon (moon)|Oberon}}||Moon of Uranus||data-sort-value="7290000"| 7.29×106||0.014||71.4
|-
|{{w|Miranda (moon)|Miranda}}||Moon of Uranus||data-sort-value="700000"| 7.00×105||0.0014||714
|-
|{{w|Ariel (moon)|Ariel}}||Moon of Uranus||data-sort-value="4210000"| 4.21×106||0.008||125
|-
|{{w|Umbriel (moon)|Umbriel}}||Moon of Uranus||data-sort-value="4300000"| 4.30×106||0.008||125
|-
|{{w|Titania (moon)|Titania}}||Moon of Uranus||data-sort-value="7820000"| 7.82×106||0.015||66.7
|-
|{{w|Earth}}||Planet||data-sort-value="510000000"| 5.10×108||1||1
|-
|{{w|Tethys (moon)|Tethys}}||Moon of Saturn||data-sort-value="4940000"| 3.574×106||0.007||143
|-
|{{w|Enceladus}}||Moon of Saturn||data-sort-value="799000"| 7.99×105||0.0016||625
|-
|{{w|Dione (moon)|Dione}}||Moon of Saturn||data-sort-value="3970000"| 3.97×106||0.0078||128
|-
|{{w|Iapetus (moon)|Iapetus}}||Moon of Saturn||data-sort-value="6700000"| 6.70×106||0.0132||75.8
|-
|All {{w|Human skin|humans skin}}||Human organ||data-sort-value="11500"| 1.15×104||0.000023||43400
|-
|{{w|Rhea (moon)|Rhea}}||Moon of Saturn||data-sort-value="7340000"| 7.34×106||0.0144||69.4
|-
|{{w|Titan (moon)|Titan}}||Moon of Saturn||data-sort-value="83000000"| 8.30×107||0.163||6.14
|-
|{{w|Mercury (planet)|Mercury}}||Planet||data-sort-value="75000000"| 7.50×107||0.147||6.80
|-
|{{w|Moon|The Moon}}||Moon of Earth||data-sort-value="37900000"| 3.79×107||0.074||13.5
|-
|Various small {{w|Natural satellite|moons}}, {{w|comet}}s, etc.||N/A||N/A||N/A||N/A
|-
|{{w|Mars}}||Planet||data-sort-value="140000000"| 1.40×108||0.2745||3.64
|-
|{{w|Makemake (dwarf planet)|Makemake}}||Dwarf planet||data-sort-value="6400000"| 6.40×106||0.013||76.8
|-
|{{w|Haumea (dwarf planet)|Haumea}}||Dwarf planet||data-sort-value="6800000"| 6.80×106||0.0133||75.2
|-
|{{w|Eris (dwarf planet)|Eris}}||Dwarf planet||data-sort-value="18000000"| 1.80×107||0.0353||28.3
|-
|{{w|Pluto}}||Dwarf planet||data-sort-value="17000000"| 1.70×107||0.0333||30.0
|-
|{{w|Charon (moon)|Charon}}||Moon of Pluto||data-sort-value="4580000"| 4.58×106||0.009||111
|-
|{{w|Venus}}||Planet||data-sort-value="460000000"| 4.60×108||0.901||1.10
|}

==Transcript==
:[At the top of a map is a heading, with two sub headings and a note in brackets:]
:'''Space'''
:Without the space
:The Solar System’s solid surfaces stitched together
:(Excluding dust and small rocks)
:[Below the headings there is a map with several distinct areas. Each area is labelled with a name or a description. This label is noted inside the area, except for areas that are too small; here the label is written outside and a line indicates which area the label belongs to. Only exception is the largest area, on which the contours of the Earth’s continents are drawn. Surrounding the map is wavy lines to indicate that this is either an island or one big super-continent placed in an even larger ocean.]
:[Here below are the labels given as they appear in “normal” reading order in as read from left to right in the three main rows as will be indicated:]
:[Row one, above the line defined by the general top of the Earth area:]
:Io
:Callisto
:Europa
:Ganymede
:Ceres
:Vesta
:Asteroids (1 km+)
:[Here – above the Asteroids area before the Triton area - is a small unlabelled area (the only other except Earth)]
:Triton
:Asteroids (100 m+)
:Oberon
:Miranda
:Ariel
:Umbriel
:Titania
:[Row two, the unlabelled Earth area's row, but here only given those that are directly written to the right of this area:]
:Tethys
:Enceladus
:Dione
:Iapetus
:All human skin
:Rhea
:Titan
:[Row three, all the remaining items that are mainly below the Earth area:]
:Mercury
:The Moon
:Various small moons, comets, etc
:Mars
:Makemake
:Haumea
:Eris
:Pluto
:Charon
:Venus

{{comic discussion}}

[[Category:Comics with color]]
[[Category:Large drawings]]
[[Category:Maps]]
[[Category:Space]]
[[Category:Astronomy]]

Talk:493: Actuarial

2014-07-14T11:18:56Z

141.101.80.212: Could his choice of year be related to the end of Unix time?

I have no time for searching right now, but I'm sure there is a graph comic related to this sentence: "2038: Last of the original Star Wars cast dies." BTW: please create only pages with an proper explanation. --[[User:Dgbrt|Dgbrt]] ([[User talk:Dgbrt|talk]]) 16:45, 6 June 2013 (UTC)

While I'm not the guy/gal who created the page, I thought I'd supply a short explanation, to be refined as necessary. BTW, the linkies at the bottom suggest that this is a "Comic with colour", but I only see monochrome. Is this a human error, or is it an automated response to the supplied image (while being black on white, or maybe greyscale) 'officially' having a colour palette or something in its header? [[Special:Contributions/178.107.63.150|178.107.63.150]] 23:35, 6 June 2013 (UTC)

His choice of year 2038 could be related to the year 2038 problem. If we assume that C3PO and R2D2 run Unix, then the year 2038 would be the end of Unix time, and they would therefore die. [[Special:Contributions/141.101.80.212|141.101.80.212]] 11:18, 14 July 2014 (UTC)

710: Collatz Conjecture

2014-07-13T23:17:47Z

141.101.80.212: /* Explanation */

{{comic
| number = 710
| date = March 5, 2010
| title = Collatz Conjecture
| image = collatz_conjecture.png
| titletext = The Strong Collatz Conjecture states that this holds for any set of obsessively-hand-applied rules.
}}

==Explanation==
The {{w|Collatz conjecture}} is a longstanding unsolved problem in mathematics. It states that repeating the sequence of operations described in the comic will eventually lead to the number 1. The description in the comic starts out accurate, then veers into the joke.

The comic illustrates the sequence with a graph in which an arrow connects each number to its successor. For example, the number 22 is even, so the next number in the sequence is 22 ÷ 2 = 11, and there is an arrow from 22 to 11. On the other hand 11 is odd, so the next number is 3 × 11 + 1 = 34, and there is an arrow from 11 to 34.

According to the title text, [[Cueball]] is obsessively writing out the graph by hand, and is so preoccupied with the task that he has stopped socializing with his friends. He will be busy for a very long time, because the Collatz conjecture has been confirmed for all starting values up to 5 × 1018.

The ''Strong Collatz Conjecture'' in the title text is a humorous extension of the Collatz Conjecture. Some other mathematical conjectures and axioms also have normal and Strong variants, where the Strong variant gives a more general rule. This practice is further parodied in [[1310: Goldbach Conjectures]].

==Transcript==
:[Cueball sits in a chair at a desk, papers piled on top, writing furiously. Depicted above are apparently the writing, a series of nodes in various Collatz sequences (starting with 7, 21, 24, 29, 106, 176 and 256), all eventually leading back to 1.]
:The Collatz Conjecture states that if you pick an number, and if it's even divide it by two and if it's odd multiply it by three and add one, and you repeat this procedure long enough, eventually your friends will stop calling to see if you want to hang out.

{{comic discussion}}
[[Category:Comics featuring Cueball]]
[[Category:Math]]

1362: Morse Code

2014-05-07T09:34:42Z

141.101.80.212: /* Explanation */ +

{{comic
| number = 1362
| date = April 30, 2014
| title = Morse Code
| image = morse_code.png
| titletext = Oh, because Facebook has worked out SO WELL for everyone.
}}

==Explanation==
[[Cueball]] recounts the last message sent by the French Navy upon retiring {{W|morse code}}.

The poetic, and potentially angsty-sounding nature of the message reminds him of the on-line journal website {{W|LiveJournal}}, which was popular until the late 00s (it was launched in 1999), and stereotypically used by angst-ridden teenagers to post song lyrics, poems, or cryptic messages to express their emotions and possibly fish for attention. Since Cueball never uses his LiveJournal account any more, he wonders if he can find the password again. He might be considering posting the final Morse Code message as his own last and final message on his LiveJournal.

The popularity of the site died down considerably with the arrival of social networking sites like {{W|MySpace}}, {{W|Facebook}}, {{W|Google Plus}} and the advent of microblogging platforms like {{W|Twitter}} and {{W|Tumblr}}. LiveJournal has also lost a lot of users since a Russian company bought them out; Russian dissidents used LiveJournal to present their opinions, and the Russian government used to retaliate by creating "denial of service" attacks which make LiveJournal unusable for all its users, sometimes for days. Nowadays (May 2014) LiveJournal is still quite popular among Russian-speaking people, including dissenters, but its administration was forced to show {{w|HTTP 451}} error in some cases (e. g., when a user with a Russian IP is trying to read {{w|Alexei Navalny}} blog) with new laws. Thus when [[Megan]] is upset with his desire to let LiveJournal die out like the Morse Code, Cueball describes it as "a nice place to go for some peace and quiet".

The title text is Megan's (or [[Randall|Randall's]]) sarcastic remark indicating that Facebook is no less filled with angst-ridden thoughts than LiveJournal was, nor is it free from problems or controversies around other issues such as security or privacy.

==Transcript==
:[Cueball and Megan are lying in a grassy, lonely plain.]

:Cueball: When the French navy retired morse code in 1997, they broadcast a final message: "Calling all. This is our last cry before our eternal silence."

:Cueball: I wonder if I can find my Livejournal login.
:Megan: Hey, I ''like'' Livejournal.
:Cueball: It's a nice place to go for some peace and quiet, I suppose.

==Trivia==
The Morse code for the final message "Calling all. This is our last cry before our eternal silence." is:
-.-. .- .-.. .-.. .. -. --. .- .-.. .-.. .-.-.- - .... .. ... .. ... --- ..- .-. .-.. .- ... - -.-. .-. -.-- -... . ..-. --- .-. . --- ..- .-. . - . .-. -. .- .-.. ... .. .-.. . -. -.-. . .-.-.-
A period is a very short tone while the hyphen represents a slightly longer one. Between each character there is a small pause. This message was typically sent within less than half a minute.

==External links==
* [http://www.highbeam.com/doc/1G1-53668116.html An obituary for Morse code]
* [https://fr.wikipedia.org/wiki/500_kHz_%28maritime_et_a%C3%A9ronautique%29?uselang=en#Nuit_du_31.C2.A0janvier.C2.A01997_au_1er.C2.A0f.C3.A9vrier.C2.A01997.2C Transcript of communications of the french station that night]
* [http://www.onlineconversion.com/morse_code.htm Convert text to morse code and vice versa]

{{comic discussion}}
[[Category:Comics featuring Cueball]]
[[Category:Comics featuring Megan]]
[[Category:Social networking]]