explain xkcd - User contributions [en]

1145: Sky Color

2012-12-10T16:27:35Z

174.125.142.147: /* Explanation */

{{comic
| number = 1145
| date = December 10, 2012
| title = Sky Color
| image = sky color.png
| titletext = Feynman recounted another good one upperclassmen would use on freshmen physics students: When you look at words in a mirror, how come they're reversed left to right but not top to bottom? What's special about the horizontal axis?
}}

==Explanation==
The point of this comic is that often, curious children ask their parents simple questions about understanding how the world works. [[Randall]]'s hobby is to make those questions infinitely harder to stump the parents and make them uncomfortable.

{{W|Rayleigh scattering}} is the phenomenon that explains the color of the sky, where light of every wavelength gets scattered in the air by the fourth root of its wavelength as given in the comic. In the {{w|visible spectrum}}, blue light has a wavelength of 450–495 nm while violet has a shorter wavelength of 380–450 nm. Violet light does indeed get scattered more than blue light, however the lower portion of the spectrum for sunlight consists of blue light and eyes are much more sensitive to blue light than violet light. This leaves the impression of a blue sky. Good explanation, including why blue and not violet, can be found in [http://math.ucr.edu/home/baez/physics/General/BlueSky/blue_sky.html Usenet Physics FAQ :: Why is the sky blue?] (but note that human color perception [http://blog.asmartbear.com/color-wheels.html is more complicated] than described there).

The title text refers to a {{w|mirror image}}, and is discussed by Richard Feynman in a famous BBC documentary (http://www.youtube.com/watch?v=6tuxLY94LXw), as one of the problems which he used have fun with with first years.

A mirror image is a virtual image produced by the reflection of light on a mirror. In the mirror image, only front and back are switched around. Left and right are still left and right in an absolute reference frame. The start of the word would still be closest to the door, the end of the word closest to the window, as in the real room, only the person in the mirror is facing the other way. The apparent inversion comes from the fact that the mind projects itself onto the person in the mirror, and the writing on his paper will be illegible (from "his" right to left instead of from "his" left to right)

To help understand why this effect happens, imagine that you are holding a sign which says "MIX" and facing a mirror. Initially, you face the sign towards you. The M is on the left and the X on the right. Now, you turn the sign around so that the sign faces the mirror. Now, even without paying any attention to the mirror, simply because you have turned it around, now the M is on the right and the X is on the left and if you could see through the back of the sign, it would say "XIM" from your perspective. When you look at it in the mirror, you are now able to see that orientation and it appears to read "XIM". If instead of turning the sign around horizontally to look at it in the mirror, you flipped it vertically and looked at it in the mirror, it would appear to say "WIX" in the mirror. Thus the mirror is only revealing how the text is oriented relative to your eyes. (Or, to put it more succinctly: mirrors ''don't'' reverse left to right, ''turning around'' does.)

{{W|Richard Feynman}} was a famous American theoretical physicist.

==Transcript==
:[Girl and her mother, Megan. Megan is at a desk and facing the girl.]
:Girl: Mommy, why is the sky blue?
:Megan: Rayleigh scattering! Short wavelengths get scattered ''way'' more (proportional to 1/''λ''4). Blue light dominates because it's so short.
:Girl: Oh.
:Girl: So why ''isn't'' the sky violet?
:Megan: Well, because, uh... ...hmm.

:Caption: My hobby: Teaching tricky questions to the children of my scientist friends.

{{comic discussion}}
[[Category:Comics featuring Megan]]
[[Category:Physics]]
[[Category:My Hobby]]

1145: Sky Color

2012-12-10T16:26:30Z

174.125.142.147: /* Explanation */

{{comic
| number = 1145
| date = December 10, 2012
| title = Sky Color
| image = sky color.png
| titletext = Feynman recounted another good one upperclassmen would use on freshmen physics students: When you look at words in a mirror, how come they're reversed left to right but not top to bottom? What's special about the horizontal axis?
}}

==Explanation==
The point of this comic is that often, curious children ask their parents simple questions about understanding how the world works. [[Randall]]'s hobby is to make those questions infinitely harder to stump the parents and make them uncomfortable.

{{W|Rayleigh scattering}} is the phenomenon that explains the color of the sky, where light of all wavelengths gets scattered in the air by the fourth root of its wavelength as given in the comic. In the {{w|visible spectrum}}, blue light has a wavelength of 450–495 nm while violet has a shorter wavelength of 380–450 nm. Violet light does indeed get scattered more than blue light, however the lower portion of the spectrum for sunlight consists of blue light and eyes are much more sensitive to blue light than violet light. This leaves the impression of a blue sky. Good explanation, including why blue and not violet, can be found in [http://math.ucr.edu/home/baez/physics/General/BlueSky/blue_sky.html Usenet Physics FAQ :: Why is the sky blue?] (but note that human color perception [http://blog.asmartbear.com/color-wheels.html is more complicated] than described there).

The title text refers to a {{w|mirror image}}, and is discussed by Richard Feynman in a famous BBC documentary (http://www.youtube.com/watch?v=6tuxLY94LXw), as one of the problems which he used have fun with with first years.

A mirror image is a virtual image produced by the reflection of light on a mirror. In the mirror image, only front and back are switched around. Left and right are still left and right in an absolute reference frame. The start of the word would still be closest to the door, the end of the word closest to the window, as in the real room, only the person in the mirror is facing the other way. The apparent inversion comes from the fact that the mind projects itself onto the person in the mirror, and the writing on his paper will be illegible (from "his" right to left instead of from "his" left to right)

To help understand why this effect happens, imagine that you are holding a sign which says "MIX" and facing a mirror. Initially, you face the sign towards you. The M is on the left and the X on the right. Now, you turn the sign around so that the sign faces the mirror. Now, even without paying any attention to the mirror, simply because you have turned it around, now the M is on the right and the X is on the left and if you could see through the back of the sign, it would say "XIM" from your perspective. When you look at it in the mirror, you are now able to see that orientation and it appears to read "XIM". If instead of turning the sign around horizontally to look at it in the mirror, you flipped it vertically and looked at it in the mirror, it would appear to say "WIX" in the mirror. Thus the mirror is only revealing how the text is oriented relative to your eyes. (Or, to put it more succinctly: mirrors ''don't'' reverse left to right, ''turning around'' does.)

{{W|Richard Feynman}} was a famous American theoretical physicist.

==Transcript==
:[Girl and her mother, Megan. Megan is at a desk and facing the girl.]
:Girl: Mommy, why is the sky blue?
:Megan: Rayleigh scattering! Short wavelengths get scattered ''way'' more (proportional to 1/''λ''4). Blue light dominates because it's so short.
:Girl: Oh.
:Girl: So why ''isn't'' the sky violet?
:Megan: Well, because, uh... ...hmm.

:Caption: My hobby: Teaching tricky questions to the children of my scientist friends.

{{comic discussion}}
[[Category:Comics featuring Megan]]
[[Category:Physics]]
[[Category:My Hobby]]

1145: Sky Color

2012-12-10T16:25:42Z

174.125.142.147: /* Explanation */

{{comic
| number = 1145
| date = December 10, 2012
| title = Sky Color
| image = sky color.png
| titletext = Feynman recounted another good one upperclassmen would use on freshmen physics students: When you look at words in a mirror, how come they're reversed left to right but not top to bottom? What's special about the horizontal axis?
}}

==Explanation==
The point of this comic is that often, curious children ask their parents simple questions about understanding how the world works. [[Randall]]'s hobby is to make those questions infinitely harder to stump the parents and make them uncomfortable.

{{W|Rayleigh scattering}} is the phenomenon that explains the color of the sky, where light of all wavelengths gets scattered in the air by the fourth root of the wavelength as given in the comic. In the {{w|visible spectrum}}, blue light has a wavelength of 450–495 nm while violet has a shorter wavelength of 380–450 nm. Violet light does indeed get scattered more than blue light, however the lower portion of the spectrum for sunlight consists of blue light and eyes are much more sensitive to blue light than violet light. This leaves the impression of a blue sky. Good explanation, including why blue and not violet, can be found in [http://math.ucr.edu/home/baez/physics/General/BlueSky/blue_sky.html Usenet Physics FAQ :: Why is the sky blue?] (but note that human color perception [http://blog.asmartbear.com/color-wheels.html is more complicated] than described there).

The title text refers to a {{w|mirror image}}, and is discussed by Richard Feynman in a famous BBC documentary (http://www.youtube.com/watch?v=6tuxLY94LXw), as one of the problems which he used have fun with with first years.

A mirror image is a virtual image produced by the reflection of light on a mirror. In the mirror image, only front and back are switched around. Left and right are still left and right in an absolute reference frame. The start of the word would still be closest to the door, the end of the word closest to the window, as in the real room, only the person in the mirror is facing the other way. The apparent inversion comes from the fact that the mind projects itself onto the person in the mirror, and the writing on his paper will be illegible (from "his" right to left instead of from "his" left to right)

To help understand why this effect happens, imagine that you are holding a sign which says "MIX" and facing a mirror. Initially, you face the sign towards you. The M is on the left and the X on the right. Now, you turn the sign around so that the sign faces the mirror. Now, even without paying any attention to the mirror, simply because you have turned it around, now the M is on the right and the X is on the left and if you could see through the back of the sign, it would say "XIM" from your perspective. When you look at it in the mirror, you are now able to see that orientation and it appears to read "XIM". If instead of turning the sign around horizontally to look at it in the mirror, you flipped it vertically and looked at it in the mirror, it would appear to say "WIX" in the mirror. Thus the mirror is only revealing how the text is oriented relative to your eyes. (Or, to put it more succinctly: mirrors ''don't'' reverse left to right, ''turning around'' does.)

{{W|Richard Feynman}} was a famous American theoretical physicist.

==Transcript==
:[Girl and her mother, Megan. Megan is at a desk and facing the girl.]
:Girl: Mommy, why is the sky blue?
:Megan: Rayleigh scattering! Short wavelengths get scattered ''way'' more (proportional to 1/''λ''4). Blue light dominates because it's so short.
:Girl: Oh.
:Girl: So why ''isn't'' the sky violet?
:Megan: Well, because, uh... ...hmm.

:Caption: My hobby: Teaching tricky questions to the children of my scientist friends.

{{comic discussion}}
[[Category:Comics featuring Megan]]
[[Category:Physics]]
[[Category:My Hobby]]

1145: Sky Color

2012-12-10T16:20:47Z

174.125.142.147: /* Explanation */

{{comic
| number = 1145
| date = December 10, 2012
| title = Sky Color
| image = sky color.png
| titletext = Feynman recounted another good one upperclassmen would use on freshmen physics students: When you look at words in a mirror, how come they're reversed left to right but not top to bottom? What's special about the horizontal axis?
}}

==Explanation==
The point of this comic is that often, curious children ask their parents simple questions about understanding how the world works. [[Randall]]'s hobby is to make those questions infinitely harder to stump the parents and make them uncomfortable.

{{W|Rayleigh scattering}} is the phenomenon that explains the color of the sky, where light of shorter wavelengths gets scattered in the air by the fourth root of the wavelength as given in the comic. In the {{w|visible spectrum}}, blue light has a wavelength of 450–495 nm while violet has a shorter wavelength of 380–450 nm. Violet light does indeed get scattered more than blue light, however the lower portion of the spectrum for sunlight consists of blue light and eyes are much more sensitive to blue light than violet light. This leaves the impression of a blue sky. Good explanation, including why blue and not violet, can be found in [http://math.ucr.edu/home/baez/physics/General/BlueSky/blue_sky.html Usenet Physics FAQ :: Why is the sky blue?] (but note that human color perception [http://blog.asmartbear.com/color-wheels.html is more complicated] than described there).

The title text refers to a {{w|mirror image}}, and is discussed by Richard Feynman in a famous BBC documentary (http://www.youtube.com/watch?v=6tuxLY94LXw), as one of the problems which he used have fun with with first years.

A mirror image is a virtual image produced by the reflection of light on a mirror. In the mirror image, only front and back are switched around. Left and right are still left and right in an absolute reference frame. The start of the word would still be closest to the door, the end of the word closest to the window, as in the real room, only the person in the mirror is facing the other way. The apparent inversion comes from the fact that the mind projects itself onto the person in the mirror, and the writing on his paper will be illegible (from "his" right to left instead of from "his" left to right)

To help understand why this effect happens, imagine that you are holding a sign which says "MIX" and facing a mirror. Initially, you face the sign towards you. The M is on the left and the X on the right. Now, you turn the sign around so that the sign faces the mirror. Now, even without paying any attention to the mirror, simply because you have turned it around, now the M is on the right and the X is on the left and if you could see through the back of the sign, it would say "XIM" from your perspective. When you look at it in the mirror, you are now able to see that orientation and it appears to read "XIM". If instead of turning the sign around horizontally to look at it in the mirror, you flipped it vertically and looked at it in the mirror, it would appear to say "WIX" in the mirror. Thus the mirror is only revealing how the text is oriented relative to your eyes. (Or, to put it more succinctly: mirrors ''don't'' reverse left to right, ''turning around'' does.)

{{W|Richard Feynman}} was a famous American theoretical physicist.

==Transcript==
:[Girl and her mother, Megan. Megan is at a desk and facing the girl.]
:Girl: Mommy, why is the sky blue?
:Megan: Rayleigh scattering! Short wavelengths get scattered ''way'' more (proportional to 1/''λ''4). Blue light dominates because it's so short.
:Girl: Oh.
:Girl: So why ''isn't'' the sky violet?
:Megan: Well, because, uh... ...hmm.

:Caption: My hobby: Teaching tricky questions to the children of my scientist friends.

{{comic discussion}}
[[Category:Comics featuring Megan]]
[[Category:Physics]]
[[Category:My Hobby]]

Talk:1143: Location

2012-12-05T15:25:39Z

174.125.142.147:

I thought the words "like" and "hang out" were references to facebook's "like" and google's "hang out". What do the native speakers think? {{unsigned|213.252.171.254|07:56, 5 December 2012 (UTC)}}

: Not in this case- here they're just being used as the everyday terms that facebook and google co-opted. {{unsigned|140.247.0.10|08:12, 5 December 2012 (UTC)}}

:: I agree. {{unsigned|122.60.40.91|09:28, 5 December 2012 (UTC)}}

: Native speaker here: there doesn't seem to be anything distinctive about the use of 'like' and 'hang out' in this comic to indicate they might be references. {{unsigned|170.194.32.42|10:33, 5 December 2012 (UTC)}}

:: The words aren't out of place otherwise, so it just might be a (big) coincidence. I still find it likely to be true. [[Special:Contributions/207.237.164.241|207.237.164.241]] 11:18, 5 December 2012 (UTC)

: Another native speaker here. You typically would not "hang out" – in real life – with people you don't "like" – as in you like your friends. There's nothing in the comic to make me think there's any connection with Facebook or Google+. [[Special:Contributions/24.41.5.167|24.41.5.167]] 11:44, 5 December 2012 (UTC)

This native speaker agrees. The dialog is ordinary informal American English. That's why facebook and Google hijacked the words. Facebook and Google want to be seen as informal and idiomatic institutions.

1141: Two Years

2012-11-30T16:31:20Z

174.125.142.147: /* Explanation */

{{comic
| number = 1141
| date = November 30, 2012
| title = Two Years
| image = two years.png
| imagesize =
| titletext = She won the first half of all our chemo Scrabble games, but then her IV drugs started kicking in and I *dominated*.
}}

== Explanation ==

This comic marks the second year of [[Randall Munroe]]'s wife's battle with cancer, and appears to depict actual events from those two years. Randall's wife's cancer has been the subject of [[:Category:Cancer|several previous comics]].

Some explanations:
* Panel 1: Randall's wife (at that point, his girlfriend or fiancée) receives a diagnosis over the phone as Randall sits by her side supportively
* Panel 2: Depicts Randall's wife undergoing {{w|chemotherapy}} through an IV. Because of the hair loss that results from chemotherapy, many patients opt to shave their heads when they undergo chemotherapy. Her hair grows back over the course of the following panels.
* Panel 4: Randall and his wife are waiting for the results of a scan; it appears a phone is on the middle of the table that they are waiting to ring.
* Panel 5: More chemotherapy. Randall and his wife are playing {{w|Scrabble}}, as referenced in the title text, which is a very popular board game in which players use letter tiles to spell words in a cross-word style. Randall's wife uses the fact that she has cancer as leverage to get Randall to ignore the fact that the word she has played (zarg) is not a real word.
* Panel 6: Someone suggests Randall and his wife come for a visit next year, but all they can think about are the words "next year", suggesting their fears that Randall's wife won't be able to go anywhere, or might even be dead by next year.
* Panel 7: Randall and his wife get married.
* Panel 9: Randall is paraphrasing a line from the song "{{w|Still Alive}}" ([http://www.youtube.com/watch?v=l_S0PGu-cH4 video]) from the video game ''{{w|Portal}}'' (''"I'm doing science and I'm still alive"'').
* Panel 10: Randall and his wife have dinner to celebrate the fact that she has made it two years since her biopsy.

==Transcript==
:[Randall and his wife sitting on a bed and on the phone with a nurse.]
:Randall's wife: oh god

:[Randall and his wife sitting at their laptops. Randall's wife is hooked up to a dialysis machine and her hair is shaved.]
:Machine: ...BEEEP...BEEEP...BEEEP...

:[Randall and his wife rowing. His wife is wearing a beanie.]

:[Randall and his wife sitting at a table. A clock is mounted behind them.]
:Randall's wife: How long can it take to read a scan!?

:[Randall and his wife playing scrabble.]
:Randall: "Zarg" isn't a word.
:Randall's wife: But ''Caaancer''.
:Randall: ...Ok, fine.

:[Randall and his wife talking to a friend. A large thought bubble is above their heads.]
:Friend: So next year you should come visit us up in the mountain - [cut off by thought bubble]
:Randall and wife: "Next year"

:[Randall and his wife getting married. A heart is above their heads. His wife's hair is growing back.]

:[Randall and his wife watching a whale jump out of the water.]

:[Randall watching his wife use a laptop.]
:Randall: Hey-
:Randall: You're doing science,
:Randall: And you're still alive.
:Randall's wife: Yeah!

:[Randall and his wife under a tree.]
:Randall: It's only been two years?
:Randall's wife: They were big years.

:[Randall and his wife at a fancy restaurant being served.]
:Waiter: Happy... Anniversary?
:Randall's wife: Biopsy-versary!
:Waiter: ...eww.

{{comic discussion}}
[[Category:Comics featuring Randall Munroe]]
[[Category:Cancer]]

Talk:1138: Heatmap

2012-11-24T00:28:29Z

174.125.142.147:

So does this mean... that all the subscribers to Martha Stweart Living are secretly furries? *gasp* [[Special:Contributions/129.97.124.23|129.97.124.23]] 23:00, 23 November 2012 (UTC)

Clearly it means that the furries are, in general, Martha Stewart fans, not the reverse. Are you mad?