explain xkcd - User contributions [en]

Talk:3023: The Maritime Approximation

2024-12-12T04:28:47Z

172.68.54.64:

1.609*3.1416926 looks like 1.852*2.718281828
''seems legit'' {{unsigned ip|172.71.124.233|21:37, 11 December 2024 (UTC)}}

I added the basics of an explanation, it definitely needs some work, but it should do as a starting point. Hope I did well! [[Special:Contributions/172.68.22.92|172.68.22.92]] 23:06, 11 December 2024 (UTC)

The knot is exactly 1 nautical mile per hour. Meanwhile π/e ≈ 1.155727, which is close to nm/mi = kt/mph ≈ 1.15078
[[Special:Contributions/172.70.134.135|172.70.134.135]] 23:26, 11 December 2024 (UTC)

This article says one knot is 1.2 MPH, which is true for the number of digits of precision stated. But in context of the claimed precision of 0.5% it would be more helpful to state that one knot is approximately 1.151 MPH. https://en.wikipedia.org/wiki/Knot_(unit) [[Special:Contributions/172.71.159.7|172.71.159.7]] 00:08, 12 December 2024 (UTC)

Transcendental : relating to a spiritual realm. eg "the transcendental importance of each person's soul". Works for me. {{unsigned ip|162.158.186.248|00:09, 12 December 2024 (UTC)}}

Just as a fun fact, "transcendental" in this case is referring to {{W|Transcendental number}}, which are numbers that cannot be expressed as the root of a polynomial, which basically means they cannot be found using algebra alone. I think the two definitions are related, since these numbers "trancend" the "realm" of numbers which can be found with algebra. [[Special:Contributions/172.68.22.82|172.68.22.82]] 01:04, 12 December 2024 (UTC)

Another maritime approximation: 1 meter/sec nearly equals 2 knots (actual is 1.94384), perhaps there is an actual explanation for this? {{unsigned ip|162.158.155.117|01:36, 12 December 2024 (UTC)}}

A better mnemonic, which I actually use: miles→km is Fibonacci. 2miles≈3km, 3miles≈5km, 5miles≈8km, 8miles≈13km, 13miles≈21km, 21miles≈34km, 34miles≈55km, 55miles≈89km, 89miles≈143.23km, Fibonacchi would predict 144km. But at that point, you can just remove some less significant digits anyway. For everything in between, you can estimate how far it is from the nearest Fibonacci numbers, that works pretty well, too. [[User:Fabian42|Fabian42]] ([[User talk:Fabian42|talk]]) 01:54, 12 December 2024 (UTC)
: Yes, similar to this comic the ratio of km to miles (1.6093) is very close to the golden ratio (1.6180) or (1 + sqrt(5))/2. [[Special:Contributions/172.68.54.64|172.68.54.64]] 04:28, 12 December 2024 (UTC)

3018: Second Stage

2024-12-01T18:45:34Z

172.68.54.64: /* Explanation */ but can be a problem in games such as :wikipedia:Kerbal Space Program|.

{{comic
| number = 3018
| date = November 29, 2024
| title = Second Stage
| image = second_stage_2x.png
| imagesize = 740x272px
| noexpand = true
| titletext = Hmm, they won't do in-flight delivery, so let's order a new first and second stage to our emergency landing site and then try to touch down on top of them to save time.
}}

==Explanation==
{{incomplete|Created by a BLUE ORIGIN DELIVERY DRIVER - Please change this comment when editing this page. Do NOT delete this tag too soon.}}

In this comic, two people have lifted off in a staged launch vehicle without their second stage installed. This is unlikely to happen in real life, because rocket launches are thoroughly planned and checked, and the lack of an entire stage would be glaringly obvious to anyone who is part of the project, but can be a problem in games such as [[:wikipedia:Kerbal Space Program|Kerbal Space Program]].

Staging in rocketry refers of the segmentation of a launch vehicle into distinct, separable modules, each one with an independent engine and fuel supply. This is practiced for two critical reasons: firstly, different engine designs work better at different altitudes, so you'd want to use one engine type deep in the atmosphere and a different engine once you get to space; and because, since you only need one of those engines at once, it'd be better to simply expend the first engine(s) and its fuel tank once you no longer need it. By getting rid of that useless mass, you can go farther using the same amount of fuel. A launch vehicle that does not employ staging is called an SSTO (Single-Stage-To-Orbit), but none of them have been successful due to the technical challenges.

As Pilot 1 calls to fire the second stage, Pilot 2 is initially confused and asks if a second stage was needed. Pilot 1 confirms that there was supposed to be a second stage, and thought that it was the Pilot 2's responsibility to install and confirm there was a second stage. When both pilots realize there is no second stage, Pilot 2, naturally, thinks he can order one on Amazon with same day delivery (though Amazon typically doesn't sell space ship stages - at least not with same day delivery [citation needed]). He then has difficulty picking an address zip code as they are likely traveling too high above the ground and too fast to be in a single postal area for long enough for the delivery to take place. The joke is likely poking fun at people who forget to pack certain items when going on road trips or vacation, and rely on Amazon to deliver replacements to them. There is also humor to be found in this rocket apparently being designed, built, and piloted by only two people-- in real life, the construction of a rocket, especially a manned one, involves thousands of people, and the pilots do not do the designing themselves.

The comic also alludes to a not-so-distant future when space travel is a much more mundane endeavor. If companies such as SpaceX succeed in their mass-production and launch cadence goals, one could imagine a scenario where rocket parts become standardized and easily replaceable-- similarly to how it is easy today to replace a car's tire or fill its fuel tank if you get stranded on a highway.

In the title text, Pilot 2 concludes that in-flight delivery won't be possible but proposes to have a new first and second stage delivered to their emergency landing site so they can pick them up and continue on their launch without stopping.

This is not the first time Randall discusses the idea of a mid-flight delivery. This [https://what-if.xkcd.com/149/ What If?] explanation attempts to answer if it possible to have pizza delivered to you, by a bird, while flying on a commercial airliner.

== Trivia ==
*The rocket, though apparently at least one segment short, appears to be substantially taller than the launch tower of the pad, which is a strangely incongruous detail. Unless the real rocket support is an angled back "hard spine" structure that has been rotated out of the way and down into the exhaust-flume/flame-trench quenching system. Since the voices are coming from what appears to be a separate module at the top of the rocket, it may be that the ''shell'' of the second stage is present, but not the engine and/or fuel.


==Transcript==
{{incomplete transcript|Do NOT delete this tag too soon.}}
:[A multi-stage rocket, with a capsule on top, is lifting-off the ground from a launchpad, at least two rocket nozzles are visibly producing a flame, and the pad is surrounded with smoke and/or steam from the blast suppression system. A voice comes from the capsule at the top.]
:We have liftoff.

:[The first stage separates from the rest of the rocket, part way through the roll-program. There are no obvious engines standing out from the 'second stage' (or extended payload trunk) lower shroud.]
:Main engine cutoff.
:Stage separation confirmed.
:We are go for second stage burn.

:Second stage?

:Yes.
:...What?

:[The first stage and the rest of the rocket are drifting apart in apparent freefall. No rocket is firing and the background does not seem to indicate that this view is beyond the atmosphere.]
:We were supposed to have a second stage?

:...Yes!

:Did '''''you''''' set up a second stage?

:I thought '''''you''''' were handling staging!

:Oh no.

:[They continue to drift apart slowly.]
:Okay, don't panic.
:Lemme see if we can order a stage online for same-day delivery.

:''Sigh''.

:Hey, what zip code should I put? Ours keeps changing.

{{comic discussion}}

[[Category:Space]]
[[Category:Rockets]]

Talk:3001: Temperature Scales

2024-10-22T00:02:02Z

172.68.54.64:

Shouldn't Rankine say "0ºR is set to absolute zero"? {{unsigned ip|172.70.230.29|22:58, 21 October 2024 (UTC)}}

yo,i thought comic 300 was anticlimactic so randall would make this one COOL but sadly not
Same. Hope he does something cool for 3072.[[Special:Contributions/172.69.134.225|172.69.134.225]] 23:44, 21 October 2024 (UTC)

really he didn't do anything special for this either? come ON randall if you don't do something cool for comic 3072 i will come to your house personally and yell at you [[User:RadiantRainwing|RadiantRainwing]] ([[User talk:RadiantRainwing|talk]]) 23:57, 21 October 2024 (UTC)

 
What's random about Fahrenheit? (Answer: nothing.) 0F is the freezing point of brine, 100F (or 98.7) is the human body temperature. [[Special:Contributions/172.68.54.65|172.68.54.65]] 00:00, 22 October 2024 (UTC)

Talk:2999: Bad Map Projection: The United Stralia

2024-10-16T19:49:27Z

172.68.54.64:

He forgot the Idaho abbreviation. [[User:Danger Kitty|Danger Kitty]] ([[User talk:Danger Kitty|talk]])
hello[[Special:Contributions/172.68.54.64|172.68.54.64]] 19:49, 16 October 2024 (UTC)

2984: Asteroid News

2024-09-12T01:33:53Z

172.68.54.64: Undo revision 350381 by 172.68.54.65 (talk)

{{comic
| number = 2984
| date = September 11, 2024
| title = Asteroid News
| image = asteroid_news_2x.png
| imagesize = 376x288px
| noexpand = true
| titletext = Their calculations show it will 'pass within the distance of the moon' but that it 'will not hit the moon, so what's the point?'
}}

==Explanation==
{{incomplete|Created by JUST A DEFINATLY BORING BOT LIKE ALL THE OTHER B̶̯͚͌͋O̶̟̎T̴̗̅̈́S̴̙̣̈́͊ - Please change this comment when editing this page. Do NOT delete this tag too soon.}}

This comic is about the recently discovered asteroid [https://www.esa.int/ESA_Multimedia/Images/2024/06/Close_approach_of_asteroid_2024_MK 2024 MK] that made a close approach to Earth on June 29 2024. The comic mentions that the asteroid only has a 'one-in-6000 chance of "doing something cool",' meaning that there is only a small chance that the asteroid will have a visible impact on {{w|Earth}}'s surroundings. What [[Blondie]] deems as "something cool" would presumably be the asteroid hitting Earth. The title text also mentions that the asteroid will also probably not hit the {{w|Moon}}, which is also another way for the asteroid to "do something cool." There is also a discrepancy with the image shown and actual predictions: the asteroid is expected to come within 0.75 lunar distances, inside the orbit of the Moon, while the comic shows the asteroid at least two {{w|lunar distances}} away from Earth.

Unlike almost all of [[Randall]]'s other comics, this one involves {{w|boredom}}.

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

:[Close-up of Blondie as a newscaster speaking, alongside an image to the left of an asteroid passing by Earth. The path of the asteroid is shown as a dashed line near the top-left, with the moon orbiting the earth below it.]
:Blondie: Astronomers initially said there was a one-in-6,000 chance that the newly-discovered asteroid might "do something cool" in 2063, but further observations determined it will be "Just a boring dot like all the others."

{{comic discussion}}

[[Category:Comics featuring Blondie]]
[[Category:News anchor]]
[[Category:Astronomy]]
[[Category:Space]]

Talk:2027: Lightning Distance

2018-08-06T15:01:53Z

172.68.54.64: more comments

Calculations I used:

<math>t_1=\frac{s}{v_1}</math>

<math>t_2=\frac{s}{v_2}</math>

Substract:

<math>t_1-t_2=\Delta t=\frac{s}{v_1}-\frac{s}{v_2}=\frac{sv_2-sv_1}{v_1v_2}=s\frac{v_2-v_1}{v_1v_2}=s\frac{\Delta v}{v_1v_2}</math>

Therefore

<math>s=\Delta t\frac{v_1v_2}{\Delta v}</math>

I evaluated <math>\frac{v_1v_2}{\Delta v}</math> and it came to be 13.6 billion. Can someone verify it's correct? [[Special:Contributions/172.68.51.112|172.68.51.112]] 13:08, 1 August 2018 (UTC)

:The comic begins with the question "how many miles away", so converting to kilometers isn't the right calculation.[[Special:Contributions/172.69.71.24|172.69.71.24]] 17:06, 1 August 2018 (UTC)

I used refractive index for visible light of 1.000277 (air at STP as opposed to 0C 1atm) and arrived at around 7.9 billion instead. Refractive index of 1.000337 is then required for the radio waves for the comic to be correct. [[Special:Contributions/172.68.11.221|172.68.11.221]] 13:46, 1 August 2018 (UTC)

:Do you mean 7.9 billion to convert to miles or to kilometers? Because my 13.6 bilion is to kilometers.

::I'm sure the actual comic is referring to miles and 5 billion was picked to match with the "divide by five" rule for miles. [[Special:Contributions/172.69.70.131|172.69.70.131]] 13:59, 1 August 2018 (UTC)

:::I did mean kilometers. If we use miles, 1.000314 fits almost precisely! (5.04 billion) [[Special:Contributions/172.68.11.17|172.68.11.17]] 14:42, 1 August 2018 (UTC)

If you can count several seconds, as is suggested in the comic, the flash is still billions of miles away, the widest possible distance between Earth and Neptune is about 5 billion km. Sebastian --[[Special:Contributions/172.68.110.40|172.68.110.40]] 14:51, 1 August 2018 (UTC)

:Not to mention that there's not a lot of air within a few billion miles of earth, so the dispersion will be much lower for all but the last 100-ish miles, AFAIK.[[Special:Contributions/172.68.54.142|172.68.54.142]] 20:12, 1 August 2018 (UTC)

::Also, while Jupiter has {{w|Great Red Spot|VERY gigantic storms}}, they are still too small to see the lightning from them from Earth. -- [[User:Hkmaly|Hkmaly]] ([[User talk:Hkmaly|talk]]) 23:17, 1 August 2018 (UTC)

Do you really need to know the spectrum of the flash? If we assume that a flash contains UV and X-ray radiation and that the visible light is generated at the same time as the UV or X-ray radiation then you only need to know the refractive index of light/UV/X-ray in air under the same temperature conditions and not the exact spectrum. [[User:Condor70|Condor70]] ([[User talk:Condor70|talk]])

:I initially made the mistake of thinking this referred to time difference between visible and UV/X-ray, but it specifically says "brightness." If you want to compare the brightness at a distance to the brightness at the source you'll need to know the brightness at the source, i.e. the spectrum of the flash itself. With this technique you don't need to know the dispersion "only" the relative attenuation, but I suspect that would be a more error-prone measurement.[[Special:Contributions/172.68.54.142|172.68.54.142]] 18:54, 1 August 2018 (UTC)

I understand the joke Randall was going for, but have a problem with the wording. "Count the number of seconds" won't work for fractions of anything. "Measure" would work, but spoils the gag a bit. Counting numbers are integers; counting the seconds between the visible and radio frequency flashes will give you zero. [[Special:Contributions/172.69.71.24|172.69.71.24]] 17:00, 1 August 2018 (UTC)

:You're certainly correct, but the joke works (for me at least) by its comparison to the standard rule of counting seconds, and humans are not generally precise enough to resolve better than one second. By keeping Megan's wording as close to the customary rule as possible I think it optimizes the humor. That "Billion" at the end is the whole joke for me, the replacement of "sound" with "radio wave" can be glossed-over on first reading, until you get to the unexpected extra 9 orders of magnitude in the conversion.[[Special:Contributions/172.68.54.142|172.68.54.142]] 18:54, 1 August 2018 (UTC)
::No, they would've been correct if she'd said "count the number of seconds" but she said "'''count the seconds'''".It's part of the joke, because it's correct, just completely impractical, because you'd be "counting" something like 10^(-10) seconds--[[Special:Contributions/172.68.132.47|172.68.132.47]] 07:23, 5 August 2018 (UTC)

::Just realized I also glossed-over the replacement of "divide" with "multiply." The brain is a funny thing.[[Special:Contributions/172.68.54.142|172.68.54.142]] 20:07, 1 August 2018 (UTC)

:I took the "count the number of seconds" to be part of the joke, or rather Randall setting us up for the joke. [[User:Redbelly98|Redbelly98]] ([[User talk:Redbelly98|talk]]) 02:18, 6 August 2018 (UTC)

Do these account for the air pressure variability common in most thunderstorms?

I think explanation and transcript are pretty complete now. [[Special:Contributions/172.68.51.112|172.68.51.112]] 20:58, 1 August 2018 (UTC)

:There is the additional problem that a flash is no instantaneous, but progresses at a fraction of the speed of light. Who says that radio waves and light at different wavelenghts or xrays have their maximum at the same moment? ;-) --[[Special:Contributions/162.158.91.59|162.158.91.59]] 08:05, 2 August 2018 (UTC)

:: I added a few words about the problem that a flash is not instantaneous and removed the 'incomplete' tag. Hope that's OK. [[User:Chrisahn|Chrisahn]] ([[User talk:Chrisahn|talk]]) 19:41, 2 August 2018 (UTC)

Here's a variation of the calculation above that simplifies numeric evaluation:

The {{w|refractive index}} is defined as <math>n=\frac{c}{v}</math>, so <math>v=\frac{c}{n}</math> and thus <math>t=\frac{s}{v}=\frac{s\,n}{c}</math>.

<math>t_1=\frac{s\,n_1}{c}</math>

<math>t_2=\frac{s\,n_2}{c}</math>

Subtract:

<math>t_1-t_2=\Delta t=\frac{s\,n_1}{c}-\frac{s\,n_2}{c}=s\frac{n_1-n_2}{c}=s\frac{\Delta n}{c}</math>

Therefore

<math>s=\Delta t\frac{c}{\Delta n}</math>

and the factor we want to calculate is

<math>\frac{c}{\Delta n}</math>

With the numbers given in the sources in the main text:

<math>n_1=1.000315</math>

<math>n_2=1.000277</math>

<math>\Delta n=n_1-n_2=0.000038</math>

For kilometers: <math>\frac{c}{\Delta n}\approx\frac{300,000\,km/s}{0.000038}\approx7.9\cdot10^9\,km/s</math>

For miles: <math>\frac{c}{\Delta n}\approx\frac{186,000\,mi/s}{0.000038}\approx4.9\cdot10^9\,mi/s</math>

[[User:Chrisahn|Chrisahn]] ([[User talk:Chrisahn|talk]]) 18:28, 2 August 2018 (UTC)

:Nice one. I didn't think to use the refractive indicies directly. [[Special:Contributions/172.68.51.118|172.68.51.118]] 22:22, 2 August 2018 (UTC)

:Agreed, nice clear analysis by Chrisahn. I'd like to suggest a couple of corrections regarding the index values:
:* ''n'' for air at 0 C, 1 atm, is closer to 1.000292, according to both {{w|List_of_refractive_indices|the Wikipedia link}} and also the "Simple Shop-floor Formula" given by NIST at [https://emtoolbox.nist.gov/wavelength/documentation.asp the bottom of this site]. This would give a <math>{\Delta n}</math> of 0.000023, and a time-to-distance conversion value of <math>\frac{c}{\Delta n} \approx 7.9\cdot10^9</math> mi/s.
:* Thunderstorms rarely occur at 0 C. Using values for 30 C (86 F) instead, we have 1.000261 for air (from the simple NIST formula) and 1.000429 for radio waves (from Table 1, p. 8 of [https://www.fig.net/resources/proceedings/fig_proceedings/fig_2002/Js28/JS28_rueger.pdf the Rueger paper]). This gives a <math>{\Delta n}</math> of 0.000168, and a time-to-distance conversion value of <math>\frac{c}{\Delta n} \approx 1.1\cdot10^9</math> mi/s.
:This suggests that the conversion value is the desired 5 billion for ''some'' temperature between 0 and 30 C. Linear interpolation of the above suggests this temperature is about 13 C or 55 F. More to the point, the conversion value varies too strongly with temperature for there to be a simple rule. That being said, I do like that the 5 billion figure ties in nicely with the familiar (in USA) ''divide by 5'' rule. [[User:Redbelly98|Redbelly98]] ([[User talk:Redbelly98|talk]]) 02:18, 6 August 2018 (UTC)

== Assumptions on the medium properties sound? ==

Refractive index of *dry* air might be pretty close to 1 for both light and RF EM waves, but:

Let's assume that the air is humid, if not even full of water drops. After all, lightning.

Let's further assume that an air/water mixture or solution has electromagnetic properties between these two materials.

In water, refractive index for light is about <math>n_{\text{water, optical}}=1.33 n_{\text{air, optical}}</math>, (as easily demonstrated by the optical refractive effects); for RF, we typically use values of <math>\frac{n_{\text{water, RF}}^2}{\mu_r}=\epsilon\approx 80</math>. So, <math>n_{\text{water, RF}}\approx \sqrt{80}n_{\text{air, RF}}</math>.

Let's assume a 10⁻³ "EM-effective" water content in the comic air.

That would lead to <math>\frac{v_{\text{opt.}}}{v_{\text{RF}}} = \frac{\frac34}{\sqrt{80}^{-1}}= \frac34\sqrt{80}=6.7</math>.

:While the humidity (amount of water vapor) is certainly higher during the rain, I don't think that would count as a proper "water-air mixture". Wikipedia says that "Violent rain" is above 5 cm/h. If you divide it by 3600 (to get cm/s), and then imagine stretching that all the way to the cloud, you'll find out there's not that much water at given moment in the air. [[Special:Contributions/172.68.51.112|172.68.51.112]] 19:12, 1 August 2018 (UTC)

::Great point. To finish the calculation let's use a typical terminal velocity for a large raindrop (it's a big storm, I'm sure) of 9m/s. 0.05 m/hr / 3600 s/hr / 9 m/s = 0.00015% water by volume. Sure seems like more than that when I have to drive through it! Then it seems more like [http://what-if.xkcd.com/12/].[[Special:Contributions/172.68.54.142|172.68.54.142]] 20:32, 1 August 2018 (UTC)

<code>we can't detect radiation outside the visible spectrum without very specialized instruments</code> Something that I think was overlooked in the explanation is that while humans can't *directly* sense radio waves, there are devices called "radios" which at one point in time were fairly commonly owned by humans, whose whole purpose is to detect encoded radio waves and convert them into sounds which humans can sense. I.e. you hear static during an electrical storm. So you could listen for the static and compare that to the flash... if you were fast enough. [[Special:Contributions/172.68.54.64|172.68.54.64]] 14:22, 3 August 2018 (UTC) (newbie)

:But radios ARE specialized equipment. [[Special:Contributions/172.68.51.52|172.68.51.52]] 10:35, 4 August 2018 (UTC)

::Ehh... I see your point, but I'm not sure I'm *really* convinced. In my mind, a Gamma Ray Spectrometer is specialized equipment. People don't normally have them in their house or car. Radios are (or, at least, *were*) very common. But you're right, it says specialized instrument, not "rare" instrument. I'm not changing the explanation, just wanted to point out for those geeky enough to read the comments that for normal people, *detecting* the radio wave output lightning is doable without buying extra equipment one doesn't normally have in the home. Detecting the difference between the flash and the static on the radio is where it gets impractical. [[Special:Contributions/172.68.54.64|172.68.54.64]] 15:01, 6 August 2018 (UTC) (newbie)

== Whoops! ==

I always thought it was 1 second per mile. I didn't know about the 'divide by 5" part. [[User:These Are Not The Comments You Are Looking For|These Are Not The Comments You Are Looking For]] ([[User talk:These Are Not The Comments You Are Looking For|talk]]) 01:23, 5 August 2018 (UTC)

:Storms just became 5 times more scary for you :) [[Special:Contributions/188.114.103.95|188.114.103.95]] 12:12, 6 August 2018 (UTC)

Talk:2027: Lightning Distance

2018-08-03T14:22:57Z

172.68.54.64: something possibly overlooked in explanation

Calculations I used:

<math>t_1=\frac{s}{v_1}</math>

<math>t_2=\frac{s}{v_2}</math>

Substract:

<math>t_1-t_2=\Delta t=\frac{s}{v_1}-\frac{s}{v_2}=\frac{sv_2-sv_1}{v_1v_2}=s\frac{v_2-v_1}{v_1v_2}=s\frac{\Delta v}{v_1v_2}</math>

Therefore

<math>s=\Delta t\frac{v_1v_2}{\Delta v}</math>

I evaluated <math>\frac{v_1v_2}{\Delta v}</math> and it came to be 13.6 billion. Can someone verify it's correct? [[Special:Contributions/172.68.51.112|172.68.51.112]] 13:08, 1 August 2018 (UTC)

:The comic begins with the question "how many miles away", so converting to kilometers isn't the right calculation.[[Special:Contributions/172.69.71.24|172.69.71.24]] 17:06, 1 August 2018 (UTC)

I used refractive index for visible light of 1.000277 (air at STP as opposed to 0C 1atm) and arrived at around 7.9 billion instead. Refractive index of 1.000337 is then required for the radio waves for the comic to be correct. [[Special:Contributions/172.68.11.221|172.68.11.221]] 13:46, 1 August 2018 (UTC)

:Do you mean 7.9 billion to convert to miles or to kilometers? Because my 13.6 bilion is to kilometers.

::I'm sure the actual comic is referring to miles and 5 billion was picked to match with the "divide by five" rule for miles. [[Special:Contributions/172.69.70.131|172.69.70.131]] 13:59, 1 August 2018 (UTC)

:::I did mean kilometers. If we use miles, 1.000314 fits almost precisely! (5.04 billion) [[Special:Contributions/172.68.11.17|172.68.11.17]] 14:42, 1 August 2018 (UTC)

If you can count several seconds, as is suggested in the comic, the flash is still billions of miles away, the widest possible distance between Earth and Neptune is about 5 billion km. Sebastian --[[Special:Contributions/172.68.110.40|172.68.110.40]] 14:51, 1 August 2018 (UTC)

:Not to mention that there's not a lot of air within a few billion miles of earth, so the dispersion will be much lower for all but the last 100-ish miles, AFAIK.[[Special:Contributions/172.68.54.142|172.68.54.142]] 20:12, 1 August 2018 (UTC)

::Also, while Jupiter has {{w|Great Red Spot|VERY gigantic storms}}, they are still too small to see the lightning from them from Earth. -- [[User:Hkmaly|Hkmaly]] ([[User talk:Hkmaly|talk]]) 23:17, 1 August 2018 (UTC)

Do you really need to know the spectrum of the flash? If we assume that a flash contains UV and X-ray radiation and that the visible light is generated at the same time as the UV or X-ray radiation then you only need to know the refractive index of light/UV/X-ray in air under the same temperature conditions and not the exact spectrum. [[User:Condor70|Condor70]] ([[User talk:Condor70|talk]])

:I initially made the mistake of thinking this referred to time difference between visible and UV/X-ray, but it specifically says "brightness." If you want to compare the brightness at a distance to the brightness at the source you'll need to know the brightness at the source, i.e. the spectrum of the flash itself. With this technique you don't need to know the dispersion "only" the relative attenuation, but I suspect that would be a more error-prone measurement.[[Special:Contributions/172.68.54.142|172.68.54.142]] 18:54, 1 August 2018 (UTC)

I understand the joke Randall was going for, but have a problem with the wording. "Count the number of seconds" won't work for fractions of anything. "Measure" would work, but spoils the gag a bit. Counting numbers are integers; counting the seconds between the visible and radio frequency flashes will give you zero. [[Special:Contributions/172.69.71.24|172.69.71.24]] 17:00, 1 August 2018 (UTC)

:You're certainly correct, but the joke works (for me at least) by its comparison to the standard rule of counting seconds, and humans are not generally precise enough to resolve better than one second. By keeping Megan's wording as close to the customary rule as possible I think it optimizes the humor. That "Billion" at the end is the whole joke for me, the replacement of "sound" with "radio wave" can be glossed-over on first reading, until you get to the unexpected extra 9 orders of magnitude in the conversion.[[Special:Contributions/172.68.54.142|172.68.54.142]] 18:54, 1 August 2018 (UTC)

::Just realized I also glossed-over the replacement of "divide" with "multiply." The brain is a funny thing.[[Special:Contributions/172.68.54.142|172.68.54.142]] 20:07, 1 August 2018 (UTC)

Do these account for the air pressure variability common in most thunderstorms?

I think explanation and transcript are pretty complete now. [[Special:Contributions/172.68.51.112|172.68.51.112]] 20:58, 1 August 2018 (UTC)

:There is the additional problem that a flash is no instantaneous, but progresses at a fraction of the speed of light. Who says that radio waves and light at different wavelenghts or xrays have their maximum at the same moment? ;-) --[[Special:Contributions/162.158.91.59|162.158.91.59]] 08:05, 2 August 2018 (UTC)

:: I added a few words about the problem that a flash is not instantaneous and removed the 'incomplete' tag. Hope that's OK. [[User:Chrisahn|Chrisahn]] ([[User talk:Chrisahn|talk]]) 19:41, 2 August 2018 (UTC)

Here's a variation of the calculation above that simplifies numeric evaluation:

The {{w|refractive index}} is defined as <math>n=\frac{c}{v}</math>, so <math>v=\frac{c}{n}</math> and thus <math>t=\frac{s}{v}=\frac{s\,n}{c}</math>.

<math>t_1=\frac{s\,n_1}{c}</math>

<math>t_2=\frac{s\,n_2}{c}</math>

Subtract:

<math>t_1-t_2=\Delta t=\frac{s\,n_1}{c}-\frac{s\,n_2}{c}=s\frac{n_1-n_2}{c}=s\frac{\Delta n}{c}</math>

Therefore

<math>s=\Delta t\frac{c}{\Delta n}</math>

and the factor we want to calculate is

<math>\frac{c}{\Delta n}</math>

With the numbers given in the sources in the main text:

<math>n_1=1.000315</math>

<math>n_2=1.000277</math>

<math>\Delta n=n_1-n_2=0.000038</math>

For kilometers: <math>\frac{c}{\Delta n}\approx\frac{300,000\,km/s}{0.000038}\approx7.9\cdot10^9\,km/s</math>

For miles: <math>\frac{c}{\Delta n}\approx\frac{186,000\,mi/s}{0.000038}\approx4.9\cdot10^9\,mi/s</math>

[[User:Chrisahn|Chrisahn]] ([[User talk:Chrisahn|talk]]) 18:28, 2 August 2018 (UTC)

:Nice one. I didn't think to use the refractive indicies directly. [[Special:Contributions/172.68.51.118|172.68.51.118]] 22:22, 2 August 2018 (UTC)

== Assumptions on the medium properties sound? ==

Refractive index of *dry* air might be pretty close to 1 for both light and RF EM waves, but:

Let's assume that the air is humid, if not even full of water drops. After all, lightning.

Let's further assume that an air/water mixture or solution has electromagnetic properties between these two materials.

In water, refractive index for light is about <math>n_{\text{water, optical}}=1.33 n_{\text{air, optical}}</math>, (as easily demonstrated by the optical refractive effects); for RF, we typically use values of <math>\frac{n_{\text{water, RF}}^2}{\mu_r}=\epsilon\approx 80</math>. So, <math>n_{\text{water, RF}}\approx \sqrt{80}n_{\text{air, RF}}</math>.

Let's assume a 10⁻³ "EM-effective" water content in the comic air.

That would lead to <math>\frac{v_{\text{opt.}}}{v_{\text{RF}}} = \frac{\frac34}{\sqrt{80}^{-1}}= \frac34\sqrt{80}=6.7</math>.

:While the humidity (amount of water vapor) is certainly higher during the rain, I don't think that would count as a proper "water-air mixture". Wikipedia says that "Violent rain" is above 5 cm/h. If you divide it by 3600 (to get cm/s), and then imagine stretching that all the way to the cloud, you'll find out there's not that much water at given moment in the air. [[Special:Contributions/172.68.51.112|172.68.51.112]] 19:12, 1 August 2018 (UTC)

::Great point. To finish the calculation let's use a typical terminal velocity for a large raindrop (it's a big storm, I'm sure) of 9m/s. 0.05 m/hr / 3600 s/hr / 9 m/s = 0.00015% water by volume. Sure seems like more than that when I have to drive through it! Then it seems more like [http://what-if.xkcd.com/12/].[[Special:Contributions/172.68.54.142|172.68.54.142]] 20:32, 1 August 2018 (UTC)

Something that I think was overlooked in the explanation is that while humans can't *directly* sense radio waves, there are devices called "radios" which at one point in time were fairly commonly owned by humans, whose whole purpose is to detect encoded radio waves and convert them into sounds which humans can sense. I.e. you hear static during an electrical storm. So you could listen for the static and compare that to the flash... if you were fast enough. [[Special:Contributions/172.68.54.64|172.68.54.64]] 14:22, 3 August 2018 (UTC) (newbie)

Talk:1930: Calendar Facts

2017-12-18T18:00:25Z

172.68.54.64:

Shouldn't it be "libration" not "libation"? Pretty sure drinking has nothing to do with it. Also pretty sure this is a mistake and not a clever alteration. [[Special:Contributions/162.158.62.57|162.158.62.57]] 16:41, 18 December 2017 (UTC)
:No, it's a clever alteration because "libration" is listed right above it. --[[User:Videblu|Videblu]] ([[User talk:Videblu|talk]]) 16:45, 18 December 2017 (UTC)
::That's just a mistake - he meant to write 'vibration'[[Special:Contributions/141.101.76.16|141.101.76.16]] 16:48, 18 December 2017 (UTC)
:::'Vibration' wouldn't make any sense, 'libation' is at least humorous, I vote it was no mistake. [[Special:Contributions/172.68.54.64|172.68.54.64]] 18:00, 18 December 2017 (UTC)

1916: Temperature Preferences

2017-11-15T06:18:08Z

172.68.54.64: /* Explanation */

{{comic
| number = 1916
| date = November 15, 2017
| title = Temperature Preferences
| image = temperature_preferences.png
| titletext = There's a supposed Mark Twain quote, "The coldest winter I ever spent was a summer in San Francisco." It isn't really by Mark Twain, but I don't know who said itâI just know they've never been to McMurdo Station.
}}

==Explanation==
{{incomplete|Edited by GLOBAL WARMING - Please change this comment when editing this page. Do NOT delete this tag too soon.}}
This is a chart of major (and not-so-major) populated areas showing seasonal temperature patterns. The chart is a guide to where one might like to live depending on how much summer heat and winter cold they enjoy. There are four focused zones:

* Hate both cold and heat (eg. Quito, Addis Ababa)--Neither summers nor winters are too extreme
* Hate cold but love heat (eg. Rio, Bangkok, Manila)--Tropical regions, very hot in the summer
* Hate heat but love cold (eg. Moscow, Oslo)--High latitudes, very cold in the winter
* Love both heat and cold (eg. Seoul, Beijing)--Both summers and winters are too extreme

The summer heat axis is determined by {{w|humidex}}, a system that combines heat and humidity to generate an estimate of perceived "summer discomfort".

It is unclear for how long the chart will stay accurate under {{w|climate change}}. As winters and summers become more extreme, many cities may move to the "love both" area.

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

{{comic discussion}}

1910: Sky Spotters

2017-11-03T02:23:22Z

172.68.54.64:

{{comic
| number = 1910
| date = November 1, 2017
| title = Sky Spotters
| image = sky_spotters.png
| titletext = Where I live, one of the most common categories of sky object without a weird obsessive spotting community is "lost birthday party balloons," so that might be a good choice—although you risk angering the marine wildlife people, and they have sharks.
}}

==Explanation==
This comic explores how people with various hobbies notice strange things in the sky.

In first panel the plane enthusiasts [[White Hat]] and [[Hairy]] notice that there is a {{w|Piper PA-24 Comanche}} in the sky (apparently the most recent of several), belonging to a holding company that has filed no flight plans. Flight plans do not need to be filed for many short flights at lower altitudes in good weather, so for a small aircraft like the PA-24 the missing flight plan alone should not be unusual. Many government or company planes used for secret purposes, like [https://www.buzzfeed.com/peteraldhous/hidden-spy-planes FBI planes registered to fake companies], go a step further and are blacklisted from major databases. Regardless, it makes White Hat and Hairy wonder why, enough that they decide to post about it on their {{w|Aircraft spotting|plane spotter}} forums. (See [[1669: Planespotting]]).

In the second panel [[Hairbun]] and a male bird enthusiast are wondering why there is a {{w|broad-winged hawk}} in the area in November, when many broad-winged hawks should have migrated south to areas like Florida and Central America. They decide to send a message to their {{w|birdwatching}} e-mail list. (See [[1824: Identification Chart]] and [[1826: Birdwatching]]). The two birdwatchers in this panel look like the old version of [[Cueball]] and [[Megan]] in [[572: Together]].

In the last panel, a committee from what appears to be the {{w|National Security Agency}} wonders how to disguise their {{w|Unmanned aerial vehicle|drones}} so that people will not pay attention to them. The boss at the end of table is lamenting the fact that both their bird- and plane-disguised drones have been noticed because of all these people constantly checking out the sky, also indicating that there are even more subcultures who are obsessed with things in the sky than the two mentioned already. [[Ponytail]] asks what else they could disguise their (secret) surveillance drones as, and Cueball suggests a {{w|weather balloon}}. But Ponytail shoots this down since such a disguise would attract both the {{w|UFO}} enthusiasts and the "weather people". A joke is then put in as she notes that she doesn't know which is worse. Since most people consider UFO enthusiasts to be in to conspiracies, the "weather people" may be annoyed by this. Maybe [[Randall]] is indicating that people trying to predict the weather are correct as often as those claiming to have seen a UFO...

There are numerous instances of weather balloons being labeled as UFOs by enthusiasts, one of the most notable being the {{w|Roswell UFO incident}}, which for years was explained by the US military as a weather balloon crash, but turned out to be a nuclear test surveillance balloon. It is now known as the ''most thoroughly debunked UFO claim''.

In the title text it is suggested that "lost birthday party balloons" should not attract too much attention. But then it is noted that it might make marine wildlife people angry, their concern probably being that balloons ultimately end up in some water body, which causes marine wildlife to get trapped in plastic and other synthetic material that was dumped in the water. (see {{w|Marine debris}}) "Marine wildlife people with sharks" may be a reference to [[585: Outreach]], which also features a balloon carrying a shark. Another possible issue with disguising drones as "lost balloons" is that such balloons are quite rarely seen, and a sudden increase in the number of "lost balloons" seen would certainly raise suspicion even without a "spotting community" that focuses on them.

The reference to red trim on the Piper PA-24 Comanche could be a reference to the livery of {{w|Janet (airline)}} which operates clandestine flights between Las Vegas, Area 51, and other desert military bases, although these planes are in fact registered to the Department of the Air Force, rather than a holding company.

Among other types of people looking at the sky, the comic doesn't even get around to mentioning the subject of comic [[1644: Stargazing]].

==Transcript==
:[White Hat and Hairy are standing in front of some buildings. White Hat points to the sky while holding his smartphone in the other hand, while Hairy holds his smartphone up in both hands as he looks at the screen.]
:White Hat: That's odd—another PA-24 Comanche with red trim. Registered to a holding company, no recent flight plans.
:Hairy: I'll ask the forums if anyone knows who operates those.

:[Hairbun and an old man with white sailor cap, are standing in a field with rolling hills behind them. Hairbun is looking at the sky through her binoculars, that she has in a string around her neck. The man also looks up but he is holding his string attached binoculars down in front of him.]
:Hairbun: Goodness, I think that's a broad-winged hawk!
:Man with sailor cap: In November?! They should be long gone by now!
:Hairbun: I'll email the list.

:[Five people sit around a table in a boardroom, which presumably belongs to the government as the table has a circular insignia with an eagle in the center and unreadable text in the ring around the eagle and beneath the insignia. A man with slick black hair is sitting at the end of the table in an office chair. The other four are sitting behind the long side of the table; from left they are Cueball, Megan, another version of Hairy with spikier hair, and to the right, Ponytail.]
:Man at the end of the table: Dammit, why are there so many different subcultures obsessed with staring at the sky?
:Ponytail: What else could we disguise our surveillance drones as?
:Cueball: Weather balloons?
:Ponytail: No, that gets the UFO people ''and'' the weather people.
:Ponytail: Don't know who's worse.

{{comic discussion}}

[[Category:Comics featuring White Hat]]
[[Category:Comics featuring Hairy]]
[[Category:Comics featuring Hairbun]]
[[Category:Comics featuring Cueball]]
[[Category:Comics featuring Megan]]
[[Category:Comics featuring Ponytail]]
[[Category:Drones]]
[[Category:Animals]]

1300: Galilean Moons

2017-08-29T20:30:15Z

172.68.54.64: /* Explanation */

{{comic
| number = 1300
| date = December 6, 2013
| title = Galilean Moons
| image = galilean_moons.png
| titletext = I'm SO glad I escaped. They almost had me caught in their weird ...thing.
}}

==Explanation==
[[File:Galilean moon Laplace resonance animation.gif|thumb|365px|The 1:2:4 {{w|orbital resonance}} of {{w|Ganymede (moon)|Ganymede}}, {{w|Europa (moon)|Europa}}, and {{w|Io (moon)|Io}}]] 

Megan has somehow acquired a set of {{w|Galilean moons}} similar to the four primary moons of {{w|Jupiter}}. The positions of the moons in the successive panels are reminiscent of the observations made by {{w|Galileo Galilei|Galileo Galilei}} in 1610, which proved for the first time that objects in the heavens could orbit something other than the Earth (today these observations can be reproduced on successive nights by anyone looking at Jupiter with binoculars). As each of Megan's moons passes close to Cueball, it says something different. {{w|Io (moon)|Io}}, the innermost and second-smallest, always says "Hi!" {{w|Europa (moon)|Europa}}, the second-innermost and smallest, always uses the phrase "What's your name?" {{w|Ganymede (moon)|Ganymede}}, the third moon from Jupiter but the largest in size, interrupts Europa by shouting "MOOOOOON!" Callisto, the farthest from Megan, expresses its annoyance at the antics of the other three moons. ("MOOOOOOON!" might be a reference to an old joke: Q: Knock Knock. A: Who's there? Q: Interrupting Cow. A: Interrupting Co-- Q: MOOOOOOO!)

Because the inner moons orbit Jupiter faster (due to {{w|Kepler's laws of planetary motion#Third law|Kepler's Third Law}}), they pass by Cueball more often: Io ten times, Europa five times, and Ganymede twice over the course of the comic. In fact, the outermost crater-scarred moon {{w|Callisto (moon)|Callisto}} appears to have passed its closest approach to Cueball just before the first panel (perhaps before Megan and her retinue had walked up to Cueball) and does not approach Cueball again until the tenth panel. At that point, due to some apparent exertion on Callisto's part, it leaves Megan's orbit and begins to orbit Cueball instead. This process could be seen as analogous to the capture of moons from one planet to another, which can happen in less stable systems than our solar system if two planets were to pass close to each other, but is mostly just whimsical. The humour derives from attributing human characteristics to the moon Callisto in attempting to escape from the other three moons.

The title text refers to the unusual {{w|orbital resonance}} among the three inner Galilean moons: Io has an orbital period of about 1.78 Earth days, Europa 3.55 days, and Ganymede 7.15 days, putting them into a 1:2:4 resonance. Callisto, with an orbital period of 16.69 days, is not part of the resonant system. This is illustrated in the animated picture at right, where you may notice that all conjunctions between Io and Europa take place at the "12 o'clock" position and all conjunctions between Europa and Ganymede take place at "6 o'clock" position. You may also notice at the animated picture that, unlike in the fifth and ninth panels of the comic, the three moons are never on the same side of Jupiter at the same time. It is thought that this resonance came about as the moons migrated outward due to {{w|tidal acceleration}}; because the inner moons migrated more quickly, first Io caught up with the 2:1 resonance with Europa and then the two of them evolved outward in lockstep until Europa caught up with the 2:1 resonance with Ganymede. If the Jupiter system were to continue its current evolutionary path for long enough (several billion years), Ganymede would eventually catch up to the 2:1 resonance with Callisto and Callisto would also be trapped in the resonance, becoming the fourth member of a 1:2:4:8 system. The title text expresses Callisto's relief at escaping such a fate, describing the relationship among the other three moons as "their weird ...thing." Callisto also escapes a common practice among certain groups of humans in which the members greet each other with meaningless phrases, usually an inside joke, whenever they meet, which could also be described as "their weird ...thing." The word "orbit" could finish Callisto's sentence, as it can also mean a sphere of influence or interest.

==Transcript==
:[Megan approaches Cueball, orbited by four small floating balls.]
:Megan: Check it out!
:Cueball: What?
:Megan: I've got Galilean moons!

:[Io is at the point in its orbit closest to Cueball.]
:Io: Hi!

:[Io, which completes a full orbit in each panel, is again near Cueball, as is Europa this time.]
:Io: Hi!
:Europa: What's your name?

:[Io alone again.]
:Io: Hi!

:[Europa returns to its position near Cueball with Io, and Ganymede joins them.]
:Io: Hi!
:Europa: What's your—
:Ganymede: '''''MOOOOOON!'''''

:[Io alone again.]
:Io: Hi!

:[Europa and Io again.]
:Io: Hi!
:Europa: What's your name?
:Callisto: [on the other side of Megan] ''Ugh''.

:[Io alone again.]
:Io: Hi!
:Callisto: ''So annoying''.

:[Europa, Ganymede, and Io again.]
:Io: Hi!
:Europa: What's y—
:Ganymede: '''''MOOOOOON.'''''

:[Io alone again. Callisto nudges toward Cueball.]
:Io: Hi!
:Callisto: ...''almost''... ...''almoooost''...

:[Io and Europa again. Callisto enters an orbit around Cueball.]
:Io: Hi!
:Europa: What's your name?
:Callisto: ''Yessss!''

{{clear}}
{{comic discussion}}
[[Category:Comics featuring Cueball]]
[[Category:Comics featuring Megan]]
[[Category:Astronomy]]

1818: Rayleigh Scattering

2017-03-31T22:56:10Z

172.68.54.64: I see no reason to assume that Blondie is the mother of the questioner here? She might be; Megan might be; both might be; or neither might be. The comic doesn't seem to give any reason to favor any one hypothesis.

{{comic
| number = 1818
| date = March 31, 2017
| title = Rayleigh Scattering
| image = rayleigh_scattering.png
| titletext = If you ask "why are leaves green?" the usual answer is "because they're full of chlorophyll, and chlorophyll is green," even though "why does chlorophyll scatter green light?" is a great question too.
}}

==Explanation==
{{incomplete|Incomplete explanation Needs fixing upping. DO NOT DELETE}}

This comic suggests it is much better to explain things in an easy-to-understand and intuitive manner, even if such explanations may not be completely accurate. This is especially the case for children whose ability to grasp abstract physics has not yet fully developed. Giving the most complete and physically accurate explanation would make the concepts much more elaborate than necessary, and would cause major confusion in inexperienced listeners.

The principle is demonstrated by the explanation on {{w|Diffuse sky radiation|why the sky is blue}}. The commonly given explanation for this is, as the comic title says, {{w|Rayleigh scattering}}. However, in order to understand how Rayleigh scattering works to produce a blue color, one must go into {{w|quantum mechanics}} and deal with properties of molecules in air and their effects on different wavelengths of light. Even then, one will also need to know about the inner workings of human visual perception to realize why the color we perceive isn't the wavelength that's being most strongly scattered (see [[1145: Sky Color]]). The child is not likely to understand this kind of explanation.

On the other hand, a much simpler explanation, such as "because air is blue", also adequately explains the phenomenon, and is probably much more understandable to less physically inclined listeners. When a person who looks like a young [[Science Girl]] asks [[Blondie]] why is the sky blue, [[Megan]] walks in and starts to explain in a very scientific way. This is criticized by Blondie, who then convinces her that the simpler explanation is sufficient, as there is a quantum mechanical explanation for every color, there is no need to elaborate on the sky's color any more than any other object's color.

The last panel takes this explanation to the extreme by claiming that aeroplanes stay up because they have thousands of birds in their wings that hold them up by flapping. This, while certainly easier to understand, is much farther from reality than the explanation in the previous panels. Even this is not as farfetched as it may first appear. For example, in most current grade school curriculums, children are taught that atoms are made of a central nucleus with electrons orbiting around it like planets orbit around the sun. This is also an extremely simplified and inaccurate model in light of quantum mechanics. Nevertheless, it is taught as fact at least until the children are ready to take on the more complete explanation. The child's reaction in this comic, "Wow!", suggests that not only she understood, but is also excited about learning, which could be more important to her development than hearing the "correct" answer up front.

The title text refers to another common question as for why leaves are green. This is commonly explained by the fact that they are filled with {{w|chlorophyll}}, a chemical used by plants for photosynthesis. Randall points out that it would be an equally valid question to ask why chlorophyll is green. This poses an interesting contrast to the answer to the question about the color of the sky, since even physicists are usually satisfied with the general explanation for leaves and don't feel the need to jump into describing quantum phenomena that cause chlorophyll to reflect green light. Also, "Why does chlorophyll scatter green light" may be a great question because chlorophyll reflects, not scatters, light and this challenges Megan-types to coherently explain the difference before they go challenging little children with pedantry.

[https://what-if.xkcd.com/141/ What-if 141] also mentions the simpler explanation to the original question: Sunbeam has this relevant text: "Normal light interacts with the atmosphere through Rayleigh scattering. You may have heard of Rayleigh scattering as the answer to 'why is the sky blue.' This is sort of true, but honestly, a better answer to this question might be 'because air is blue.' Sure, it appears blue for a bunch of physics reasons, but everything appears the color it is for a bunch of physics reasons." There is also a footnote in that comment with an additional example: "When you ask, 'Why is the {{w|Statue of Liberty|statue of liberty}} green?' the answer is something like, 'The outside of the statue is copper, so it used to be copper-colored. Over time, a layer of copper carbonate formed (through oxidation), and copper carbonate is green.' You don't say 'The statue is green because of frequency-specific absorption and scattering by surface molecules.' "

==Transcript==

:[Young Science Girl and Blondie are talking.]
:Science Girl: Why is the sky blue?
:Blondie: Because air is blue.

:[Megan walks in.]
:Megan: No, the sky is blue because of Rayleigh scattering–
:Blondie: Nah, it's because air is blue. Blue light bounces off it and hits our eyes. Same as why anything is any color.

:[Zoom in on Blondie.]
:Blondie: It's why far-off mountains look blue – because of all the blue air in the way.

:[Back to view of three characters.]
:Megan: There's a specific quantum mechanism by which–
:Blondie: Yeah but there's a physics mechanism for every color. You don't have to get all quantum right away.

:[Frameless panel with Blondie and Science Girl.]
:Megan (off-panel): ...OK, I guess.
:Blondie: Any other questions?
:Science Girl: How do planes stay up?

:[Back to all three characters.]
:Megan: Well, the airflow–
:Blondie: Tiny birds in the wings. Thousands. Flapping Hard.
:Science Girl: WOW!
:Megan: ''NO!''

{{comic discussion}}

[[Category:Comics featuring Science Girl]]
[[Category:Comics featuring Blondie]]
[[Category:Comics featuring Megan]]

596: Latitude

2017-03-08T16:17:46Z

172.68.54.64: /* Trivia */ Fixed typo

{{comic
| number = 596
| date = June 12, 2009
| title = Latitude
| image = latitude.png
| titletext = The G1, especially with the new Android upgrade, is way better than I originally thought.
}}

==Explanation==

[[Black Hat]] shows his friend [[Cueball]] that he has made a mobile phone application to log and find addresses and business names for the locations of his "friends" using data from {{w|Google Latitude}} which was a location-aware feature of Google Maps that allowed a mobile phone user to allow certain people to view their current location.

The reason it is worth doing so for him, is that most of those that use Google Latitude, haven't learned the habit to turn it off when engaging in "discreet" activities. And then Black Hat can access their whereabout which he then uses in his app.

The second panel shows the screen of Black Hat's smartphone with the logs for his two friend in table form showing activity for [[Megan]] and Robert, the latter log is partially cut off. (Regarding the use of these names see the [[#Trivia|trivia section]]).

Robert's log is fairly innocuous: home at 12:30 PM, school at 2:00 PM and in a {{w|Subway (restaurant)|Subway restaurant}} at 3:30 PM. This log shows that Robert did nothing interesting for Black Hat. There are also several holes in the table compared to the other column. This could either indicate that he stayed this long time those three places, but it could also indicate that Robert has already learned to switch off Latitude when he is not actively using it. This would fit with Black Hat's comment about a narrow window in which people haven't learned this. His friend Robert (which could be the Cueball shown here, see the [[#Trivia|trivia section]]), may already have thought of this himself, or maybe Black Hat has mentioned it to him before getting the idea for the app thus warning him about the problem (without meaning to).

The reason Black Hat states that there only is a ''narrow window of time that people forget to turn Google Latitude off'', is because people like him will make other people, who forgets this, miserable. And then everyone will soon learn to turn the feature off making Black Hat's app useless.

Megan's log appears to prove Black Hat's point: She was home at 11:00 AM, at a {{w|sex toy}} store at 12:30 PM, home again at 1:30 PM, at another sex toy store at 2:00 PM, home again at 2:30 PM, then at {{w|Fry's Electronics}} at 3:00 PM, and directly at a {{w|power tool}} store at 3:30 PM, finally home again at 4:00 PM only to be at the hospital burn ward at 4:10 PM. The last entry is the only one where the interval is not half an hour indicating how fast Megan had to get to the hospital after getting home with her new power tools and electronics (note that Fry is a name, as in Charles Fry, so this was not why she was fried...)

This suggests that Megan first tried the sex toy(s) from the first store, found them insufficiently satisfying, purchased additional sex toys from another store, was still unsatisfied, and then purchased some electronic devices and power tools (either to improve the performance of her sex toys or to apply directly for additional stimulation). The results were apparently more painful than pleasurable, necessitating a quick visit to the hospital burn ward. Overall, Megan has had an at first unsatisfying day and then finally a rather bad day, considering where the burn is most likely to be... She would almost certainly not be pleased to learn that Black Hat has been tracking her whereabouts and sharing this with their mutual friend Cueball.

The title text shows that [[Randall]] liked the T-Mobile G1, also known as the {{w|HTC Dream}}, especially with the new Android upgrade, more than he previously thought because it allows for more capabilities and the interface is clean and easy-to-use when compared to other "smartphones" of that time period (because the G1 was the first phone to introduce {{w|Android}}) and it allows for special Google networking, allowing for apps like Maps to run better (making it easier to run apps like Latitude). From what able to be gathered in the comic, it is [[Black Hat]] who says this, because he is the one who uses the app and shows it off to [[Randall]]. He would be the most likely one to benefit from this kind of phone running this kind of OS/app.

==Transcript==
:[Black Hat is holding a phone up to Cueball.]
:Black Hat: We're in a narrow window in which people are using Google Latitude, but haven't learned the habit of turning it off when they're doing something discreetly.
:Black Hat: I wrote an app to log friends' locations and work out addresses and business names.

:[A timetable is visible. The first column gives the time and splits the day in the half hour intervals starting at 11:00 AM, except for the last entry at 4:10 PM, where the time only jumps 10 minutes. The next two columns represents two persons activities during this time period. In the second column the last letter shown in the comic is partly cut off more or less. This last partly shown letter is written in the transcript, but no guess is made here. See the explanation. Above the table, over the two names, there is a caption:]
:::::<big>Locations</big>
:{| class="wikitable"
|-
|Time ||Megan ||Rober
|-
|11:00 AM || Home ||
|-
|12:30 PM || Eastview Adult Toy Store || Home
|-
|1:30 PM || Home ||
|-
|2:00 PM || Laketown Sex Toy Shop || Schoo
|-
|2:30 PM ||Home ||
|-
|3:00 PM || Fry's Electronics ||
|-
|3:30 PM || Ed's Power Tool Emporium || Subwa
|-
|4:00 PM || Home ||
|-
|4:10 PM || Hospital Burn Ward ||
|}

==Trivia==
*This is one of the handful of times that the name ''Megan'' has been used in xkcd, in this case without actually showing Megan, so there is actually no indication in this comic how she looks. But that has been shown in several others.
**Despite her not being shown, the comic should be listed as featuring Megan, as her name is used.
*Given that Black Hat has sometimes interacted with the Cueball called [[Rob]], it seems likely that the Cueball in this comic is actually Rob (for Robert), and it turns out that he has either forgotten to turn off his Google Latitude, or only has it turned on when he actually uses it. He has in either case only used it in inconspicuous places, and would not be alarmed at seeing the table of his own activities.
**Maybe this is why Black Hat shows it to him, so he can share Megan's event log which is much more interesting.
**That Rob has been at a school could mean he was a teacher or for some other reason needed to go there. It is such a short time span in the afternoon that it does not seem like something a school kid would do.
***Some have, using the school as argument, suggested that this Robert is actually [[Little Bobby Tables]].
***But Black Hat has never interacted with the [[Mrs. Roberts|Roberts family]] so this seems unlikely, and he has never been called Robert, but he has been drawn like a kid looking like Cueball.
**Given that it is unclear if it is either Rob or Bobby neither should be credited as part of this comic.

{{comic discussion}}

[[Category:Comics featuring Cueball]]
[[Category:Comics featuring Black Hat]]
[[Category:Comics featuring Megan]]
[[Category:Comics featuring Rob]]
[[Category:Smartphones]]
[[Category:Charts]]
[[Category:Sex]]

596: Latitude

2017-03-08T16:14:12Z

172.68.54.64: /* Explanation */ Fixed typo

{{comic
| number = 596
| date = June 12, 2009
| title = Latitude
| image = latitude.png
| titletext = The G1, especially with the new Android upgrade, is way better than I originally thought.
}}

==Explanation==

[[Black Hat]] shows his friend [[Cueball]] that he has made a mobile phone application to log and find addresses and business names for the locations of his "friends" using data from {{w|Google Latitude}} which was a location-aware feature of Google Maps that allowed a mobile phone user to allow certain people to view their current location.

The reason it is worth doing so for him, is that most of those that use Google Latitude, haven't learned the habit to turn it off when engaging in "discreet" activities. And then Black Hat can access their whereabout which he then uses in his app.

The second panel shows the screen of Black Hat's smartphone with the logs for his two friend in table form showing activity for [[Megan]] and Robert, the latter log is partially cut off. (Regarding the use of these names see the [[#Trivia|trivia section]]).

Robert's log is fairly innocuous: home at 12:30 PM, school at 2:00 PM and in a {{w|Subway (restaurant)|Subway restaurant}} at 3:30 PM. This log shows that Robert did nothing interesting for Black Hat. There are also several holes in the table compared to the other column. This could either indicate that he stayed this long time those three places, but it could also indicate that Robert has already learned to switch off Latitude when he is not actively using it. This would fit with Black Hat's comment about a narrow window in which people haven't learned this. His friend Robert (which could be the Cueball shown here, see the [[#Trivia|trivia section]]), may already have thought of this himself, or maybe Black Hat has mentioned it to him before getting the idea for the app thus warning him about the problem (without meaning to).

The reason Black Hat states that there only is a ''narrow window of time that people forget to turn Google Latitude off'', is because people like him will make other people, who forgets this, miserable. And then everyone will soon learn to turn the feature off making Black Hat's app useless.

Megan's log appears to prove Black Hat's point: She was home at 11:00 AM, at a {{w|sex toy}} store at 12:30 PM, home again at 1:30 PM, at another sex toy store at 2:00 PM, home again at 2:30 PM, then at {{w|Fry's Electronics}} at 3:00 PM, and directly at a {{w|power tool}} store at 3:30 PM, finally home again at 4:00 PM only to be at the hospital burn ward at 4:10 PM. The last entry is the only one where the interval is not half an hour indicating how fast Megan had to get to the hospital after getting home with her new power tools and electronics (note that Fry is a name, as in Charles Fry, so this was not why she was fried...)

This suggests that Megan first tried the sex toy(s) from the first store, found them insufficiently satisfying, purchased additional sex toys from another store, was still unsatisfied, and then purchased some electronic devices and power tools (either to improve the performance of her sex toys or to apply directly for additional stimulation). The results were apparently more painful than pleasurable, necessitating a quick visit to the hospital burn ward. Overall, Megan has had an at first unsatisfying day and then finally a rather bad day, considering where the burn is most likely to be... She would almost certainly not be pleased to learn that Black Hat has been tracking her whereabouts and sharing this with their mutual friend Cueball.

The title text shows that [[Randall]] liked the T-Mobile G1, also known as the {{w|HTC Dream}}, especially with the new Android upgrade, more than he previously thought because it allows for more capabilities and the interface is clean and easy-to-use when compared to other "smartphones" of that time period (because the G1 was the first phone to introduce {{w|Android}}) and it allows for special Google networking, allowing for apps like Maps to run better (making it easier to run apps like Latitude). From what able to be gathered in the comic, it is [[Black Hat]] who says this, because he is the one who uses the app and shows it off to [[Randall]]. He would be the most likely one to benefit from this kind of phone running this kind of OS/app.

==Transcript==
:[Black Hat is holding a phone up to Cueball.]
:Black Hat: We're in a narrow window in which people are using Google Latitude, but haven't learned the habit of turning it off when they're doing something discreetly.
:Black Hat: I wrote an app to log friends' locations and work out addresses and business names.

:[A timetable is visible. The first column gives the time and splits the day in the half hour intervals starting at 11:00 AM, except for the last entry at 4:10 PM, where the time only jumps 10 minutes. The next two columns represents two persons activities during this time period. In the second column the last letter shown in the comic is partly cut off more or less. This last partly shown letter is written in the transcript, but no guess is made here. See the explanation. Above the table, over the two names, there is a caption:]
:::::<big>Locations</big>
:{| class="wikitable"
|-
|Time ||Megan ||Rober
|-
|11:00 AM || Home ||
|-
|12:30 PM || Eastview Adult Toy Store || Home
|-
|1:30 PM || Home ||
|-
|2:00 PM || Laketown Sex Toy Shop || Schoo
|-
|2:30 PM ||Home ||
|-
|3:00 PM || Fry's Electronics ||
|-
|3:30 PM || Ed's Power Tool Emporium || Subwa
|-
|4:00 PM || Home ||
|-
|4:10 PM || Hospital Burn Ward ||
|}

==Trivia==
*This is one of the handful of times that the name ''Megan'' has been used in xkcd, in this case without actually showing Megan, so there is actually no indication in this comic how she looks. But that has been shown in several others.
**Despite her not being shown, the comic should be listed as featuring Megan, as her name is used.
*Given that Black Hat has sometimes interacted with the Cueball called [[Rob]], it seems likely that the Cueball in this comic is actually Rob (for Robert), and it turns out that he has either forgotten to turn of his Google Latitude, or only has it turned on when he actually uses it. He has in either case only used it in inconspicuous places, and would not be alarmed at seeing the table of his own activities.
**Maybe this is why Black Hat shows it to him, so he can share Megan's event log which is much more interesting.
**That Rob has been at a school could mean he was a teacher or for some other reason needed to go there. It is such a short time span in the afternoon that it does not seem like something a school kid would do.
***Some have, using the school as argument, suggested that this Robert is actually [[Little Bobby Tables]].
***But Black Hat has never interacted with the [[Mrs. Roberts|Roberts family]] so this seems unlikely, and he has never been called Robert, but he has been drawn like a kid looking like Cueball.
**Given that it is unclear if it is either Rob or Bobby neither should be credited as part of this comic.

{{comic discussion}}

[[Category:Comics featuring Cueball]]
[[Category:Comics featuring Black Hat]]
[[Category:Comics featuring Megan]]
[[Category:Comics featuring Rob]]
[[Category:Smartphones]]
[[Category:Charts]]
[[Category:Sex]]

Talk:1779: 2017

2017-02-06T21:16:36Z

172.68.54.64:

Well, we're ending the year off with an optimistic XKCD comic. Here's to another year!
[[User:GranadalandDreamer|GranadalandDreamer]] ([[User talk:GranadalandDreamer|talk]]) 23:07, 30 December 2016 (UTC)

What is five thirty eight? From the context I get it's most likely a TV-Show, but I believe some background information would help here. --[[Special:Contributions/162.158.92.46|162.158.92.46]] 07:14, 31 December 2016 (UTC)
:It's a website. You can click on the link to get more information about it as it links to FiveThirtyEight's Wikipedia article. --[[Special:Contributions/162.158.75.160|162.158.75.160]] 10:00, 31 December 2016 (UTC)

Title text also can be reference to Seveneves by Neal Stephenson. [[User:Magras|Magras]] ([[User talk:Magras|talk]]) 15:52, 31 December 2016 (UTC)

Is there some significance to the fallen tree that they are walking over? Or is it just a visual aid to give them something to do? {{unsigned ip|162.158.74.87}}

Note: in the Russian language words "prime (number)" and "easy" can in be translated to the same word "простой". [[Special:Contributions/141.101.107.168|141.101.107.168]] 07:39, 2 January 2017 (UTC)

"
This is the first odd-numbered years (and thus of course the first prime year)[...] "
I know xkcd didn't exist in the year 2 but the "thus of course the first prime year" still makes me uncomfortable
[[Special:Contributions/198.41.230.100|198.41.230.100]] 09:10, 7 January 2017 (UTC)

Hmmm ... wouldn't vanishing of Moon be problem itself? Disappearance of tides might cause all sorts of climatic problems ... -- [[User:Hkmaly|Hkmaly]] ([[User talk:Hkmaly|talk]]) 06:51, 9 January 2017 (UTC)

For the record, 1933 ([https://en.wikipedia.org/wiki/Adolf_Hitler's_rise_to_power]) was also prime, and also contained a solar eclipse. The eclipse seems to have not passed over Germany though -- so maybe this year won't turn out as bad for Trumpland as that one did for Germany. [[Special:Contributions/172.68.54.64|172.68.54.64]] 21:16, 6 February 2017 (UTC)