# ­xkcd thread **URL:** \ **Category:** Cafe Society\ **Tags:** comic-strips\ **Created:** [May 28, 2020, 12:57am UTC](https://boards.straightdope.com/t/xkcd-thread/854574 "2020-05-28T00:57:03Z")\ **Posts on this page:** 20\ **Page:** 289
**Author:** ![Cheesesteak](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cheesesteak/32/3694_2.png) [@Cheesesteak](https://boards.straightdope.com/u/Cheesesteak)\ **Post date:** [April 15, 2026, 8:28pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/5763 "2026-04-15T20:28:13Z")
> [@TroutMan](#): > > So why is air the one thing we describe differently? Air isn’t blue, the sky is blue. Air is colorless. From an airplane, you can look through 200 miles of air and it doesn’t make everything below it blue or red or anything. From the ground, you look through 60 miles of air and it’s blue. From a space ship, you look through 60 miles of air and it’s clear. ---
**Author:** ![DesertDog](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/desertdog/32/11503_2.png) [@DesertDog](https://boards.straightdope.com/u/DesertDog)\ **Post date:** [April 15, 2026, 8:30pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/5764 "2026-04-15T20:30:55Z")
While I wasn’t paying the strictest attention _all_ of the time, I don’t recall anything being stated in anything but seconds. For example the burn at perigee that kicked Integrity all the way out to the moon was described as a 17-second burn. ---
**Author:** ![Tamerlane](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tamerlane/32/7602_2.png) [@Tamerlane](https://boards.straightdope.com/u/Tamerlane)\ **Post date:** [April 15, 2026, 8:31pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/5765 "2026-04-15T20:31:53Z")
> [@TroutMan](#): > > But we don’t say a rose is colorless and it’s only reflection that makes it look red. Because for better or worse people seem to be interested in the distinction between structural color and pigment. [Green birds is one of the classics](https://daily.jstor.org/green-birds-arent-really-green/). You’ll see that article insist that in fact only one green bird exists or is ‘truly green.’ They get that wrong in the sense it is one small order of birds - there are a number of species in the group with green pigment. But people do like to make that distinction, logical or not. So, [green bird](https://upload.wikimedia.org/wikipedia/commons/9/90/Tauraco_persa_-captive-8a.jpg). [Not-a-green-bird](https://cdn.download.ams.birds.cornell.edu/api/v2/asset/644009012/1200) 😀. Which to most sane people actually is a green bird. ---
**Author:** ![Pardel-Lux](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/pardel-lux/32/20182_2.png) [@Pardel-Lux](https://boards.straightdope.com/u/Pardel-Lux)\ **Post date:** [April 15, 2026, 8:43pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/5766 "2026-04-15T20:43:09Z")
> [@Tamerlane](#): > > They get that wrong in the sense I love your nitpick and your pictures. Very well put. 🙂 ---
**Author:** ![TroutMan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/troutman/32/6721_2.png) [@TroutMan](https://boards.straightdope.com/u/TroutMan)\ **Post date:** [April 15, 2026, 8:48pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/5767 "2026-04-15T20:48:56Z")
> [@Cheesesteak](#): > > Air isn’t blue, the sky is blue. What is scattering the light? Air, or the sky? ---
**Author:** ![Pardel-Lux](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/pardel-lux/32/20182_2.png) [@Pardel-Lux](https://boards.straightdope.com/u/Pardel-Lux)\ **Post date:** [April 15, 2026, 9:06pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/5768 "2026-04-15T21:06:26Z")
The sky is made of air, right? So, same difference. ---
**Author:** ![SunUp](https://avatars.discourse-cdn.com/v4/letter/s/ea5d25/32.png) [@SunUp](https://boards.straightdope.com/u/SunUp)\ **Post date:** [April 15, 2026, 9:08pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/5769 "2026-04-15T21:08:59Z")
The air scattering the light is what makes the sky blue. Air is concrete - it’s a mix of nitrogen, oxygen, carbon dioxide, water vapor and various other gases. The sky is an abstraction - it is what we see that is bounded by the horizon when we are not looking at the ground. Of course, we should say that the clear sky is blue during the day, as the non-clear day sky is the color of clouds, and the clear night sky is black, and in sunsets… you get the picture. ---
**Author:** ![Pleonast](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/pleonast/32/1183_2.png) [@Pleonast](https://boards.straightdope.com/u/Pleonast)\ **Post date:** [April 16, 2026, 12:11am UTC](https://boards.straightdope.com/t/xkcd-thread/854574/5770 "2026-04-16T00:11:02Z")
> [@Cheesesteak](#): > > Air is colorless. From an airplane, you can look through 200 miles of air and it doesn’t make everything below it blue or red or anything. From the ground, you look through 60 miles of air and it’s blue. From a space ship, you look through 60 miles of air and it’s clear. From a mountaintop, looking out to other mountaintops, the more distant mountaintops are definitely more blue. This is very noticeable when all the mountaintops are covered with white snow. Is it because the snow is reflecting the blue sky, or because of the inbetween air? The color of snow is one of those weird ones we call “white”, even though that’s due to its physical structure and not pigment. Unless it’s yellow; that’s definitely a pigment. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [April 16, 2026, 12:16am UTC](https://boards.straightdope.com/t/xkcd-thread/854574/5771 "2026-04-16T00:16:33Z")
> **[Make It Myself](https://xkcd.com/3233/)** [![](https://imgs.xkcd.com/comics/make_it_myself.png) ](https://imgs.xkcd.com/comics/make_it_myself.png) > [@](#): > > “It's not as big a loss as it looks, because now I have have leftover supplies, which will help me talk myself into doing this all over again with a new project!” ---
**Author:** ![Pleonast](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/pleonast/32/1183_2.png) [@Pleonast](https://boards.straightdope.com/u/Pleonast)\ **Post date:** [April 16, 2026, 12:20am UTC](https://boards.straightdope.com/t/xkcd-thread/854574/5772 "2026-04-16T00:20:15Z")
Plus the added entertainment value my friends get when they watch me do it. Oh, and then their entertainment from me explaining this all to my spouse. ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [April 16, 2026, 12:37am UTC](https://boards.straightdope.com/t/xkcd-thread/854574/5773 "2026-04-16T00:37:13Z")
Snow has a very distinct purplish cast. Uncontaminated glacial ice is very much bright blue. Whatever color snow and Ice are, it isn’t white. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [April 16, 2026, 1:31am UTC](https://boards.straightdope.com/t/xkcd-thread/854574/5774 "2026-04-16T01:31:50Z")
Glacial ice is bright blue precisely because it’s contaminated. It contains fine rock powder that provides structural color, similar to blue bird feathers. ---
**Author:** ![Lumpy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lumpy/32/446_2.png) [@Lumpy](https://boards.straightdope.com/u/Lumpy)\ **Post date:** [April 16, 2026, 1:40am UTC](https://boards.straightdope.com/t/xkcd-thread/854574/5775 "2026-04-16T01:40:53Z")
Heh, I’m reminded of all the YouTube videos about salvaging spare components out of various things– usually by adding lots of hardware and using a small machine shop’s worth of tools. I mean, technically yes you can use the graphite rod out of the center of a AA battery as part of a homemade soldering iron but what’s the point? ---
**Author:** ![DPRK](https://avatars.discourse-cdn.com/v4/letter/d/4491bb/32.png) [@DPRK](https://boards.straightdope.com/u/DPRK)\ **Post date:** [April 16, 2026, 3:15am UTC](https://boards.straightdope.com/t/xkcd-thread/854574/5776 "2026-04-16T03:15:41Z")
> [@DesertDog](#): > > While I wasn’t paying the strictest attention _all_ of the time, I don’t recall anything being stated in anything but seconds. For example the burn at perigee that kicked Integrity all the way out to the moon was described as a 17-second burn. Is the audio/transcripts of the audio available? Because they absolutely were stating delta-V’s over the radio [but they said stuff like “nine point five”, units were not explicitly named?]. And angles… just the burn time by itself is not enough to specify the burn impulse. ---
**Author:** ![DesertDog](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/desertdog/32/11503_2.png) [@DesertDog](https://boards.straightdope.com/u/DesertDog)\ **Post date:** [April 16, 2026, 5:08am UTC](https://boards.straightdope.com/t/xkcd-thread/854574/5777 "2026-04-16T05:08:21Z")
I just figured they ran the engine at max impulse. ---
**Author:** ![DPRK](https://avatars.discourse-cdn.com/v4/letter/d/4491bb/32.png) [@DPRK](https://boards.straightdope.com/u/DPRK)\ **Post date:** [April 16, 2026, 5:24am UTC](https://boards.straightdope.com/t/xkcd-thread/854574/5778 "2026-04-16T05:24:20Z")
Indeed, I am not sure those manoeuvring thrusters are throttleable, but I am talking about the delta-V numbers they read out during the preparation for each burn. (Those would be in some units of velocity, by the way, not impulse). It stands to reason that the same units are used by the flight computer, too— unless there is some unit conversion happening? ---
**Author:** ![Pardel-Lux](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/pardel-lux/32/20182_2.png) [@Pardel-Lux](https://boards.straightdope.com/u/Pardel-Lux)\ **Post date:** [April 16, 2026, 7:19am UTC](https://boards.straightdope.com/t/xkcd-thread/854574/5779 "2026-04-16T07:19:21Z")
> [@Lumpy](#): > > but what’s the point? The point, obviously, is to make YouTube videos hoping they become viral. ☝ ---
**Author:** ![DPRK](https://avatars.discourse-cdn.com/v4/letter/d/4491bb/32.png) [@DPRK](https://boards.straightdope.com/u/DPRK)\ **Post date:** [April 16, 2026, 7:53am UTC](https://boards.straightdope.com/t/xkcd-thread/854574/5780 "2026-04-16T07:53:29Z")
Here is an example: the trajectory correction burn on April 5/6. They were given a Delta-V of 10.4, and a burn time of 19 seconds, attitude such-and-such, delta-V _x_, _y_, and _z_ of 4.7, −5.3, 7.6. That has to be feet per second to match the recorded velocity change, which was about 3 m/s. They were lucky not to get launched into the Sun, or otherwise meet the fate of that Climate Orbiter… ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [April 16, 2026, 10:43am UTC](https://boards.straightdope.com/t/xkcd-thread/854574/5781 "2026-04-16T10:43:15Z")
> [@Lumpy](#): > > Heh, I’m reminded of all the YouTube videos about salvaging spare components out of various things– usually by adding lots of hardware and using a small machine shop’s worth of tools. I mean, technically yes you can use the graphite rod out of the center of a AA battery as part of a homemade soldering iron but what’s the point? Or designs for a “3d printed 3d printer”. Which usually call for cannibalizing most of the parts from an existing 3d printer, because most of the parts for a 3d printer can’t be printed. ---
**Author:** ![Q.Q.Switcheroo](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/q.q.switcheroo/32/5713_2.png) [@Q.Q.Switcheroo](https://boards.straightdope.com/u/Q.Q.Switcheroo)\ **Post date:** [April 16, 2026, 4:11pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/5782 "2026-04-16T16:11:42Z")
Ron Swanson: > It’s not rocket science. I removed the sconce… Fired up my grandfather’s torch, heated up the pieces in a cast-iron bucket. Liquefied the metal. Pour it into a mold. Obviously keep it over a low flame to achieve a nice temper. Cooled it in antifreeze. And just forged and shaped the rings. Any moron with a crucible, an acetylene torch, and a cast-iron waffle maker could have done the same. Whole thing only took me about 20 minutes. People who buy things are suckers. [Previous page](https://boards.straightdope.com/t/xkcd-thread/854574.md?page=288) [Next page](https://boards.straightdope.com/t/xkcd-thread/854574.md?page=290)