explain xkcd - User contributions [en]

Talk:2087: Rocket Launch

2018-12-20T03:20:19Z

Tyanderson91:

I had to fight the urge to type Care Bare [[User:Arachrah|Arachrah]] ([[User talk:Arachrah|talk]])

This was published during the Arianespace launch livestream, between launch and satellite deployment: https://www.youtube.com/watch?v=mpHJoo0h8GQ [[User:Fabian42|Fabian42]] ([[User talk:Fabian42|talk]]) 17:11, 19 December 2018 (UTC)

Looks like it could be an Ariane5 in the comic, it is a 3 stage. Anyone know if Max-CB is a real thing (and before I get any wisecracks, I know there aren't any Care Bears in the clouds) [[Special:Contributions/162.158.63.214|162.158.63.214]] 20:27, 19 December 2018 (UTC)

: A search for rocketry terminology reveals that Cb stands for Ballistic Coefficient, which is a measure of the ability to coast. It is related to both velocity and air density, which vary throughout a rocket launch, so it makes sense that there might be some point of maximum ballistic coefficient. (Note: I am not a rocket scientist, and this is clearly rocket science, so take this with a grain of salt!) [[User:Ianrbibtitlht|Ianrbibtitlht]] ([[User talk:Ianrbibtitlht|talk]]) 21:13, 19 December 2018 (UTC)

: Pontificating further, it is reasonable to conjecture that as a rocket accelerates to higher speeds, the drag from the atmosphere increases with increasing speed, but past a certain point the drag begins to decrease as the air gets thinner. This suggests there is some point somewhere during the launch sequence where aerodynamic drag reaches a maximum value - aka Max Cb. [[User:Ianrbibtitlht|Ianrbibtitlht]] ([[User talk:Ianrbibtitlht|talk]]) 21:26, 19 December 2018 (UTC)

: Finally one I can help with! Okay, I don't think this is ballistic coefficient for several reasons: 1. Ballistic Coefficient is typically noted by the greek letter Beta, not Cb. 2. Ballistic coefficient is mass divided by drag area (drag coefficient times reference area). Basically a shape parameter. So while the mass does change over the course of the flight (burning fuel), the drag area does not. Making this a somewhat useless parameter for a launch vehicle 3. Ballistic Coefficient is typically reported as a static parameter rather than a time-varying parameter, so "Max ballistic coefficient" is a rather unusual metric (and would occur on the launch pad in any case, when mass is highest). Finally, as an aside, objects with high ballistic coefficients tend to fly through the air easily and are not influenced very much by wind (such as rocks or bullets), whereas low-beta objects can by pushed and slowed down a lot by the wind (such as balloons). [[User:Tyanderson91|Tyanderson91]] ([[User talk:Tyanderson91|talk]]) 03:17, 20 December 2018 (UTC)

r/shittyspacexideas --[[Special:Contributions/173.245.52.139|173.245.52.139]] 19:53, 19 December 2018 (UTC)

If you trace the dotted lines, it seems that the Boosters are the winners[[User:CCCVVVA|CCCVVVA]] ([[User talk:CCCVVVA|talk]]) 03:02, 20 December 2018 (UTC)

This was posted on the day SpaceX was supposed to launch the GPS-III-2 satellite, which may be the reason for the mention of GPS [[User:Tyanderson91|Tyanderson91]] ([[User talk:Tyanderson91|talk]])

Talk:2087: Rocket Launch

2018-12-20T03:18:15Z

Tyanderson91:

I had to fight the urge to type Care Bare [[User:Arachrah|Arachrah]] ([[User talk:Arachrah|talk]])

This was published during the Arianespace launch livestream, between launch and satellite deployment: https://www.youtube.com/watch?v=mpHJoo0h8GQ [[User:Fabian42|Fabian42]] ([[User talk:Fabian42|talk]]) 17:11, 19 December 2018 (UTC)

Looks like it could be an Ariane5 in the comic, it is a 3 stage. Anyone know if Max-CB is a real thing (and before I get any wisecracks, I know there aren't any Care Bears in the clouds) [[Special:Contributions/162.158.63.214|162.158.63.214]] 20:27, 19 December 2018 (UTC)

: A search for rocketry terminology reveals that Cb stands for Ballistic Coefficient, which is a measure of the ability to coast. It is related to both velocity and air density, which vary throughout a rocket launch, so it makes sense that there might be some point of maximum ballistic coefficient. (Note: I am not a rocket scientist, and this is clearly rocket science, so take this with a grain of salt!) [[User:Ianrbibtitlht|Ianrbibtitlht]] ([[User talk:Ianrbibtitlht|talk]]) 21:13, 19 December 2018 (UTC)

: Pontificating further, it is reasonable to conjecture that as a rocket accelerates to higher speeds, the drag from the atmosphere increases with increasing speed, but past a certain point the drag begins to decrease as the air gets thinner. This suggests there is some point somewhere during the launch sequence where aerodynamic drag reaches a maximum value - aka Max Cb. [[User:Ianrbibtitlht|Ianrbibtitlht]] ([[User talk:Ianrbibtitlht|talk]]) 21:26, 19 December 2018 (UTC)

: Finally one I can help with! Okay, I don't think this is ballistic coefficient for several reasons: 1. Ballistic Coefficient is typically noted by the greek letter Beta, not Cb. 2. Ballistic coefficient is mass divided by drag area (drag coefficient times reference area). Basically a shape parameter. So while the mass does change over the course of the flight (burning fuel), the drag area does not. Making this a somewhat useless parameter for launch vehicle 4. Ballistic Coefficient is typically reported as a static parameter rather than a time-varying parameter, so "Max ballistic coefficient" is a rather unusual metric (and would occur on the launch pad in any case, when mass is highest). Finally, as an aside, objects with high ballistic coefficients tend to fly through the air easily and are not influenced very much by wind (such as rocks or bullets), whereas low-beta objects can by pushed and slowed down a lot by the wind (such as balloons). [[User:Tyanderson91|Tyanderson91]] ([[User talk:Tyanderson91|talk]]) 03:17, 20 December 2018 (UTC)

r/shittyspacexideas --[[Special:Contributions/173.245.52.139|173.245.52.139]] 19:53, 19 December 2018 (UTC)

If you trace the dotted lines, it seems that the Boosters are the winners[[User:CCCVVVA|CCCVVVA]] ([[User talk:CCCVVVA|talk]]) 03:02, 20 December 2018 (UTC)

This was posted on the day SpaceX was supposed to launch the GPS-III-2 satellite, which may be the reason for the mention of GPS [[User:Tyanderson91|Tyanderson91]] ([[User talk:Tyanderson91|talk]])

Talk:2087: Rocket Launch

2018-12-20T03:17:03Z

Tyanderson91:

I had to fight the urge to type Care Bare [[User:Arachrah|Arachrah]] ([[User talk:Arachrah|talk]])

This was published during the Arianespace launch livestream, between launch and satellite deployment: https://www.youtube.com/watch?v=mpHJoo0h8GQ [[User:Fabian42|Fabian42]] ([[User talk:Fabian42|talk]]) 17:11, 19 December 2018 (UTC)

Looks like it could be an Ariane5 in the comic, it is a 3 stage. Anyone know if Max-CB is a real thing (and before I get any wisecracks, I know there aren't any Care Bears in the clouds) [[Special:Contributions/162.158.63.214|162.158.63.214]] 20:27, 19 December 2018 (UTC)

: A search for rocketry terminology reveals that Cb stands for Ballistic Coefficient, which is a measure of the ability to coast. It is related to both velocity and air density, which vary throughout a rocket launch, so it makes sense that there might be some point of maximum ballistic coefficient. (Note: I am not a rocket scientist, and this is clearly rocket science, so take this with a grain of salt!) [[User:Ianrbibtitlht|Ianrbibtitlht]] ([[User talk:Ianrbibtitlht|talk]]) 21:13, 19 December 2018 (UTC)

: Pontificating further, it is reasonable to conjecture that as a rocket accelerates to higher speeds, the drag from the atmosphere increases with increasing speed, but past a certain point the drag begins to decrease as the air gets thinner. This suggests there is some point somewhere during the launch sequence where aerodynamic drag reaches a maximum value - aka Max Cb. [[User:Ianrbibtitlht|Ianrbibtitlht]] ([[User talk:Ianrbibtitlht|talk]]) 21:26, 19 December 2018 (UTC)

: Finally one I can help with! Okay, I don't think this is ballistic coefficient for several reasons: 1. Ballistic Coefficient is typically noted by the greek letter Beta, not Cb. 2. Ballistic coefficient is mass divided by drag area (drag coefficient times reference area). Basically a shape parameter. So while the mass does change over the course of the flight (burning fuel), the drag area does not. Making this a somewhat useless parameter for launch vehicle 4. Ballistic Coefficient is typically reported as a static parameter rather than a time-varying parameter, so "Max ballistic coefficient" is a rather unusual metric (and would occur on the launch pad in any case, when mass is highest).
As an aside, objects with high ballistic coefficients tend to fly through the air easily and are not influenced very much by wind (such as rocks or bullets), whereas low-beta objects can by pushed and slowed down a lot by the wind (such as balloons). [[User:Tyanderson91|Tyanderson91]] ([[User talk:Tyanderson91|talk]]) 03:17, 20 December 2018 (UTC)

r/shittyspacexideas --[[Special:Contributions/173.245.52.139|173.245.52.139]] 19:53, 19 December 2018 (UTC)

If you trace the dotted lines, it seems that the Boosters are the winners[[User:CCCVVVA|CCCVVVA]] ([[User talk:CCCVVVA|talk]]) 03:02, 20 December 2018 (UTC)

This was posted on the day SpaceX was supposed to launch the GPS-III-2 satellite, which may be the reason for the mention of GPS [[User:Tyanderson91|Tyanderson91]] ([[User talk:Tyanderson91|talk]])

1973: Star Lore

2018-03-28T16:39:04Z

Tyanderson91: Reference to Five Sisters

{{comic
| number = 1973
| date = March 28, 2018
| title = Star Lore
| image = star_lore.png
| titletext = That one is a variable star which pulses every 30 seconds. Its name comes from a Greek word meaning "smoke alarm."
}}

==Explanation==
{{incomplete|Created by a BOT running on a COMPUTER with TOO MANY STATUS LEDs - Please change this comment when editing this page. Do NOT delete this tag too soon.}}

Computers, chargers, and other electronic items often have status lights in various colors. In a dark room, these lights appear as pinpricks of light, similar to constellations. Presumably Randall's room has many such items, though this may be like [[My Hobby]] in the sense that his room doesn't really look like that but he claims it does for humor value. It's also not clear whether this refers to Randall's bedroom (typical US usage of "my room" refers to one's bedroom) or some other room Randall spends a good deal of time in.

The comic's narrator is explaining how some of his lights remind him of stars, which gives him an opportunity to show off his knowledge of astronomic trivia. "The Five Sisters" is a reference to a pentagon-shaped constellation from Issac Asimov's book ''Foundation's Edge'', though it could not have been 'known to the ancients' since it was less than 100 years old.

Interestingly, there are some green stars. Stars might look green due to a neighbouring star, but {{w|Green star (astronomy)|green stars are actually impossible}} due to the principle of black body radiation.

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

:[Assorted dots of various colors scattered around the panel, with two speech bubbles randomly placed in the panel]
:Speech bubble 1: That cluster was known to the ancients as the Five Sisters.
:The red one was a supergiant and will probably explode within the next million years.
:Speech bubble 2: Wow!

:[Caption below the panel:]
:There are too many status LEDs in my room.
{{comic discussion}}

Talk:1973: Star Lore

2018-03-28T16:04:31Z

Tyanderson91:

Doesn't appear that "Five Sisters" is a reference to anything, according to my Google searches. Does anyone have anything on that? [[Special:Contributions/108.162.221.53|108.162.221.53]] 15:13, 28 March 2018 (UTC)Martin
If I had to guess, it's most likely a reference to the Pleiades (Seven Sisters), which is a constellation.[[Special:Contributions/172.68.34.94|172.68.34.94]] 15:18, 28 March 2018 (UTC)

I keep 'cellulose' tape over my LEDs, darkened with permanent marker, to dim their harsh glare when the rooms are unlit. On important ones, I keep a small sliver uncovered, so that from the right angle (like from the doorway) they can be seen even with the lights on. I do wish more devices had a "dim" setting on a timer, so the LEDs could be bright during the day & barely lit at night. In particular, my backup power battery has a large, obnoxious blue screen that lights up the whole room unless I keep it facing the wall. [[User:ProphetZarquon|ProphetZarquon]] ([[User talk:ProphetZarquon|talk]]) 15:48, 28 March 2018 (UTC)

The red LED probably is a super bright LED :-) Sebastian --[[Special:Contributions/162.158.111.37|162.158.111.37]] 16:00, 28 March 2018 (UTC)

"Five Sisters" is a reference a pentagon-shaped constellation from Isaac Asimov's ''Foundations Edge'' ~~Tyler