explain xkcd - User contributions [en]

2011: Newton's Trajectories

2018-06-25T10:44:31Z

141.101.69.9: /* Explanation */

{{comic
| number = 2011
| date = June 25, 2018
| title = Newton's Trajectories
| image = newtons_trajectories.png
| titletext = With just one extra line, he could have anticipated the 2003 film The Core, but some things are too audacious for even the greatest visionaries.
}}

==Explanation==
{{incomplete|Created by a cannonball - Please change this comment when editing this page. Do NOT delete this tag too soon.}}
The comic shows the Earth, with three apparent spaceships on separate trajectories. One set is released with sufficient velocity to remain in a stable orbit, while the other two fall towards the Earth. This is a slight modification of {{w|Newton's cannonball}}, a thought experiment demonstrating the planetary effects of gravity.

[[File:1669780A-D3EE-43E7-BD94-DD34B224BFF4.gif]]

Here, Newton's cannonball is used both to observe humanity’s technological future (interstellar travel, availability of advanced technology to the masses, and constant scientific improvement, or nuclear desolation and the extinction of our species) and to underscore that argument by pointing out the inherent metaphor in the experiment: the cannonball can only escape the atmosphere by achieving high velocity (i.e. escape velocity). Similarly, technological progress will only deliver us from nuclear extinction if it happens quickly; otherwise, mankind will destroy itself.

The phrase "slip the bonds of Earth" comes from the sonnet "[http://www.arlingtoncemetery.net/highflig.htm High Flight]" written in 1941 by John Gillespie Magee Jr., an American pilot in the Second World War. Portions of this poem appear on the headstones of many interred in Arlington National Cemetery, particularly aviators and astronauts.

The title text alludes to the unfortunate film ''{{w|The Core}}'', involving, obviously, drilling to the center of the Earth. Apparently not even Newton could predict such a disaster.

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

{{comic discussion}}

Talk:1882: Color Models

2017-08-28T21:18:27Z

141.101.69.9:

For those who want to know a bit more about color, [https://www.handprint.com/LS/CVS/color.html this site] is a good start. [[User:Zmatt|Zmatt]] ([[User talk:Zmatt|talk]]) 15:08, 28 August 2017 (UTC)

This comic shows the trend of having a simple and satisfactory explanation for something, and the exasperation with repeatedly realizing the inadequacy of the explanation, making revisions, and having a more complex yet still inadequate model.

As Randall began his schooling, he learned that mixing the primary colours of pigment (red, blue, and yellow) together he could create almost any colour, so colour must be a combination of those 3 colours.

He also learned about rainbows, and that the colours in the rainbow were just different wavelengths of light. Somehow these different wavelengths created unique colours.

As Randall got older, philosophy and a discussion on perception came into play, and Randall came to the realization that his experiences are analogous to but not necessarily the same as his peers.

As he got older, Randall learned about colour spaces as used in pigments, light, and printing, possibly from computer science (Red, Green, Blue; Red, Yellow, Blue; Cyan, Magenta, Yellow, Key) as well as the physics of electromagnetic rays and the biology of vision, understanding that visible light is a small portion of the electromagnetic spectrum - one crudely interpreted by the 3 types of cones in our eyeballs.

Randall then learned about the opponent process model, wherein the signal from cones are not interpreted individually, but in difference to one another. "Responses to one color of an opponent channel are antagonistic to those to the other color. That is, opposite opponent colors are never perceived together – there is no "greenish red" or "yellowish blue"." (from wikipedia)

After that, Randall comes to understand the modeling of colour spaces and the design and limits of human visual perception - despite only having three cones, color space cannot be made into a triangle and still cover the gamut of human colour experience.

Klein manifolds are beyond me, you'll have to fill in something about that.

Eventually, the modeling becomes so complex (and yet still unsatisfactory) that Randall hopes it becomes someone else's problem. [[Special:Contributions/108.162.238.5|108.162.238.5]] 15:50, 28 August 2017 (UTC)MagnusVortex

I'm familiar with klein manifolds, they're peculiar 4D dimensional topological objects related to mobius strips. I have no Idea how they might relate to color, and doing a search for "a hyperdimensional four-sided quantum Klein manifold" returned pictures of bicycles...

It might be good to point out in the explaination that he progresses from a dual nature of color (light, and paint) at the beginning and then trends to a unified explaination of color. [[Special:Contributions/172.68.142.179|172.68.142.179]] 18:27, 28 August 2017 (UTC) Sam

: Yes those are great looking bikes and are called Klein Quantum racing bikes... so Google did its job of keyword matching. [[User:Rtanenbaum|Rtanenbaum]] ([[User talk:Rtanenbaum|talk]]) 20:40, 28 August 2017 (UTC)

;The beauty of explainxkcd
The explanation of this comment is a great example of why this site is delightful — and nigh-invaluable! Thanks, regulars, for doing the work to help us understand all this.{{unsigned ip|108.162.246.101}}

----

Text explanation

I think the explanation of the text is missing an important point. It starts like it's about the philosophal question of "the same color for everybody", but ends with a very mundane explanation, which I think quite funny.

[[Special:Contributions/141.101.69.9|141.101.69.9]] 21:18, 28 August 2017 (UTC) Loïc

1878: Earth Orbital Diagram

2017-08-18T16:48:07Z

141.101.69.9: /* Explanation */

{{comic
| number = 1878
| date = August 18, 2017
| title = Earth Orbital Diagram
| image = earth_orbital_diagram.png
| titletext = You shouldn't look directly at a partial eclipse because of the damage that can be caused by improperly aligning the solar-lunar orbital plane with the orbital bones around your eye.
}}

==Explanation==
{{incomplete|Created by a BOT - Please change this comment when editing this page. Do NOT delete this tag too soon.}}
This comic is the third consecutive comic published in the week before the {{w|solar eclipse}} occurring on Monday, {{w|Solar eclipse of August 21, 2017|August 21, 2017}} which is a total solar eclipse and visible in totality within a band across the {{w|contiguous United States}} from west to east. The other comics are [[1876: Eclipse Searches]] and [[1877: Eclipse Science]].

The comic claims that the reason that eclipses don't happen every month is simple to understand by looking at an orbital diagram. Ironically, the cartoon has so many parts and labels which make it far more difficult to understand than is implied. While the graph itself is based {{w|Orbital elements|astronomical definitions}} all the labels are nonsense in this context.

All these labels are complicated words, some are somewhat related to orbital mechanics ("equinox", "perihelion") while some are just latin sounding nouns. Moreover, many of the labels provided are kludged, obfuscated, or simply made up. Compare/contrast with the standard {{w|Kepler orbit|Kepler Orbit}} diagram. Most easily recognizable are the "Dimples of Venus," referring to axis-intersection points in the diagram on Earth.

The title text refers to 'orbit' being also the anatomical term for the eyesocket.

{| class=wikitable
! Word used in the comics
! Meaning of word used
! Actual astronomical term
! Meaning of actual term

|-
| {{w|Arctangent}}
| The inverse function of the tangent function of trigonometry. You can determine a non-right angle of a right triangle by taking the arctangent of the length of the opposite side divided by the length of the adjacent side.
|
|

|-
| {{w|Astral plane}}
| A plane of existence in various esoteric theories. Also used in fictional fantasy context.
| {{w|Orbit_of_the_Moon|Lunar orbital plane}}
| The plane in which the Moon orbits the Earth that is tilted about 5.1 degrees from the Earth

|-
| {{w|Declension}}
| Inflection of nouns in a language.
| {{w|Inclination}}
| The "tilt" of an orbit

|-
| {{w|Dimples of Venus}}
| Indentations sometimes visible on the human lower back
| {{w|Belt of Venus}}
| Shadow cast by the Earth visible in its atmosphere

|-
| {{w|Enceliopsis}}
| Small genus of flowering plants in the daisy family, appropriately known as "sunrays"
| Ecliptic
| The plane in which the Sun appears to orbit around the Earth - and, accordingly, the plane in which the Earth orbits around the Sun

|-
| {{w|Equinox}}
| Equinox is the point in the year where the length of day and night are roughly equal that is the first day of spring and the first day of autumn. This is due to the rotation axis of the Earth (tilted at 23.5 degrees) is midway between pointing towards or away from the Sun.
|
|

|-
| {{w|Hypothecate}}
| A legal verb that means something similar to "make a mortgage"
|
|

|-
| {{w|Obsequity}}
| The state of being obsequious (showing a willingness to obey or serve)
| {{w|Obliquity}}
| Axial Tilt

|-
| Perihelix
| Portmanteau of helix and perihelion
| {{w|Perihelion}}
| Point in a solar orbit where the body is closest to the Sun

|-
| {{w|Prolapse}}
| A medical condition where an internal organ to move out of place
|
|

|-
| {{w|Sagittal plane}}
| Anatomical plane, dividing the body in left and right; also similar to Sagittarius, a constellation in the Zodiac.
| {{w|Ecliptic plane}}
| The plane in of the Earth's orbit about the Sun

|-
| {{w|Solar plexus}}
| Network of nerves located in the abdomen.
| {{w|Sun}}
| Star in our solar system.

|-
| {{w|Solstice}}
| Solstice is the point in the year where the length of day or night is longest (depending on which hemisphere), due to the 23.5 degree axial tilt of the Earth's rotation pointing directly towards/away from the Sun. This marks the first day of summer and winter.
|
|

|-
| {{w|Tropopause}}
| The boundary in our atmosphere between the troposphere and stratosphere. It is defined as the boundary where air ceases to cool with increasing elevation.
|
|
|}

==Explanation for "Why isn't there a (solar) eclipse every month?"==

If the plane of where the Earth orbits the Sun and where the Moon orbits the Earth were completely aligned, then there would be a solar eclipse at every New Moon (once every [https://en.wikipedia.org/wiki/Orbit_of_the_Moon#Lunar_periods 29.5 days]) and a lunar eclipse at every full moon (half a lunar period about 14.7 days after a New Moon). However, the plane in which the Moon orbits the Earth is tilted with an inclination of 5 degrees relative to that of the ecliptic plane (the plane defined by the Earth's orbit around the Sun). Eclipses are only possible during two eclipse seasons each year (half a year apart) where for a period of 31 to 37 days the Sun is nearly aligned with the two points in the tilted Earth-Moon plane where the Moon crosses the ecliptic plane. During an eclipse season at the time of a new moon there will be solar eclipses visible from certain locations and during full moons there will be lunar eclipses.

[[Image:Eclipse_Diagram.jpg]]

The real explanation of eclipses is evident from this xkcd comic, but is labeled with a fictional character similar to a Greek Phi but with two vertical lines; the remaining labels also do not contribute to this explanation and exist only to distract or misinform the reader.

==Transcript==
{{incomplete transcript|Do NOT delete this tag too soon.}}
:[An orbital map of the Earth is shown. The Sun is in the center, the Earth is at the right bottom, and the Moon is left below the Earth.]
:'''Why isn't there an eclipse every month?'''
:This is a common question! The answer is made clear by a quick look at the Earth's orbital diagram:

:[Label Sun:]
:Solar plexus

:[Label on the Earth's plane:]
:Sagittal plane

:[Labels on Earth's orbit (beginning at the Earth counterclockwise):]
:Perihelix, Declension, Obsequity, Hypothecate, Enceliopsis, Equinox (''Solstice'' in British English)

:[Two angles in the plane are labeled as:]
:Determinant of the date of Easter, Arctangent

:[The plane of the Moon is pictured in a small angle to the Earth's plane and named Astral Plane. The angel is presented between two lines (Greek Nu or Gamma and a double Greek Chi) and identified by a character that looks similar to a Greek Phi but with two vertical lines.]
:[The labels at the Moon's path are:]
:Tropopause, Prolapse, Errata.

:[An arrow points to the Earth at the zero meridian on the equator. The label reads:]
:Dimples of Venus

{{comic discussion}}

[[Category:Astronomy]]