explain xkcd - User contributions [en]

Talk:2729: Planet Killer Comet Margarita

2023-01-25T21:41:49Z

172.68.70.120: Number of Margaritas produced by Randall's Recipe

A standard LR1 oil tanker holds, at most, [[25.8 million] https://www.eia.gov/todayinenergy/detail.php?id=17991#:~:text=These%20ships%20can%20access%20most,of%20light%20sweet%20crude%20oil.] gallons of gasoline. At an IBA specification of 50ml of tequila per margarita, Randall's ratio would make 1.95 billion margaritas, or around 6 for every resident of the United States assuming they could all be assembled at the base of Lake Mead.

2725: Sunspot Cycle

2023-01-17T15:56:07Z

172.68.70.120: /* Explanation */ copyediting

{{comic
| number = 2725
| date = January 16, 2023
| title = Sunspot Cycle
| image = sunspot_cycle_2x.png
| imagesize = 740x503px
| noexpand = true
| titletext = Who can forget the early 2010s memes? 'You know you're a 90s kid if you remember the feeling of warm sunlight on your face.' 'Only 90s kids remember the dawn.'
}}

==Explanation==
{{incomplete|Created by a NINETIES KID WHO FELT SUN - Please change this comment when editing this page. Do NOT delete this tag too soon.}}

This comic is a reference to the {{w|solar cycle}}, which is a roughly 11-year cycle of changes in the Sun's activity from a period of minimal levels of various related phenomena ({{w|sunspots}}, solar radiation, ejecta, and solar flares) to one of maximum activity in these areas. As the cycle continues, the Sun returns to minimal activity and starts over. Without actually studying the Sun, however, there is no discernable difference to our daily lives here on Earth, and studying the Sun in enough detail is difficult due to its intrinsic and eye-damaging brightness whenever viewed directly.

This comics makes a joke that when the absolute number of sunspots appears to decrease it is not because they disappear, but because they get so crowded that they begin to merge, and thus the number of individual spots decreases whereas the area of the sun covered by sunspots continues to increase to near total 'darkness'. This causes there to be a completely dark Sun after 11 years, at which point any new sunspots are ''bright'' patches, and the next 11-year cycle repeats the process but accumulating bright spots until eventually it is all bright once more, giving a total bright/dark cycle of 22 years.

The curve showing the number of differentiable sunspots in this 22-year cycle would follow the curves for two whole cycles of our normal Sun, as the number of distinct spots (of either kind) decreases down to practically just one Sun-enveloping spot. The change in brightness over the cycle, however, repeats only over the full 22 years, darkening and then being made to shine bright once more as the other type of spot appears and begins to dominate once more.

Below is a graph showing the number of sunspots as a function of time from around 1965 to 2025. Periods where the sun is dark are shown with black under the curve, and in transition periods with lines of darkness getting closer together on the way to 'fully' dark area plus vals of light reinserting themselves in the lightening part of the cycle. Also for clarity the troughs are labeled with the sun being bright or dark. It is always when there are few spots that the sun is either completely free from spots and thus bright, or completely covered and thus dark. The maxima are always one or other extreme, alternating, the transition period starting as the curve rises towards these and ending as it falls away again.

From this curve it can be seen that the Sun was bright in the 1990s, but not in the dark 1980s or the dark time from around 2001 to 2014. This fact is mentioned in the title text (see below). Similarly the 1970s were bright, after dark 1960s. But after the darkness began around 2000 it first got bright again around 2014. Finally darkness starts again around 2024. So the cycles are not perfectly 11 years long and there could be changes during a cycle like the one around 2013-2014 where there is a clear peak in the number of sunspots but darkness prevails. Maybe the large spots split up into several small ones, but staying close to each other, without getting much less area covered. The count would go up if they were no longer merged together, but the brightness might not increase much.

This would obviously be catastrophic if it happened in our version of the universe, as during a dark phase no light would be coming from the Sun, so the Earth would freeze if all wavelengths of the Sun were blocked. If the spots only affect light in the visible spectrum, then Earth would not freeze but plants would have trouble with photosynthesis. In our universe sunspots cool the area of the Sun where they appear but they are not totally dark; [https://image.gsfc.nasa.gov/poetry/workbook/sunspot.html NASA says] that each sunspot on its own would glow orange, brighter than the Moon is when it is full (and the Sun is normally bright, to have illuminated it). So even in a completely sunspot-covered Sun, the Sun would still be brighter than the Moon (ought to be), and it would be possible to see it rise even if the heat delivered were very low. See more in the title text explanation.

These problems are obviously not a serious threat in the reality of the comic, as the Sun is truly dark and people survive these dark periods. This becomes clear in the title text where internet memes indicate that people lived fine through the dark periods, although they obviously did not see the sun as kids if they were born during the early start of the next dark period.

The title text thus indicates the effect on internet memes that the special solar cycle has. During the 2010s in our universe there were many '90s kid' memes. Those were also popular in this universe, but they reflect that the Earth had at that time been dark since the 2000s, and thus only those born in the 1990s and before would remember dawn or the feeling of the warm sun on their faces.

This of course indicates that the Sun is actually dark and gives no warmth. Thus it is a mystery how life on Earth prevails, but given that there were kids from the 1990s that made memes twenty years after, life does work in this strange alternate universe.

==Transcript==
:[This comics shows two graphs, one also with several images of the Sun in different times in the solar cycle. The top graph is much larger than the bottom graph, and above them is a explanation of what the graphs shows:]
:Ever wonder why the sun disappears for about 10 years every other decade? This terrifying period of worldwide darkness is a natural consequence of the 11-year sunspot cycle:

:[A graph is shown with a label above the arrow on the Y-axis and a label written above the left part of the X-axis with an arrow pointing from it to the right (there is not arrow on the X-axis line). The graph shows a sine curve with a dashed line. It starts close to the bottom and then increases, then decreases before i finally slightly increases again. Above the dashed line are eight circles representing the sun with various levels of sunspots, with an arrow between each circle pointing to the next to the right. All circles are just above the dashed curve and the small arrows between them also follow the curvature of the line, so this string makes the same shape as the curve. along the eight representation of the sun there are five labels. The eight Suns will be described below with labels given when relevant.]
:Y-Axis: Sunspot number
:Y-Axis: Time

:[The first Sun's circle is completely white]

:[The second Sun's circle has a few sunspots. A label is written to the left of it:]
:Dark sunspots appear

:[The third Sun's circle has several sunspots. A label is written to the left of it:]
:Sunspot number rises

:[The fourth Sun's circle is half covered in sunspots.]

:[The fifth Sun's circle is mostly black with a few lines of white dots. Between the fourth and fifth circle is a label:]
:Number falls as sunspots merge.

:[The sixth Sun's circle is almost completely black with just a few small white spots. A label is written above it:]
:Sunspots envelop sun, Earth enters years of darkness.

:[The seventh Sun's circle is mostly black with a few light areas.]

:[The eighth Sun's circle is still mostly black but with some larger white areas. A label is written above and left of it:]
:Bright sunspots appear, cycle reverses.

:[Below is a second graph with a label written near the top of the Y-axis which is otherwise not labeled. The X-axis also has no label, but six years are written beneath at equal intervals. The graph shows a similar sine curve as the one above, but with almost five cycles shown. Also each cycle is not close to being a perfect sine curve, but has the property with a peak followed by a trough. The five troughs are labeled. The area beneath the curve alternates from being black and white when there is a trough, with the peak in between having several vertical lines, indicating transfer from black to white and vise versa. There are not same distance between peaks and there are also features on the graphs, for instance the two peaks in the middle has a drop, so they look like volcanoes. And the last full peak has a clear outlier year with many sunspots.]
:Label: History:
:X-axis labels: 1970 1980 1990 2000 2010 2020
:Through 1970-1980: Sun is bright
:Through 1980-1990: Sun is dark
:Through 1990-2000: Sun is bright
:Through 2000-2010: Sun is dark
:Through 2010-2020: Sun is bright

{{comic discussion}}

[[Category:Astronomy]]
[[Category:Timelines]]
[[Category:Line graphs]]
[[Category:Internet]]

2058: Rock Wall

2022-11-25T17:42:23Z

172.68.70.120: launch has been rescheduled

{{comic
| number = 2058
| date = October 12, 2018
| title = Rock Wall
| image = rock_wall.png
| titletext = I don't trust mantle/core geologists because I suspect that, if they ever get a chance to peel away the Earth's crust, they'll do it in a heartbeat.
}}

==Explanation==
{{w|Mantle_(geology)|Mantle}} {{w|geologists}} study that {{w|Structure_of_the_Earth|part of the planet}} that's below the top "{{w|Crust_(geology)|crust}}" of the planet. The top layer of the planet, which is several dozen miles thick, is the only layer we've been able to explore, by {{w|mining|digging tunnels}}, {{w|spelunking}}, etc. The only way to study the mantle and other inner layers of the earth are through non-visual, non-tactile, indirect methods, and by analyzing old samples of the mantle that have made their way to the surface.

In this comic, [[Ponytail]], talking to [[Megan]], is describing her job as a mantle geologist as that of living on one side of a thick wall that is, and likely always will be, impossible to get around, but she has to study what is on the other side of the wall. In this case the wall is horizontal rather than vertical, the wall being the earth's crust, and makes a complete sphere, so the only way to get past the wall would be to go through. It is theoretically possible to go through, but as of the comic's posting, humanity is far from doing so. (The deepest hole dug as of at that time, as measured by {{w|true vertical depth}}, is the {{w|Kola_Superdeep_Borehole|Kola Borehole}}, which only goes down to 12,262 meters out of the estimated 35,000 meters needed to get through at that location.)

In the title text [[Randall]] states that he doesn't trust mantle/core geologists. Because if they got the chance he believes they would not hesitate (even the duration of a heartbeat) to strip away Earth's crust to study the mantle or even worse the {{w|Inner core|core}} directly. Of course if they only did this locally to look at the mantle it would not shatter the Earth although that local area may become a volcano. But if they actually peeled the entire outer layer away, we humans would have no place to live, as the mantle is really hot and would melt easily (producing magmas and therefore lavas when magma’s exposed to surface, see title text of [[1405: Meteor]] to be more confused). However, after a while all these erupted lavas would solidify and become a new crust. Humanity needs to withstand just some millennia of active worldwide volcanism.

If they somehow exposed the core even locally something weird would be bound to happen.{{citation needed}}

But Randall is afraid that their craving to get around that 20 mile wall would prevent the researchers from even hesitating if they did get that chance. Fortunately, we can study planetary cores in the solar system without stripping Earth's surface by visiting an asteroid which is thought to be the exposed iron core of a protoplanet. The {{w|Psyche (spacecraft)| Psyche mission}} is scheduled to launch in 2023 and arrive at {{w|16 Psyche}} in 2029.

This comics seems to be a spin-off from the previous comic [[2057: Internal Monologues]], where Randall tried to find some interesting monologues from scientist from different research fields. Maybe he did not find an internal monologue he liked for geologists, but ended up with this idea instead. Thinking about the core or mantle, lava and magma seems to be something Randall does a lot, and thus he must have some ideas about how a geologist would think, as in [[913: Core]].

==Transcript==
:[Ponytail is gesturing towards Megan with her hand, while talking to her.]
:Ponytail: I live next to a wall of rock 20 miles thick. There's no way around or over it. I'm trapped on this side forever.
:Ponytail: I study the stuff on the other side.

:[Caption below the frame:]
:Mantle geology seems like the most frustrating field.

{{comic discussion}}

[[Category:Comics featuring Megan]]
[[Category:Comics featuring Ponytail]]
[[Category:Geology]]