2725: Sunspot Cycle

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Sunspot Cycle
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.'
Title text: 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.'


The solar cycle is a roughly 11-year cycle of changes in the Sun's activity (sunspots, solar radiation, ejecta, and solar flares), from a period of minimal activity to maximum solar activity. Researchers use specially modified telescopes to study the sun. Sunspots are areas on the sun which are slightly less hot than the surrounding material, so they appear as dark patches when viewed through these telescopes, but they do not meaningfully impact the amount of light that reaches the Earth.

This comic imagines an alternate reality where sunspots are literally black patches on the surface of the sun, void of all luminance, so the amount of light that the Earth receives swings drastically over an 11-year cycle. As the text above the chart suggests, the inhabitants of Earth in this reality are so accustomed to the extreme decade-long cycle of darkness and light that they don't even consider why it's pitch black for 10 years straight, and so Randall helpfully created this chart to explain.

Below is a graph showing the number of sunspots as a function of time from around 1965 to 2025. During the periods of heightened solar activity, the area of the graph is shown in black, while lighter periods are shown as white. 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 during the height of the transition between the two extremes, with a wide swathe of the time around the minima being mostly light or mostly dark, alternating at around a decade of each predominating.

All this would obviously be catastrophic if it happened in our version of the universe, as during a dark phase insufficient light would be coming from the Sun, and the Earth could freeze if all the energy from the Sun was reduced. If the spots only affect light in the visible spectrum, then Earth would not freeze but plants would have trouble with photosynthesis and other natural processes would be interrupted. In our universe sunspots cool the area of the Sun where they appear, relative to the rest of the surface (50-75% of the nearly 6000K 'norm'), but they are far from being actually dark; NASA says that each sunspot on its own would glow orange, brighter than the full Moon. So even in a completely sunspot-covered Sun, the Sun would still be brighter than (with a typically bright Sun illuminating it) the Moon, and far brighter than the dark-time Moon would become (possibly causing issues for nocturnal life, as well). It would be possible to see it (and see by it) even if the heat delivered were very low and even noon would seem to be crepuscular by our normal expectations. These problems are obviously not a serious threat in the reality of the comic, as the Sun is truly dark and yet people and natural systems have long survived these dark periods and adapted accordingly.

The title text indicates the effect on internet memes that the special solar cycle has had. 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 90s and before would remember dawn or the feeling of the warm sun on their faces.

Sunspot cycles were discussed in 2930: Google Solar Cycle.


[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 no 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 it 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 are 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

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Holy cow, just made my first edit! It was SUPER stressful, and I didn't even know how to make a 'citation needed' thing. Hopefully it was ok, I tried to match the style of the wiki. GordonFreeman (talk) 03:06, 17 January 2023 (UTC)

Welcome to explain xkcd then. Any edit that is not vandalism is a good edit, because it makes other think about what should be here. So even if it is later completely changed it got things going. --Kynde (talk) 08:05, 17 January 2023 (UTC)
I know that editing may be hard. FYI: create [citation needed]s like this: {{Citation needed}} PoolloverNathan[talk]UTSc 17:08, 17 January 2023 (UTC)
Though over-use should be discouraged. Except in exceptional circumstances (many different things separately explained, giving a number of prime opportunities) I'd avoid more than one Citation Needed per comic. And I personally think (and it is the official intention) that trying to find even one 'suitable' item per comic devalues the joke, perhaps should be (on average, but not punctually so just for the sake of it) maybe one for every three or four such pages; but I know there are those who would want to stamp (at least!) one into every comic, just because they can. And I would not normally remove an instance just because its usage is comparatively weaker than those in the two adjacent articles.
And note that there are redirecting versions of {{citation needed}}, {{cn}} and {{fact}} (amongst others) in case you can't recall that it is "Capital C, small n" or are forgetful/lazy as you try to type it, though I think using the non-redirecting original should be done if you know how to fully write and capitalise it (feels neater). There is also {{Actual citation needed}} when the 'real thing' is needed; though in a manner where you expect that issue to be resolved and removed by the next person who can either actually 'cite' what is true or else remove the properly doubtful information.
Anyway, I shall add my thanks to the original Explainer, it was a good first job, IMO. 13:50, 18 January 2023 (UTC)

Is it perhaps worth mentioning that sunspots, while they're darker than the rest of the sun's surface, are not actually black. They are cooler than surrounding regions and appear dark by contrast, but they're emitting lots of IR and some visible light. A sunspots-only (ignore the oxymoron) sun would still emit light and heat, just less. Nitpicking (talk) 03:18, 17 January 2023 (UTC)

Wouldn't the cycle be 20 ("every other decade") or 22 years (11 in each half of the cycle)? 03:51, 17 January 2023 (UTC)

The cycle of darkness of the sun would be 22 years, but the 11-year cycle referred to in the comic, and described by both diagrams within the comic, is the cycle of "number of sunspots" which peaks when the sun is half light, half dark, and decreases again as there are so many spots that they start to merge into fewer, larger spots. It cycles from very few (or zero) sunspots, when the sun is light, through many sunspots, sun is heavily light/dark spotted, and completes the cycle when the number of spots returns down to near-zero, when the sun is dark. (talk) (please sign your comments with ~~~~)
Or to put it another way, at "peak sunspot" every 11 years, it would be equally accurate to describe the sun as being bright with dark spots or dark with bright spots. Akin to how the moon has a 29.5 day brightness cycle, but also a 14.75 day halfiness cycle. 16:57, 17 January 2023 (UTC)

To what "financial crash of 2014" does this refer? I recall the housing crisis causing financial trouble, but that was around 2008. 03:51, 17 January 2023 (UTC)

This has nothing to do with finance so if you think the peak at 2014 should have any meaning I think you are wrong. there where just for some reason more sunspots even though the sun was still in the dark period. Maybe most of the few huge sunspots broke into smaller but with only thin lines between, so still dark but the count goes up. Then they closed again later keeping the sun dark but the number of spots fluctuating. --Kynde (talk) 08:05, 17 January 2023 (UTC)
It was a question about explanation text that was added in this revision and removed about half an hour later. 03:33, 18 January 2023 (UTC)

Does anyone have any idea what is supposed to be on the Y axis of the bottom graph? Something that goes up when the sun is transitioning between brightnesses and is at its lowest when the sun is either fully bright or fully dark? (talk) (please sign your comments with ~~~~)

It's the "number of spots" (whether light or dark), since a fully bright sun has no dark spots and a fully dark sun has no "light spots"Dextrous Fred (talk) 05:02, 17 January 2023 (UTC)
But what are the thin lines indicating, it it just to show that the sun is not yet really dark? Like a gray shade with very long between the dark lines? --Kynde (talk) 08:05, 17 January 2023 (UTC)

Did anyone else notice that the sine-wave is wrong? the trough should be the same every cycle, yet it's drawn as bright in the first trough and dark in the second trough. -Weylin Piegorsch 06:52, 17 January 2023 (UTC)

If you reefer to the bottom graph it is correctly drawn. The sunspots number are near zero when the sun is bright in the first through and then it is again near zero when the sun is dark as there are then only one sunspot. So that is why it is alternating between light and dark for every through. Just as shown in the upper graph. --Kynde (talk) 08:05, 17 January 2023 (UTC)--Kynde (talk) 08:05, 17 January 2023 (UTC)
Ah - the y axis of the upper graph is #subspots (which maximizes as they merge and minimizes at full dark/full bright), not magnitude of brightness. Thanks for the clarification! -Weylin Piegorsch 14:47, 17 January 2023 (UTC)

I do not think it is set in an alternate universe per se, but in the images of the sun spots the minimum brightness of the whole sun is subtracted. So only the sun spots stay visible. So the sun images are depictions of our sun. The number of sun spots loses common-sense meaning after merging starts. Sebastian -- 07:58, 17 January 2023 (UTC)

Well since the sun is dark in this universe for 10 years, then it cannot be our universe, and since they also have 90s memes, then it is either a parallel universe or well... Randall's fantasy :-) --Kynde (talk) 08:05, 17 January 2023 (UTC)

I didn't have enough space in my last edit summary to explain my change. As if anyone who needs to really reads those, anyway... So here (unconstrained by petty character limits!) is why I took off the apostrophes in "90's kid", etc...:

/* Explanation */ Removing apostrophes not used by Randall. (I would personally say '90s, the apostrophe being for the contraction of 1990s, but here only the quoting-apostrophes of '90s kid' seems necessary and capable of being consistent. "The 90s" is a pluralisation of all years of the decade based upon (19)90. A kid *of* the 90s could be a 90s' kid, but I think we're intended to treat this as an adjectival descriptor, not a posessive element.)

And I outright reject the idea that apostrophes can ever be used for pluralising, despite some 'authorities' on the matter. Especially where it clashes with plural-possessive, contraction and single-quoting uses in a single case, upon a wiki where doubled-up apostrophes would incite italics. Better to rewrite. But, for now, I've just rationalised to go with actual demonstrated usage (both from Randall and more or less in general) and intent. 10:27, 17 January 2023 (UTC)

Well, I don't think there's any value in spending 000's of hours debating it. 15:13, 17 January 2023 (UTC)

Does this remind anyone else of oscillations in population dynamics (increase in population eventually causes overpopulation and triggers a period of reduction before the population starts to recover, etc.)? 15:24, 17 January 2023 (UTC)

I had thought to say that a budding sunspot would become 'dark' if it was forming on light surface and 'light' if forming on darkened surface, which has a relationship with some biological population frequencies/responses (even within the same population, an expressed variation can be linked to the perception of what is/is not lacking in its fellows or just various overlapping territories). But a simple scenario (of instantaneous points; having the choice of locale to materialise, or else the accident of 'birth' into any given situation from which to sway their appearance) would settle into an equilibreum as a slightly more than half-dark Sun would spawn proportionately more 'light spots' than a slightly more than half-light one.
It needs to have a time-delayed aspect (as with natural creature populations, a post-gestation glut being based upon pre-gestation plenty; or upon the opposite negatively influencing pressures), so budding might start (and be fixed into its identity) years before it becomes a visible member of the population. A resonant hysteresis, of some kind? 16:20, 17 January 2023 (UTC)

Is there a way to shrink the size of the comic?[edit]

Is there some way to shrink the size of the comic? It startled me a little bit when I typed in the URL of this website and saw this taking up a large amount of space, with me initially thinking that this was just another stupid case of vandalism. SilverTheTerribleMathematician (talk) 16:32, 17 January 2023 (UTC)

Fixed PoolloverNathan[talk]UTSc 17:07, 17 January 2023 (UTC)

This comic me think of the long seasons of Westeros in A Song of Ice and Fire. Mnl (talk) 00:02, 18 January 2023 (UTC)

Should we say anything about the weird aliased version of this comic that went up originally? 01:08, 18 January 2023 (UTC)

The alternately dark and bright sun is very reminiscent of the OnOff star in Vernor Vinge's novel A Deepness in the Sky, although the duty cycle of the OnOff star is very different, spending 215 years "off" and 35 years "on" in a 250-year cycle. The On-Off Star even has an planet that is Earthlike and habitable, at least during the times the OnOff star is "on". Somehow life on that planet evolved to cope with the cryogenic freezing temperatures (the atmosphere actually freezes to the surface) when the star is "off" and is inhabited by an intelligent race of arachnid-like creatures. Stevev (talk) 08:31, 18 January 2023 (UTC)

For different astronomical reasons, it made me mostly think about the Helliconia series by Brian Aldiss. 13:50, 18 January 2023 (UTC)

Someone put the following in the Incomplete tag. I don't think it's right (a 7 year cycle... Could have been fudged to somehow happen three times in every two solar-cycles to more closely match..?) but it deserves to be seen in the context of every other potential inspirational source being mentioned:

Title text is a clear allusion to Bradbury's "All Summer in a Day" which is about the sun coming out every 7th year on Venus, an event which only Margot can remember. https://en.wikipedia.org/wiki/All_Summer_in_a_Day

...also, that editor should have tried using the site-standard {{w}} method for the link, perhaps, if they're reading this. For your future info, ok? 01:17, 19 January 2023 (UTC)

We now have a counterexample for "The sun is bright, and its light illuminates the Earth [citation needed]", which is from comic 285 19:22, 18 January 2023 (UTC)