Editing 2971: Celestial Event

{{comic
| number    = 2971
| date      = August 12, 2024
| title     = Celestial Event
| image     = celestial_event_2x.png
| imagesize = 471x300px
| noexpand  = true
| titletext = If we can get a brood of 13-year cicadas going, we might have a chance at making this happen before the oceans evaporate under the expanding sun.
}}

==Explanation==
{{incomplete|Created by a CURSED SHOP THAT APPEARS EVERY FOUR POINT THREE BILLION YEARS - Please change this comment when editing this page. Do NOT delete this tag too soon.}}

This comic was posted shortly after some people reported seeing the aurora in conjunction with the perseids meteor shower.<ref>https://www.msn.com/en-us/weather/topstories/the-2024-perseid-meteor-shower-and-northern-lights-overlapped-in-a-rare-cosmic-display-see-photos-of-the-dazzling-event/ar-AA1oJKKC</ref> It lists several events that are considered special to be witnessed due to their rarity. Total solar eclipses, auroras and comet sightings are all rare events. This year, all three of these events happened in parts of Massachusetts, United States, where the author lives. 

Although it might be, conceivably, possible to witness all three at once in a given location (in this case, the author's neighborhood), the odds stack up to make that occurrence extremely improbable. To boot, those events can only be observed with a clear sky (a 50:50 chance), so that too has to be accounted for in the calculation.

"Total eclipse" presumably refers to total solar eclipses, as total lunar eclipses are visible from any side of the earth that the moon is visible. Using [https://eclipse.gsfc.nasa.gov/JSEX/JSEX-index.html this nifty tool from NASA], we can estimate the frequency of solar eclipses for a given location. For example, for the city of Boston, MA, there are 14 total solar eclipses in a 4500 year interval, an average of once every 320 years, which is close to the author's estimate. It must be noted that the author did not include annular eclipses, possibly because it would be harder to witness the aurora and the comet sighting during those. Also, unlike the other factors, the 1/350 implies that a total eclipse can be seen for the whole year, when in fact that variable would be (when generous) a mere hour every 350 years.

17-year {{w|Periodical cicadas|cicadas}} are also special in the sense that a brood will only emerge from the ground once every 17 years. Periodical cicadas recently became the object of media furor in 2024 as a 13-year brood and a 17-year brood happened to emerge together in parts of the US, an event that for the same two broods only happens once every 13x17 = 221 years. This caused a lot of noise and double the amount of dead cicadas after they had mated. Needless to say, having a cicada emergence co-occur with all those previously mentioned events would be extra rare, and thus extra special.

How rare, exactly, is the point of this calculation. The resulting product is the expected frequency that all of them would occur at the same time at that location. The value he calculates is once every 4.3 billion years. This is in the same ballpark as the current age of the Earth, about 4.5 billion years.

There are multiple inaccuracies in this type of calculation (though, given the extravagant nature of the proposed event and the unfeasible time scale, perhaps that hardly matters). Multiplying probabilities only works for random variables that are entirely independent. If nothing else, orbits are (luckily<sup>[<em><span style="color:#1144aa !important; ">maybe</span></em>]</sup>
) not random.{{cn}} It also requires that all of the probabilities remain constant over time. In reality, cicadas will not exist for very long compared to the time scale, since Earth will become uninhabitable to complex life within a billion years' time and all life will be extinct within {{w|Future of Earth|4 billion years}}. Also, the moon is moving away from Earth, and total solar eclipses will cease to occur in about [https://www.space.com/37627-total-solar-eclipse-earth-moon-alignment-future.html 600 million years]. Luckily, this is not the time that you are ''always'' going to wait, merely the (usual) period between one occurance and the next. A person starting to wait at a random point in the cycle, and not knowing anything else, would ''on average'' only have to wait ''half'' the time. (If very lucky, it could happen tomorrow, as it hypothetically might have done a bit over four billion years ago; if unlucky, it would indeed be slightly more than four billion years, having most recently happened yesterday; if ''very'' unlucky, the frequencies are slightly less defined, do not actually align as expected for the next conclusion of the cycle and additional billions of years need to be waited until the next example when it 'might' indeed occur as anticipated. Finally, if '''extremely''' unlucky, you will never get a clear sky. Ever.

In order for the math to work out, some unit conversion is necessary. To solve "20 days / 11 years", one can consider 1 year = 365.24 days (a reasonable approximation that accounts for most leap years). For "2 months / 50 years" and "2 months / 17 years", the simplest way is to convert 1 year into 12 months. Unit cancelation works out, and you end up with a number in years that corresponds to the average amount of time between events when all those different things are happening at once. (the implied unit for eclipses is events per year, and that's the unit you get as a result, so the actual length of the eclipse doesn't influence the result much).

In the title text, Randall mentioned swapping 17-year cicada broods for 13-year ones, to have some chance at witnessing the proposed super-event before life on Earth becomes impossible. Massachusetts is near the northern limit of {{w|Periodical_cicadas|<em>Magicicada</em>}} distribution, and only one 17-year brood is established there (and not in Cambridge, MA). However, the introduction of a different brood could, with some help from global warming, be feasible. There are other variables that are possibly available for manipulation: clear skies can be arranged with various methods of {{w|Weather modification|weather control}}; special cicada broods may be bred or bioengineered specifically to coincide with the other factors of the celestial event; and while the aurora cannot currently be manipulated by humans, there may be artificial methods to make it possible.

Earth's oceans may evaporate in about one billion years<ref>https://www.sciencedaily.com/releases/2013/12/131216142310.htm</ref>. In order to beat that, we need to better our odds. Using 13-year cicadas in our calculations reduces the average interval between events to 3.29 billion years. We can lower that further by hoping that we'll have clear skies by then (who knows, we might get good enough at manipulating weather that we can *make* it happen). That gives us an average interval between events of about 1.6 billion years. Which means a larger than 50% chance that we'll get our special super-event to happen within a billion years, therefore beating ocean evaporation. Of course, cicadas may not last that long.<sup>[<em><span style="color:#1144aa !important; ">baseless conjecture</span></em>]</sup> <sup>[<em><span style="color:#1144aa !important; ">trust the cicadas</span></em>]</sup>

==Transcript==
{{incomplete transcript|Do NOT delete this tag too soon.}}
:<u>Approximate frequency in my area</u>

:Active northern lights: 20 days per solar cycle

:A naked-eye "Great Comet": 2 months every 50 years

:Total eclipse: once every 350 years

:Clear skies: 50% of the time

:17-year cicada emergence: 2 months every 17 years

opening bracket

20 days over 11 years multiplied by 

2 months over 50 years multiplied by

1 over 350 years multiplied by

one half multiplied by

2 months over 17 years 

closing bracket to the power of -1

equals 4.3 billion years

:[Caption below the panel:]
:Every 4 billion years or so, my neighborhood gets to see a ''really'' spectacular show.

{{comic discussion}}

[[Category:Astronomy]]
[[Category:Solar eclipses]]
[[Category:Time]]
[[Category:Animals]]