2792: Summer Solstice

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Summer Solstice

Title text: Then I'll start work on my lunar engines to line the Moon up with the ecliptic so we can have a solar eclipse every month (with a little wobble so they're not always on the equator.)

Explanation

This comic was released on the day of the summer solstice in the Northern Hemisphere.

The summer solstice occurs when one of Earth's poles has its maximum tilt toward the Sun. Although the summer solstice is the longest day of the year for that hemisphere, the dates of earliest sunrise and latest sunset differ by a few days. This is because of two different effects. First, Earth's axial tilt means that at some points in the year, the Earth is slightly ahead in its total rotation, whereas at other parts it is behind. Second, Earth orbits the Sun in an ellipse, and its orbital speed varies slightly during the year. These two effects combine to give the Equation of time, which relates variable solar time to steady clock time. Near the summer solstice, the two have competing effects, with the axial tilt making the days later and the orbit making days earlier. The axial tilt is the faster changing of the two at the summer solstice, so it wins out, meaning that sunsets are still getting later for a few days after the solstice, despite the days getting shorter. White Hat, a layman not aware of this correction, assumed that the latest sunset would occur on the summer solstice.

Similarly the earliest sunrise already happened before the solstice. This is given since the day (time the Sun is over the horizon) was longest on the solstice, but the Sun will set later for the next six days, meaning that during those six days the Sun will rise later than previous days by an even greater margin to make the days get shorter after the solstice.

The caption says that Randall is working on a giant machine capable of adjusting the Earth's orbit. Once finished, the first thing he will use it for is to fix this discrepancy, so the longest day will also have the latest sunset and earliest sunrise. This could be accomplished by either making Earth's orbit circular and removing the axial tilt (which would eliminate the solstices), or trying to balance the orbital eccentricity with the axial tilt, making the solstices match the days of closest or furthest distance from the Sun (perihelion or aphelion). This "fix" would avoid confusing people like White Hat.

The title text discusses his next plans for increasing the number of solar eclipses from 0-1 each year to one each month. Solar eclipses occur when the Moon is directly between the Sun and Earth. Because of the tilt of the Moon's orbit to the ecliptic (the plane of the Earth's orbit, as sort of depicted in 1878: Earth Orbital Diagram), most of the times when the Moon is between the Sun and the Earth they're not in direct alignment, so the Moon's shadow misses the Earth and we don't get an eclipse. Randall's engine will shift the Moon's orbit so it's not tilted so far and we get eclipses every month. But if it were exactly aligned with the ecliptic, eclipses would always be near the equator, so he'll leave a little wobbling so other areas will get eclipses too. Randall thinks solar eclipses are extremely cool, as noted in 1880: Eclipse Review, and would prefer that some of the eclipses will be visible from where he lives. He just had one six years ago (2017), and will soon get another (2024), but after that there will not be any eclipses over mainland USA for many years.

Transcript

[Cueball, Megan and White Hat are standing. Cueball and Megan have their arms raised.]

Cueball: Happy summer solstice!

Megan: Only six days until the latest sunset of the year!

White Hat: ...Wait, what?

[Caption below the panel:]

When I finally finish building my giant engine capable of shifting the Earth's orbit, this is the first thing I'm fixing.

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Discussion

Related to 1878: Earth Orbital Diagram? Purah126 (talk) 00:32, 22 June 2023 (UTC)

Great minds think alike*. Hadn't read down here when I leapt in and added that link (and made some other very minor tweaks). Or at least leapt in once I'd found it myself (not rembering its title or enough of its keywords), having had to trawl through Category:Astronomy and visit almost all likely titles and several unlikely ones. Which was enjoyable, so not a problem. ;) 172.70.85.92 00:58, 22 June 2023 (UTC) * - fools never differ... :P

I think there's a 3rd option for what the "fix" entails: eliminating Earth's axial tilt so it's always equinox (12 hour days almost everywhere, perpetual dawn at the poles). The title text specifies "on the equator", not "near" the equator. The only way for eclipses always "on" the equator is if the equator is always aligned with the ecliptic. - Frankie (talk) 02:06, 22 June 2023 (UTC)

Wouldn’t that cause a lot of trouble with stuff like crop growth patterns? —Purah126 (talk) 16:58, 22 June 2023 (UTC)

I think that to make the solstices match the earliest sunrise/sunset might require straightening out the Earth's tilt as well. Making it a circular orbit I think actually makes the summer solstice even further from the latest sunset (but the winter solstice closer to latest sunrise). [1]. Oh but straightening the tilt would mean no more solstices at all, hm. Maybe what's required is an elliptical orbit but with the sun at the center rather than a focus. --172.70.111.153 14:27, 22 June 2023 (UTC)

I think elliptical orbit with the Sun at the center is not stable. -- Hkmaly (talk) 23:05, 22 June 2023 (UTC)

Yes but he has an engine. --172.70.115.64 13:53, 24 June 2023 (UTC)

While we're at it, can we please make the year, lunar phase period, and day neat ratios of one another? 172.69.247.44 13:52, 22 June 2023 (UTC)

I'll email someone at NASA about it, don't worry. Trogdor147 (talk) 20:54, 22 June 2023 (UTC)

Should we make it 360 days/year (360 is a highly composite number) or should we go with 400, for easy multiples? Either then means we have to redefine the length of the week. I'm OK with 50 eight-day weeks. I propose the new day to be called Randallday. SDSpivey (talk) 21:51, 22 June 2023 (UTC)

Definitely 360, it would nicely match there being 3600 seconds in hour. Also, the bigger change you would do the worse effect would it have on biosphere. -- Hkmaly (talk) 23:07, 22 June 2023 (UTC)

Why? There would only be a small lengthening of the day (~1.5%), presuming the actual time length of the year is the same. BTW, do flatearthers call it a biodisc? SDSpivey (talk) 01:00, 23 June 2023 (UTC)

Will we get a vote on whether the moon orbit is 'fixed' to give us total eclipses, annular, or a mix of both?141.101.98.20 08:39, 23 June 2023 (UTC)

Anyone have any What If? type insights about any unintended consequences of the proposed changes? Thinking more of the physical and natural rather than societal, but anything might be an interesting addition to the article. 172.68.35.28 14:58, 22 June 2023 (UTC)

Tides, possibly ocean currents. Need a physicist for details (I'm a marine biologist; tides are on my radar, tide modeling isn't), but regularization of Earth and Moon orbits would remove many of the gravitational drivers of things like "spring" and "neap" tides, leading (it sez here) to permanent changes to littoral zones and their biotas, and (ditto) impacting coastal zone management strategies, especially if the "new normal" (and consistent) tides were much higher or lower than previous means. Arguably, an ocean biosphere already under stress from global warming would resent having to put up with yet another anthropogenic set of challenges. Hm? 162.158.186.169 16:41, 22 June 2023 (UTC)

Great Randal[l]s think alike... I had just posted this to Facebook a day before seeing Randall's work. RandalSchwartz (talk) 04:45, 23 June 2023 (UTC)

ALTER EARTH'S ORBIT AND TILT - STOP GLOBAL DISASTERS AND EPIDEMICS
ALTER THE SOLAR SYSTEM. REORBIT VENUS INTO A NEAR EARTH-LIKE ORBIT
TO CREATE A BORN AGAIN EARTH (1990)
-- Alexander Abian
BunsenH (talk) 17:56, 23 June 2023 (UTC)

So, "six days" does that mean June 28th, 2023 is the latest sunset of the year? I'm kind of shocked that there's not already a citation here showing this fact (if that's the actual day). Anyone? Ansarya (talk) 21:54, 23 June 2023 (UTC)

It may change according to the place. According to some ephemera, I have at hand, Edinburgh (Scotland) has its earliest sunrise on 18th June, latest sunset on 24th June. London (England) 17th and 25th June, respectively. Pittsburgh (PA) is 14th and 27th/28th. Milan (Italy) 15th/16th and 26th/27th, etc. Both latitude (effecting the moment the Sun's path dips below the horizon) and longitude (how the exactly cyclic patterns cross the shifted day/night cycle) interact. Which means that it's highly dependent on where the xkcd characters are. 172.69.79.159 23:01, 23 June 2023 (UTC)

Yup, total news to me that the summer solstice isn't both the earliest sunrise and latest sunset. :) NiceGuy1 (talk) 06:45, 24 June 2023 (UTC)

I'm pretty sure this fix is not right: "making the solstices match the days of closest or furthest distance from the Sun (perihelion or aphelion)". The axial tilt makes the length of a solar day longer at both the summer and winter solstices (a preceding paragraph of the explanation has that right). To balance this out by just changing the orbit, we need the Earth to be moving most slowly (which would normally be when it is furthest from the sun) at _both_ solstices. So it wouldn't work to have one solstice be perihelion and the other by aphelion. I think it is really the speed of the Earth that needs to be changed, and normally that is based on distance from the Sun, but not if you have an engine capable of altering it. So, if Randall wanted to maintain the axial tilt and thus the solistices, I think he would need to be continuously operating his engine in order to make the Earth's speed slower at the solstices and faster at the equinoxes. --172.70.110.60 14:02, 24 June 2023 (UTC)

Just occurred to me that the comic title is Summer Solstice so maybe he only wants to fix the summer (in Northern hemisphere) solstice and does not care if his fix makes the discrepancy even worse between the winter solstice and latest sunrise / earliest sunset? --172.70.114.17 14:41, 24 June 2023 (UTC)

Here is a good explanation for the differences between solstices and latest sunset: https://www.timeanddate.com/calendar/june-solstice.html