2792: Summer Solstice

2023-06-22T17:58:08Z

Kenneth: /* Explanation */ Improved eye safety warning.

{{comic
| number = 2792
| date = June 21, 2023
| title = Summer Solstice
| image = summer_solstice_2x.png
| imagesize = 238x373px
| noexpand = true
| titletext = 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==
{{incomplete|Created by a TOTAL SOLAR ECLIPSE ENJOYER- Please change this comment when editing this page. Do NOT look directly at the sun, unless at the short ''period of totality'' of a total solar eclipse (1 or 2 minutes). See [https://www.nasa.gov/content/eye-safety-during-a-total-solar-eclipse NASA's page] for details.}}
[[Cueball]] celebrates the northern {{w|summer solstice}}, which occurred on the day of this comic's release. [[Megan]] then comments on this by saying that there will be six days to the latest sunset of the year, to which [[White Hat]] exclaims ''Wait, what?'' - confused as to why these are not the same occasion.

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 vary by a few days. This is because Earth orbits the Sun in an ellipse, and its orbital speed varies slightly during the year, and due to the tilt of the Earth's axis, the sun has a different transit time across the sky depending on the season and latitude. The difference between the transit time of the sun and the mean solar time displayed on the clock can be as much as seven minutes. During the solstice this discrepancy is greatest. White Hat, a layman, 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 the sun will rise even later than previous days during those six days 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. And 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 thus earliest sunrise). This could be accomplished by either making Earth's orbit circular, or 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 {{w|solar eclipses}} from 0-1 each year to one each month. Solar eclipses occur when the {{w|Moon}} is directly between the Sun and Earth. Because of the tilt of the Moon's orbit to the {{w|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 ([[:Category:Total Solar Eclipse 2017|2017]]), and will soon get another ([[1928: Seven Years|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.

{{comic discussion}}

[[Category:Comics featuring Cueball]]
[[Category:Comics featuring Megan]]
[[Category:Comics featuring White Hat]]
[[Category:Astronomy]]
[[Category:Time]]

explain xkcd - User contributions [en]

2792: Summer Solstice