# 2897: Light Leap Years

 Light Leap Years Title text: When Pope Gregory XIII briefly shortened the light-year in 1582, it led to navigational chaos and the loss of several Papal starships.

## Explanation

The comic features Cueball and Ponytail updating astronomical distances in a database. The caption imagines a world in which leap years, which add an extra day to the year, making it 366 days long instead of 365, purportedly extend light-years by 0.27% due to the additional day (366/365 = 1.0027397...). This adjustment ostensibly reduces the number of light years to celestial bodies like Alpha Centauri by a corresponding percentage — a relatively small amount, but one that corresponds to approximately 730 times the average Earth-sun distance. The comic was released about a week before the leap day of 2024, a leap year.

The joke hinges on the fact that in most common usages years have a variable length, with the Gregorian calendar's leap year system — adding a day every four years to align the calendar year with the astronomical year — being the current civil standard in most of the world. A light year, defined in astronomy as the distance light travels in a vacuum over a Julian year (365.25 days), remains constant at 9,460,730,472,580.8 km, unaffected by the Gregorian calendar's leap years. However, the comic amusingly suggests that leap years lengthen light years, necessitating database updates for astronomical distances.

The title text imaginatively claims Pope Gregory XIII, who introduced the Gregorian calendar in 1582, inadvertently affected the length of the light-year. This is not due to 1582 being a leap-year (it was not a leap-year), but because of the calendar days that had to be skipped to remove the timing error built up when using the prior (and less correct) Julian method of leap-years. Those adopting the system in 1582 had to shorten this year by ten days. Later adopters may have had to shorten the year that they did change by up to 13 days, i.e. up to three extra days for every four whole centuries spent on the 'wrong' calendar.

A year of effectively 355 days, rather than 365, would therefore lead (by this comic's premise) to potential misunderstandings/misapplications of distance approaching 3%, leading to "navigational chaos" and the loss of "Papal starships." This satirizes the significant historical impact of calendar reforms on navigation and measurement, despite the anachronism, as the light-year wasn't defined until 1838 and the concept of a finite speed of light only emerged in 1676 with Rømer's determination of the speed of light, whilst practical starships (papal or otherwise) that would usefully rely upon light-year measurements, have yet to be developed (on Earth, at least, the only place where such light-year measurements might originate). However, navigational chaos has been a cause of maritime shipwrecks, such as the notable Scilly naval disaster of 1707 in which four ships were lost and over 1,400 sailors died due to navigational errors.

Alternatively, the title text could be interpreted as a joke about how the light-year in astronomy is based on the Julian year (365.25 days) rather than the mean Gregorian year (365.2425 days). The pope may have briefly changed that definition, leading to "navigational chaos". Although the difference between a Julian light-year and a Gregorian light-year is only about 20 parts per million, it still amounts to about 194 million km (121 million mi) per light year.

This is another comic, after the very recent 2888: US Survey Foot, about how differing interpretations of standard units could have absurd real-world implications.

### Discussion of the use of light year values in the comic

The values given for Proxima Centauri's distance from the Sun, 4.2377 light-leap-years and 4.2493 light-nonleap-years, are consistent with a distance of 4.2464 actual light-years as described by the International Astronomical Union, which is only minutely different from 4.2465 light-years, the value given by Gaia Data Release 3 in 2020. Though tiny on an interstellar scale, the difference between 4.2377 and 4.2493 light-years, 0.0116 light years, equals 109.7 billion km (68.2 billion miles), about 730 times the average distance between the Earth and the sun (150 million km or 93 million miles).

Ironically, this kind of change would not actually bother astronomers in the slightest. Astronomical distances on scales larger than the solar system are universally (or rather, globally: we do not know how things are done in other parts of the universe) measured with the parsec ("pc", or useful multiples such as kpc, Mpc, or Gpc). One of those is approximately 3.24 light years, so has a similar astronomical magnitude, but is founded upon common interpretations of distance and angle instead of time. (Both partly rely upon baseline measures that are complementary aspects of Earth's orbit, i.e. its periodicity and radius, which theoretically make for a globally agreeable system; but highly unlikely to match whatever equivalent any non-terran scientists would independently develop.) While light-years, and related units, are common in publications intended for non-astrophysicists and for the benefit of laypersons, they are generally considered as secondary usefulness to parsecs within the actual fields of astronomy and astrophysics research. As such, it is highly likely that the clearly exacting database that Cueball and Ponytail are in the process of modifying is not even keyed to any light-units, making leap-/non-leap-light-years already an automatic conversion that the system may pander for without such a direct interaction.

## Transcript

[Cueball is sitting at a desk with a laptop on it and leaning to the back of his office chair, while having his other hand on the laptop. He is looking at Ponytail, who is standing behind him. The text from the laptop screen is shown above it, indicated with a zigzag line.]
Cueball: It took until February, but I finally got all the distances updated!
Ponytail: I really wish we didn't have to do this.
[Laptop screen:]
Proxima Centauri
Distance: [in red, crossed out] 4.2493 ly
[in green] 4.2377 ly
[Caption below the panel:]
Astronomers hate leap years because they make light-years 0.27% longer.

# Discussion

Not that it effects the joke, but the Gregorian calendar has 97 leap years per 400 year cycle. I was surprised that I was surprised by that. 162.158.63.115 16:23, 21 February 2024 (UTC)

Another interesting number: the difference between the standard Julian year and the (AFAICT, not officially named as such) 'standard Gregorian year' (of 365.2425 days) is 648 seconds, or 10.8 minutes (10m48s) if you prefer. 172.69.194.115 00:38, 22 February 2024 (UTC)

"...never been a papal starship..." - If this upsets you, read Hyperion! 172.71.142.67 17:12, 21 February 2024 (UTC)

Even the most cursory research (i.e. googling) reveals that there have been Papal starships.172.70.90.190 09:38, 22 February 2024 (UTC)
I appreciate the {cite needed}!!! and added more adjectives (known earthly). Just because we are not aware of any, doesn't mean they don't exist! For example, how did Michelangelo get to this planet? I have my suspicions!!!;P Cuvtixo (talk) 01:57, 23 February 2024 (UTC)
Could also be a Doctor Who reference, the Papal Mainframe being a space station featuring in "The Time of the Doctor". 172.69.43.220 10:42, 23 February 2024 (UTC)

"Note: Lightsecond was chosen instead of the more familiar lightyear to make sure that layouts computed during leap years would be unambiguously identical to those computed during non-leap years." (from https://drafts.csswg.org/css-egg-1/#astro-units) --172.68.253.143 18:23, 21 February 2024 (UTC)

The last paragraph says Randall. It should say Cueball. Randall knows better otherwise he would not have made this joke. 172.71.22.98 04:02, 22 February 2024 (UTC)

I find it funny (assuming we're seeing the last edit to have been done, and Cueball's not just scrolled us up to see the very first 'diff' again) that the whole month-and-a-lot-long job has apparently finished with the changed measurement for the likely closest object in the database of thousands (or maybe even "millions and billions!") of cosmological objects. Whether or not it has extragalactic (or significantly transgalactic) record items in it, it would seem rather topsy-turvy to leave the physically nearest item's entry until last, if it was indeed consciously sorted by any distance-related parameter. (Like I could understand if it were perhaps something like Zeta Reticuli, where we ended up, more than Alpha Cassiopeiae, or maybe Z Vul at the opposite end to 'Alpha And'.) ...ok, so maybe now I'm just dissecting the frog toad, but I still think it's yet another 'layer of funny'. Whether intended (I really wouldn't put it past Randall being so deep...) or otherwise! 172.71.178.185 03:04, 24 February 2024 (UTC)

Question 1: What is incomplete about this article? Question 2: When it's complete, can we somehow preserve the papal starships from Anno Domini MDLXXXII? GreatWyrmGold (talk) 15:23, 5 March 2024 (UTC)