Editing 2897: Light Leap Years

Jump to: navigation, search

Warning: You are not logged in. Your IP address will be publicly visible if you make any edits. If you log in or create an account, your edits will be attributed to your username, along with other benefits.

The edit can be undone. Please check the comparison below to verify that this is what you want to do, and then save the changes below to finish undoing the edit.
Latest revision Your text
Line 10: Line 10:
  
 
==Explanation==
 
==Explanation==
 +
{{incomplete|Created by A FLEET OF PAPAL STARSHIPS FROM 1582 - Please change this comment when editing this page. Do NOT delete this tag too soon.}}
  
−
The comic features [[Cueball]] and [[Ponytail]] updating astronomical distances in a database. The caption imagines a world in which {{w|leap year}}s, 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 comic portrays [[Cueball]] and [[Ponytail]] updating astronomical distances in some sort of database, noting how long and unpleasant the process is; the caption reveals that the reason is that {{w|leap year}}s "make light-years 0.27% longer" (366/365 = 1.0027397...). This makes the distance to Alpha Centauri "0.27% shorter". 2024 is a leap year in the Gregorian calendar, and leap day (February 29) was just over one week away when this comic was released.  
  
−
The joke hinges on the fact that in most common usages years have a variable length, with the {{w|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 {{w|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 joke of this strip is based on the fact that "one year" isn't a precise unit of measurement: there have been different definitions, evolving over time, of what constitutes a year. The {{w|Gregorian calendar}} (the one most commonly used in modern times) includes a system of leap years in which an additional day is added every fourth year (with some exceptions) to make up for incompatibilities between day and year cycles. This temporarily changes the length of a year from 365 to 366 days.
  
−
The title text imaginatively claims {{w|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 [https://www.customcalendarmaker.com/leap-years ''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. {{w|List of adoption dates of the Gregorian calendar by country|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 {{w|light year}} is a unit of distance, commonly used in astronomy, equal to the distance light travels in a vacuum in one year; the year used is the {{w|Julian year (astronomy)|Julian year}}, or 365.25 days. This results in a light year which is standardized at 9,460,730,472,580.8 km, no matter how long the calendar year may be. However, in this comic, a light year has been defined based on the length of the ''current'' year, and consequently becomes longer during leap years, meaning databases with astronomical distances have to be adjusted. Thankfully, most systems of measurement do not change continually, and even those those that do (eg. DST) usually are setup to automatically update when necessary.
  
−
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 {{w|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 {{w|Scilly naval disaster of 1707}} in which four ships were lost and over 1,400 sailors died due to navigational errors.
+
The title text jokes that {{w|Pope Gregory XIII}}, the originator of the Gregorian calendar, "briefly shortened the light-year in 1582." What really occurred in 1582 was that the Pope decided to advance the previously Julian calendar by 10 days to make up for an accumulated excess of past leap days and bring the subsequent Gregorian one more into line with astronomical measurements. Not all places went with the change, at that time. Some of the later adopters had to {{w|List of adoption dates of the Gregorian calendar by country|skip yet other days once they did}}, while others continue to use a calendar with an offset factor. In the world of the comic, this change led to "navigational chaos and the loss of several Papal starships". This is of course ludicrous since there were no (known earthly) starships in the 16th century, there has never been a "Papal starship",{{Citation Needed}} and the light-year wasn't developed as a unit of measurement until 1838. Indeed, it wasn't known that the speed of light is finite until {{w|Rømer's determination of the speed of light}} in 1676. Navigational chaos ''has'' been a cause of shipwrecks, notably the {{w|Scilly naval disaster of 1707}} in which 4 ships were lost and over 1,400 sailors died.
  
−
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.
+
The joke is that the evolving and somewhat loose and changing definitions of early calendars had significant impacts on the units of measurement we still use today. Such changes did serve to catalyze political and religious conflicts in some instances, and raised temporary issues around matters such as taxes, rents, etc., but as technology has advanced and become increasingly reliant on precise and consistent measurements, they could be significantly more disastrous.
  
−
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 {{w|International Astronomical Union}}, which is only minutely different from 4.2465 light-years, the value given by {{w|Gaia catalogues|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).
 
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 {{w|International Astronomical Union}}, which is only minutely different from 4.2465 light-years, the value given by {{w|Gaia catalogues|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 {{w|parsec}} ("''pc''", or useful multiples such as ''kpc'', ''Mpc'', or ''Gpc''). One of those is approximately 3.24 light years, so has a [[2205: Types of Approximation|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 {{w|Light-year#Related units|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==
 
==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 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 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!
 
:Cueball: It took until February, but I finally got all the distances updated!
 
:Ponytail: I really wish we didn't have to do this.
 
:Ponytail: I really wish we didn't have to do this.
 
:[Laptop screen:]
 
:[Laptop screen:]
 
:<u>Proxima Centauri</u>
 
:<u>Proxima Centauri</u>
−
:Distance: [in red, crossed out] <span style="color:red"><s>4.2493 ly</s></span>
+
:Distance: <span style="color:red"><s>4.2493 ly</s></span>
−
:[in green] <span style="color:green">4.2377 ly</span>
+
<span style="color:green">4.2377 ly</span>
  
 
:[Caption below the panel:]
 
:[Caption below the panel:]

Please note that all contributions to explain xkcd may be edited, altered, or removed by other contributors. If you do not want your writing to be edited mercilessly, then do not submit it here.
You are also promising us that you wrote this yourself, or copied it from a public domain or similar free resource (see explain xkcd:Copyrights for details). Do not submit copyrighted work without permission!

To protect the wiki against automated edit spam, we kindly ask you to solve the following CAPTCHA:

Cancel | Editing help (opens in new window)

Templates used on this page:

Retrieved from "https://www.explainxkcd.com/wiki/index.php/2897:_Light_Leap_Years"