2549: Edge Cake

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Edge Cake
Every time IERS adds or removes a leap second, they send me a birthday cake out of superstition.
Title text: Every time IERS adds or removes a leap second, they send me a birthday cake out of superstition.


Megan—possibly an IERS (International Earth Rotation and Reference Systems) agent—wishes Emily, represented as Hairbun, Happy Birthday. This prompts a confused Cueball to ask if her birthday was sometime last month. Emily explains that she was born over the North Pole in a plane, meaning that she was born in every timezone at once. Technically though this is false, as there are some timezones (such as UTC+5:45) that are not represented at the north pole. Except for the one hour before it's midnight at the International Date Line, the date in eastern time zones is one day ahead of western time zones, so Emily would have been born on two days at once.

She also says that it was February 29th (presumably it was also February 28 or March 1 in some time zones). February 29th only happens at most once every four years in the Gregorian calendar, adding to the confusion - people born on February 29th often celebrate their non-leap-year birthdays on arbitrary days (or not at all). Normally one could simply use the time zone of the city the airplane took off from, but the airline company was changing ownership from one country to another at the time, so this option has apparently been ruled out. This is not terribly logical, however, since contracts transferring ownership usually specify an exact time (commonly one minute before or after midnight in a specific time zone to avoid confusion on which day midnight is in) to come into effect. Regardless of which time zone(s) she was in when she was born this is an absolute time and if she was born before it she would have been born in an aircraft of the first country and if after it in an aircraft of the second country. Alternately, the time zone of the city the aircraft took off from doesn't change even if the nationality of the plane changes in midair, so that should have still been an option.

The punchline is that rather than try to identify the correct birthday for Emily, the BIPM has decided to let her have birthdays whenever she wants. This doesn't make much sense, however. As noted above even if she was born in every time zone at once it could only have been on one of two days (February 29th, plus either February 28th or March 1st). Since it is common for people born on February 29th to celebrate on February 28th in non-leap years, it would have been trivial to pick the non-leap day present in some of the time zones (either February 28th or March 1st) and declare it Emily's birthday. It's possible that Emily was told "You can choose when you want your birthday to be", and Emily decided to exploit the lack of specificity to the degree presented in the comic.

In real life researchers in the Arctic at or near the North Pole use Coordinated Universal Time as the local time standard by convention, to avoid this exact problem. Thus it could have been said that Emily was born on the date that it was at that time in UTC. Furthermore, it is extremely unlikely that she would have been born at the exact instant the plane was over the north pole, indeed, it is unlikely that the plane even traveled over the exact pole, as opposed to a few miles or even feet to either side of it. With modern positioning equipment such as GPS, it should have been possible to determine which time zone the plane was in when she was born. Even in the impossibly unlikely event that she was directly above the pole at the instant of her birth, at jetliner speeds the plane was traveling about ten miles per minute, so a reasonable delay of even seconds in declaring "time of birth" would have placed the plane and her clearly in one time zone.

Both the comic title and Cueball's final line are puns on "edge case", an engineering term referring to situations or conditions that are unusual in a way likely to cause problems unless specifically accounted for. Edge pieces are generally only important with sheet goods (brownies, sheet cakes, etc), which are typically cut into pieces creating a difference between pieces originating on the edge and pieces originating from the center. Since the top and sides of a cake are often frosted, an edge piece has two faces covered in frosting and a corner piece has three, while a center piece only has one. Depending upon your relative preferences between the surface (often icing over marzipan) and core body of the cake (which can be fruitcake, or some variety of spongecake, etc, but not actually obvious which until the cake is cut), it being an edge-faced slice can be considered a bonus. Cueball certainly seems to appreciate this.

The title text states that the IERS sends Emily a cake every time they add or remove a leap second, out of superstition (perhaps Megan is delivering that cake). The International Earth Rotation and Reference Systems Service is in charge of global time standards. It occasionally adds one leap-second to Coordinated Universal Time to adjust for changes in the rotation speed of the Earth.

The comic might also be a modern version of the SS Warrimoo, a passenger liner that reportedly crossed the international date line at the equator on midnight Dec. 31, 1899. This would have placed her bow in the Southern Hemisphere on 1 January 1900, her stern in the Northern Hemisphere on 31 December 1899. She would therefore have been simultaneously in two different hemispheres, on two different days, in two different months, in two different years, in two different decades, and according to some definitions in two different seasons (northern winter and southern summer) and possibly in two different centuries.


[Megan is walking towards Cueball and Emily (who resembles Hairbun), holding a cake.]
Megan: Happy birthday, Emily!
Cueball: Wait, wasn't that last month? When's your birthday, anyway?
Emily: It's complicated.
[A diagram of a flight path over the North Pole, with meridian lines radiating out from the center. Emily's dialogue appears above the diagram, but she herself does not appear in this panel.]
Emily: My mom went into labor on an arctic international flight that diverted directly over the North Pole.
Emily: I was born in every time zone at once.
[With Megan standing behind her, Emily holds out a plate of cake to Cueball.]
Emily: It was also February 29th, and the airline was just changing ownership between countries.
Emily: The International Bureau of Weights and Measures finally issued a declaration that it's my birthday whenever I want.
Emily: Cake?
Cueball: Nice, it's all edge pieces.


  • Hairbun was last named "Emily" in 788: The Carriage.
    • More specifically, that version of Hairbun represented Emily Dickinson, a real, historical person who had no such issues regarding her birthday.

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The cake being all edges is a reference to everything about her birth being an edge case. 03:41, 2 December 2021 (UTC)

It seems likely that the title of the comic is a related pun: her birthday is an edge case, and so she has an edge cake. 04:22, 2 December 2021 (UTC)

So is Hairbun officially named Emily now, sort of like how all instances of Megan are Megan even though she's only called that once? I know all the names here are just placeholders of convenience, but even then I've never know what the rules for naming are. Captain Video (talk) 06:11, 2 December 2021 (UTC)

Well, Megan is referred to multiple times in the xkcds as "Megan", while the one time Hairbun was called Emily, it referred to the real[citation needed] Emily Dickinson. So, probably not. bubblegum-talk|contribs 02:44, 3 December 2021 (UTC)

Edge pieces on cake are often sought after because they hold more frosting, for cakes which are frosted while out of the pan. 06:37, 2 December 2021 (UTC)

I have an impression that Cueball is delighted by having only edge pieces, however some cakes edge pieces may be either sought for or avoided, depending on one's tastes. E.g. tarts have more crispy base cake content and less filling at the edges. One person may go for the filling, another for the crispy base. -- 09:50, 2 December 2021 (UTC)

So it seems the events in the comic happened on Apr 1., as the "last month" birthday could be either Feb 28. or 29. -- 09:50, 2 December 2021 (UTC)

Not necessarily. Remember, Emily can have her birthday whenever she wants, so the date this comic is set as is entirely arbitrary. 12:26, 2 December 2021 (UTC)

Are there any particular existing arctic international flights that could have been the one Emily was born on? -- 15:51, 2 December 2021 (UTC)

There are a few possibities (at least pre-COVID, and obviously we'd be looking historically in this case anyway) as might be shown here. There's two possible (but neither definite) International Datelines on the comic diagram, in case they help orient which from/to directions might have been diverted further in or out of their own kinks in the flightpath to coincide with 90°N. 16:21, 2 December 2021 (UTC)

Expanded copies of this comic have been appearing on other comics, so large that it fills the whole screen for me. Is anyone else having this problem? Sarah the Pie(yes, the food) (talk) 22:24, 2 December 2021 (UTC)

Someone (check the Recent Changes page, if you want) has been vandalising a lot of things. Currently I see a picture of an amphibious avian creature on this article's top (if I still need to revert it myself, I will do, but I've seen others have already been reverting other recent vandalism, so I may not need to by the time I've checked again). This very clever individual is obiviously mentally superior to us all(!) the way they can edit wiki pages seemingly at will... Impressive, eh? At some point I'm sure we'll get back to normlal, however boring that may be. 23:33, 2 December 2021 (UTC)

Not to be too pedantic but isn't rotation a FREQUENCY, not a SPEED? Skulker (talk) 03:19, 3 December 2021 (UTC)

Depends on the context (and scale). The convention is usually speed for rotation (surface(distance/time) when it's relevant, angular(revolutions/time) otherwise) to avoid conflicts with wave frequency (which is independent of speed). Also they can be freely converted, though converting to and from surface speed requires an additional radius term. The exception is, if comparing periodicity, sometimes frequency is used when it has special relevance (Ex: resonance) -- 02:59, 4 December 2021 (UTC)

Tempted to add a link in the Trivia section to the Wikipedia or Snopes pages on the SS Warrimoo, a ship that (reportedly) was on the intersection of the Equator and the International Date Line at the stroke of midnight on January 1, 1900, with a number of interesting implications that follow. There's no way to prove that it actually happened, but it's fun to imagine and is somewhat similar to the premise of the comic. --mezimm 14:33, 3 December 2021 (UTC)

What convinces me that it's a post-constructed yarn, rather than a legitimate account of a plausible event, is that the 1899-1900 'specialness' is (numerically aside) significant only from a more modern viewpoint. The dominant view at the alleged time of the incident, was the 1-rooted changeover between Centuries (1801 through to the end of 1900, then 1901-2000 to follow), and only changed as the more classical form of education/opinion phased out of common use. It was either later contrived from whole cloth as a tall-tale (if done at the time, it would have been given a 1900/1901 timestamp) or gradually embroidered with all the extra coincidental boundary-crossings (spatial and temporal) well after the actual inspirational seed incident in order to make a better anecdote/shaggy-dog-story.... 15:33, 9 December 2021 (UTC)
Okay... but it's fun to imagine... and is somewhat similar to the premise of the comic. And I'd say it's a good deal more plausible than the situation presented in the comic. --mezimm 16:30, 14 December 2021 (UTC)

Many airplanes actually have limitations written into their operating manuals that prohibit flying north of 89 deg. N or south of 89 deg. S, mostly just so that the navigation software doesn't have to deal with the singularity. 23:48, 3 December 2021 (UTC)

bloody lazy engineers! 12:19, 5 December 2021 (UTC)

Is it not possible that Emily's birth happened to occur at the same moment that the contract specified transfer of ownership? Additionally, is it not possible that the airplane took off from within UTC+13:00 or UTC+14:00 and that the moment of Emily's birth happened to occur in the brief one-or-two hour period in which it was March 1st at that airport, but February 28th in UTC-12:00? UTC-11:00 is inhabited, so it would be possible that ownership of an airplane that took off from within UTC+14:00 was transferred to a company based out of UTC-11:00 during the one-hour period that it was February 28th in UTC-11:00 and March 1st in UTC+14:00 and that, at that exact moment, it was passing over the North Pole. DL Draco Rex (talk)

Am I alone in thinking that babies don't get born instantaneously? I've never given birth myself but i'd always got the impression that it's a process and any attempt to pick a precise 'instant' is going to be somewhat arbitrary. This means that the plane will very probably have travelled through a variety of time zones any of which could be the 'real' time of birth. 05:29, 4 December 2021 (UTC)

Time of birth is an arbitrary decision made by the midwives filling out forms in a hospital. The more unlikely point about that is that she'd be able to correlate the precise position of the plane at the exact time listed. 12:37, 5 December 2021 (UTC)

Dickenson looks like a typo. Dickinson? 08:44, 4 December 2021 (UTC)

Isn't an "all edge pieces cake" just a plate of cupcakes lol? Zman350x (talk) 06:46, 5 December 2021 (UTC)

Only if you frosted all sides of it. 12:25, 5 December 2021 (UTC)
Alton Brown made a similar argument, but after experimenting, I strongly disagree. As with brownies, the cooking pattern is slightly different between having more edges and having a cupcake shape. In an edge piece, the edges and the corners are crisp while the center is gooey. Meanwhile, if cooked in a cupcake tin, while there might be more crispness, there is significantly less gooeyness. Cwallenpoole (talk) 14:23, 6 December 2021 (UTC)
If you cut the sheet into quarters or if the whole was round and cut with radial slices there won't be any center piece(s). And there are more, unusual cuts that could result in all edge pieces... 14:40, 6 December 2021 (UTC)
My take was that a normal cake was baked, frosted and cut (with both edge and center pieces), and only the edge pieces were delivered to Emily.
Only a cake baked in a fractal pan would be good enough for her!

Any commentary on the fact that the middle panel shows 25 time zones? Inca hoots (talk) 16:12, 9 December 2021 (UTC)

this comic has the same number as the carrier pigeon RFC, 2549. maybe related? 19:37, 31 March 2022 (UTC)Bumpf