Go to this comic explanation
|| This explanation may be incomplete or incorrect: Created by FRINGE FRUITCAKE – Please change this comment when editing this page. Do NOT delete this tag too soon.|
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. However, since the concept of time zones is thus irrelevant, researchers in the Arctic at or near the North Pole use Coordinated Universal Time as the local time standard by convention. 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 travelling 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.
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 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.
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 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.
Hairbun was last named "Emily" in 788: The Carriage. More specifically, that version of Hairbun represented Emily Dickenson, a real, historical person who had no such issues regarding her birthday.
- [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, anyways?
- 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.
Don't be a jerk.
There are a lot of comics that don't have set-in-stone explanations; feel free to put multiple interpretations in the wiki page for each comic.
If you want to talk about a specific comic, use its discussion page.
Please only submit material directly related to (and helping everyone better understand) xkcd... and of course only submit material that can legally be posted (and freely edited). Off-topic or other inappropriate content is subject to removal or modification at admin discretion, and users who repeatedly post such content will be blocked.