1825: 7 Eleven

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7 Eleven
Really, the only honest 24-hour stores are the ones in places like Arizona and Hawaii, and many of them are still wrong in certain years.
Title text: Really, the only honest 24-hour stores are the ones in places like Arizona and Hawaii, and many of them are still wrong in certain years.

Explanation[edit]

This comic pokes fun at the idiosyncrasies of time keeping. Since units of time are intimately tied to a planet's rotation, and planets rotate at different rates, time keeping doesn't always follow a simple pattern.

Many stores advertise being open 24/7, which means that they're open all day, every day. Many locations of the convenience store chain 7-Eleven are now "open 24 hours", again meaning they are always open (despite historically being open only from 7 AM to 11 PM local time, hence its name).

The main joke in the comic refers to the fact that a day on Mars (the time it takes for Mars to make a full rotation on its own axis) is about 24 hours and 37 minutes. If a 7-11 store is open for literally 24 hours per Mars day, then it would actually be closed for around 37 minutes each day. NASA, for its Mars missions, uses a "Mars-hour" that is one twenty-fourth of a Martian day; had the sign implicitly referred to 24 Mars-hours then the store would be open for the entire Mars day.

The duration for the Martian day used by Randall is the Martian sidereal day (how long it takes the non-Sun stars to get to the same position in the sky) of 24 hours, 37 minutes, and 22.663 seconds. However, Mars exploration missions use the Martian solar day (how long it takes the Sun to get to the same position in the sky) or sol of 24 hours, 39 minutes, and 35.244 seconds. Thus in practice, the 7-11 store would be closed for 39 minutes daily instead of 37 minutes. Likewise, Earth time usually refers to solar days; a typical (mean) sidereal Earth day is 23 hours, 56 minutes, 4.0916 seconds long.

The first part of the title text refers to daylight saving time (DST), where clocks are changed on predefined days of the year in order to maximize use of available sunlight. In the United States, most places set clocks forward by one hour on the second Sunday of March, resulting in a 23-hour day, and back again on the first Sunday of November, resulting in a 25-hour day. Thus technically, even a 7-11 in the US would not truly be open "24 hours" every day. Arizona and Hawaii are called out as exceptions because they do not observe daylight saving time (except on the Navajo reservation in Arizona). Randall has made fun of DST several times before, and once again he shows his disdain for DST by saying that in the U.S., only 24-hour stores within the two states not using DST are honest. This comic came out over a month after DST began in the US.

The second part of the title text refers to leap seconds, which may be added or subtracted to the end of June or December in order to synchronize time with Earth's actual rotation. Months with a leap second will see its last day being one second longer than 24 hours. Since leap seconds apply to all Earth-based clocks, any store on Earth would not technically be open for exactly 24 hours on such days. Leap seconds have been referred to before in the title text of 1514: PermaCal.

Transcript[edit]

[A person in a spacesuit is trying in vain to open the door to a convenience store, rattling the handle. Behind him stands a tall post with a big 7-eleven logo at the top and the opening hours on a bar below the logo.]
Sign: 7-Eleven
Bar: Open 24 hours
Door: Rattle rattle
[Caption below the panel:]
I'm glad they finally opened a 7-Eleven here on Mars, but it's annoying how it closes for 37 minutes every day.


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Discussion

I don't think the title-text references leap seconds, as it says that "many" are wrong, not "all". It seems more likely it refers to stores that claim to be open 365 days per year, and are hence wrong in leap years. 141.101.105.42 20:12, 17 April 2017 (UTC)

I agree that it would be closed for 39 (and a bit) minutes a day if it was open for exactly 24 hours. I think Randall made a mistake. 198.41.238.40 21:30, 17 April 2017 (UTC)

The parts in the description that talk about mixing "Earth and Mars time units" and "Mars-hours" don't make sense; I'm pretty sure there's no such thing as a Mars-hour. Despite the classical definition of an hour (which has since been replaced), an hour is defined as a number of seconds, and seconds are an SI unit based on the characteristics of Caesium-133 atoms...NOT defined as being a fixed fraction of a day. Even the unit "day" is often used to refer to a fixed unit of time nowadays (defined by the SI to be 86 400 s)...I believe this is one of the reasons why the solar day on Mars is referred to as a "sol" instead of a "day". 172.68.133.192 22:15, 17 April 2017 (UTC)

Nitpicking a bit, but the day is usually only 86400 seconds long (see 1481).
That's what I meant to say, SI defines it to be 86 400 s; I have no idea why I typed 86 401 s. It is fixed now.162.158.79.5 15:39, 18 April 2017 (UTC)
NASA's Mars Mission do divide the "sol" into 24 "Hours". I thought about adding this as a clarification the the Mars-Hours but that made the sentence somewhat unwieldy.141.101.107.216 09:27, 18 April 2017 (UTC)

Fun fact that might be interesting to add to the note about Arizona and DST. As stated already, the Navajo reservation observes DST, since it extends into Utah and New Mexico. However, the Hopi reservation, which is entirely enclosed by the Navajo reservation, does NOT follow DST. So in the one state in the Mountain Time Zone that does not observe DST, there is a region that follows DST, and inside that is another region that does not follow DST. 162.158.79.185 01:28, 18 April 2017 (UTC)

And looking at a DST map of Arizona, it appears there is at least one small area contained within that inner-most non-observing region that does observe DST... 162.158.69.63 08:11, 18 April 2017 (UTC)
Yes, it is a smaller Navajo area fully contained within the Hopi reservation, which is fully contained within the Navajo reservation, which is mostly contained within Arizona. 198.41.238.40 02:19, 21 April 2017 (UTC)
Up through 2006, some of Indiana didn't observe DST. That really screwed with my college career, being from Virginia. Some of the time I'm on DST, others I'm not.

Another fun fact: Warning: can't unsee. Randall's representation of the 7-11 logo is inaccurate, as the 'n' in the real logo is always lowercase. 162.158.255.22 00:29, 25 April 2017 (UTC)