> That means that when the clock strikes midnight on New Year’s Eve, Earth hasn’t quite circled all the way back to its starting point.
Circling back to the starting point would be a sidereal year, which isn't what we want either.
What the calendar is trying to synchronize to is not the sidereal year, but the tropical year: the equinoxes and solstices should occur around the same date each year, and the seasons shouldn't shift relative to the calendar over the years. Because of the precession of the earth's axis, this tropical year is about 20 minutes shorter than the sidereal year.
The seasons are caused by the orientation of the Earth's tilted axis relative to the sun. E.g the north pole is tilted towards the sun during summer of the northern hemisphere, and away from the sun in winter.
Now imagine the Earth being magically held in place, instead of orbiting around the sun. This would almost stop the seasons from advancing, but not entirely. There would still be a slow 26000 year cycle of the seasons, because the Earth's axis precesses much like a spinning top. It's this effect that speeds up the cycle of the seasons by about 20 minutes each year. (1 year/26000 is about 20 minutes)
It's pretty random. It's mostly caused by gravitation from the sun and moon, and counteracted by the Earth's spin; faster spin would mean slower precession.
When you go from Casablanca to Detroit, when you arrive, you adjust to Detroit time (as well as weather, etc.) because this is the place your are in, and only take the pain to compute/represent yourself time in Singapore when you communicate with someone over there (instantly in that case).
When you travel by boat from Southampton to Auckland, during the travel, you mostly only care about the flow of time on the boat, where it is, regardless of the time in the departure & arrival places. You only expect to be in Auckland, around a certain local time.
Going from Earth to Mars, or from the solar system to an Aldebaran planet is slightly the same (but that the flow of time itself may be relative between the places you left/arrived at, and the place you are):
- you expect to be somewhere in the future in about a relative time to where you are (I'll be there in what I know/can represent myself to be X-earth-years);
- you will account for inevitable delays during travel, that might be significant at your scale, but not to others';
- when arrived there, you'll try adjust to the local time keeping method that makes sense to locals - if only because that's how you will interact with them about the flow of time.
You may get to compute what's the relative time on Earth, at the same instant, or when they will get your message. Just as everyone do today (and before) when communicating through slow (aka, human-borne) package & mail delivery.
We can consider having an atomic (or similar) clock that pulse at the same rate, on both Aldebaran & Earth. But:
1. would they be still in sync? experience seems to say no; do we know how we would be even in a position to check that remotely?
2. would it be relevant, relative to Aldebaran-time-keeping? (the atomic second as it is used on Earth is 1/86400th of a full Earth day; it may be wildly on a different planet)
Relativity says it’s impossible for two observers to agree on things like simultaneity, distance, duration, etc. Without reference to astronomical landmarks (observed within a given proximity of the solar system, at low speed) how could anyone agree on the meanings of time intervals?
I believe the cosmic microwave background provides a reasonably universal rest frame to anchor your definitions of time. It should at the very least be a lot less local than using the rest frame of a particular solar system.
And a hectosecond (which I assume is what a hectasec is) is just one minute and forty seconds... I hope he would be able to stay awake a little longer than that.
Somewhat related to this, back in 2004 the JPL team working on Spirit and Opportunity were given specially-designed wristwatches that matched the 24 hour and 39 minute day on Mars in order to better match the daily working schedule that Mars required.[0]
> The term sol is used by planetary scientists to refer to the duration of a solar day on Mars. The term was adopted during the Viking project in order to avoid confusion with an Earth day. By inference, Mars' "solar hour" is 1/24 of a sol, and a solar minute 1/60 of a solar hour.
I wish they would have picked another name. As a Spanish speaker, I can't stop my mind translating "sol" to "sun". I can already imagine hearing someone say, "how was your sun today?"
That may have actually been (slightly?) intentional. When talking about our Sun in the greater context of stars, I've often seen it referred to as "Sol". The best immediate example I have are games like Stellaris or Elite: Dangerous which refer to our home system as the "Sol System" and our star as "Sol", but I recall hearing it in non-sci-fi contexts as well.
I'm not really sure how the etymology works out on all of that, though.
If you call it something more verbose like <x>ian day, people are just gonna shorten it in conversation to "day" and then you end up with confusing ambiguities.
You have to know your mythology well to understand that.
Tyr was the Norse god of war, so equivalent to Mars.
Wotan was an old name for Odin, who started as the messenger of the gods, like Mercury. (The connection was clearer when Tacitus was comparing German and Roman mythologies than in current Norse myths.)
Thor was the god of thunder, like Jupiter.
Frey and Freya were god and goddess of fertility, so parallel Venus.
English already has the same names. Wednesday is Woden's day. Thursday is Thor's Day, Friday is Frigg's day. These are just English translations of the planets associated with the gods.
The names of the days of the week are fairly uniform on Earth. Monday (Moon-day) = lunes (spanish) = 月曜日 (japanese - getsuyoubi, moon day). Sunday = 日曜日 (sunday, or almost "sun sun"). These came through China and are very old names -- tying the seven objects you can see move against the background stars (ignoring Uranus if you know where to look) is an idea going back the the classical era.
> These came through China and are very old names -- tying the seven objects you can see move against the background stars (ignoring Uranus if you know where to look) is an idea going back the the classical era.
Well, the Japanese weekday names come to Japanese through China. They don't originate there; the fact that they occur in the same order as the Western days of the week strongly suggests that they didn't develop independently.
The native (old) Chinese system divides months into three roughly equal 旬 periods; seven-day weeks aren't part of it.
I assume there are people at NASA / SpaceX/ etc. in charge of writing custom MarsDate modules for various languages. Sounds horrible. I'm not even sure we've solved how to deal with dates on earth yet.
I'd be more interested to see if a more generalised PlanetDate module could be written. Perhaps outside of Earth we could do away with months and just stick to days (based on rotations, assuming the planet rotates) and years, with leap days added in between? And if the planet doesn't rotate, just count by hours and years (with hours having a logical separator at 10 or 100)?
“There may come a time — if you have cultural civilizations that are living in this environment and you want to preserve the seasonal significance of a particular date on the calendar — that you would likely introduce some sort of a leap system,”
It never occurred to me until reading this that the main reason we care about syncing our calendar to the seasons is mostly cultural.
We could easily just count days and have equal months and be done with it if we didn't care about certain days happening in the same season.
Saying that it's mostly cultural IMHO misses the point - having certain days happening in the same season is the whole point of having calendars; unlike the length of weeks and months (which are arbitrary and cultural) there are practical reasons to require an accurate metric for years that doesn't shift seasons around because that affects our agriculture.
For much of human history, farmers needed to know that (for example) this spring is later or earlier than usual, because that affects the length of the growing season they'll see - if they would just start planting solely based on the weather conditions, that's not the best way to go.
Nowadays we could just "directly" make weather predictions based on all kinds of factors, so today we could decouple calendar from seasons if we wanted to, but historically having a calendar that is (for example) two weeks off of traditional seasons would be a bad thing. Sure, you could just learn to adjust, but if you're adjusting anyway, why not adjust the calendar directly - since the vast majority of people were either farmers or derived their income from farming (i.e. landlords / aristocrats), the practical needs of the farming industry outweighed pretty much every other factor.
In fact, it was the Catholic church that officially declared the Gregorian calendar we use today. The motivation was to make sure Easter always fell on the same day.
Doesn't every planet? I'd be astonished if every planet completed a revolution in a perfect multiple of rotation time. Wouldn't it would have to be an engineered system if it did.
Or is that just tidal locking? I know the moon does something similar but there it seems like revolution time = rotation time, not perfect multiple.
> But there is one planet where the calendar would need zero finessing: Mercury. The small planet revolves exactly three times, or days, over the course of two years — allowing its calendar to naturally align every other year.
I would imagine that this is some form of resonance, like the tidal locking of the moon, but i can't explain it myself.
> In some cases where the orbit is eccentric and the tidal effect is relatively weak, the smaller body may end up in a so-called spin–orbit resonance, rather than being tidally locked. Here, the ratio of the rotation period of a body to its own orbital period is some simple fraction different from 1:1. A well known case is the rotation of Mercury, which is locked to its own orbit around the Sun in a 3:2 resonance.
Circling back to the starting point would be a sidereal year, which isn't what we want either.
What the calendar is trying to synchronize to is not the sidereal year, but the tropical year: the equinoxes and solstices should occur around the same date each year, and the seasons shouldn't shift relative to the calendar over the years. Because of the precession of the earth's axis, this tropical year is about 20 minutes shorter than the sidereal year.