Help needed comparing planetary "calendars"

[sheepcountme]

Summary:: Writing a YA Space Opera series, but I'm lost on trying to create a formula for calculating "Earthbirth Days"

Short run down: Earth was no long hospitable to humans so we left to colonize a new planet, Nemesyne. People on Nemesyne still celebrate their "Earthbirth Days" and count their ages according to the traditional Earthen calendar. Nemesyne has 300 days a year (though I haven't gotten into what would constitute as minutes or hours - so far I've avoided these terms completely to stay consistent with my world building). So, one's "Earthbirth Day" would be a different Nemesynian date every time it came around. If you were a resident of Nemesyne, how would you know what date your next Earthbirth Day was going to be?

 

[Drakkith]

Assuming the length of a day on Nemesyne is identical to Earth it should be 1 year + ~65.25 days.

 

[phinds]

If you were a resident of Nemesyne, how would you know what date your next Earthbirth Day was going to be?

If you were a resident there you would likely have the equivalent of a smartphone that would just TELL you.

 

[Ibix]

You want to add 365 Earth days, or 366 every fourth time. Assuming a local day is the same length as an Earth day then, as Drakkith says, this is just one local year (300 days) plus 65 or 66 days.

If local days are a different length - say 0.9 Earth days (21 hours 36 minutes) - then 365 Earth days is 365/0.9=405+5/9 local days, which is one local year plus 105 and 5/9th days. You'd need to keep track of the fractions - so your first Earthbirth day would be after a year and 105 days, but you'd need to remember that 5/9ths and add it on next time. So your second Earthbirth day would be after another year and 105+5/9+5/9 days, which would be 106 days with 1/9th day to carry forward.

In either case the calculation is straightforward, but the book keeping gets messy. It's easy to write a spreadsheet to keep track, though. Or, depending on your tech level, have published tables someone calculates by hand (but you use a spreadsheet anyway).

(Or you can make it messier if you want - I mean, at this time where I am it's February 5th, but it's still the 4th in some parts of America...)

 

[PeterDonis]

Moderator's note: Thread moved to SF world building forum.

 

[sheepcountme]

If you were a resident there you would likely have the equivalent of a smartphone that would just TELL you.

Well, they do actually. It's a tablet called the smallvox. However, I still need this wonderful capability myself to keep things consistent in my story.

 

[sheepcountme]

You want to add 365 Earth days, or 366 every fourth time. Assuming a local day is the same length as an Earth day then, as Drakkith says, this is just one local year (300 days) plus 65 or 66 days.

If local days are a different length - say 0.9 Earth days (21 hours 36 minutes) - then 365 Earth days is 365/0.9=405+5/9 local days, which is one local year plus 105 and 5/9th days. You'd need to keep track of the fractions - so your first Earthbirth day would be after a year and 105 days, but you'd need to remember that 5/9ths and add it on next time. So your second Earthbirth day would be after another year and 105+5/9+5/9 days, which would be 106 days with 1/9th day to carry forward.

In either case the calculation is straightforward, but the book keeping gets messy. It's easy to write a spreadsheet to keep track, though. Or, depending on your tech level, have published tables someone calculates by hand (but you use a spreadsheet anyway).

(Or you can make it messier if you want - I mean, at this time where I am it's February 5th, but it's still the 4th in some parts of America...)

Spectacular explanation! Thank you! I'm pretty adept at creating spreadsheets so this will be a minor task.

 

[Algr]

Nemesyne has 300 days a year

Yes, this is actually ambiguous until you define how long a Nemesyne day is. If a Nemesyne day were 29.2 Earth hours long, then 300 of them would add up to a year that was the same length as Earth's year. Earthbirth Days would then happen on the same Nemesyne date every year! Of course that is not what you said you wanted.

Earthbirth Days would be an important factor describing childhood development. Right now we all agree what an "Eight year old" is and what can be expected from such a person. But the rotation of a planet around its star would have no effect on human development. If a Nemesyne year was half as long as an Earth year, the person described above would have seen 16 full turns of the seasons, but would still be a child, not a teenager.

 

[Melbourne Guy]

People on Nemesyne still celebrate their "Earthbirth Days" and count their ages according to the traditional Earthen calendar.

How many generations have been born on Nemesyne when the story is set? (And how did they get there? Arkship? or FTL?)

Natives tend to reject the traditions of their non-native parents. Plus, cultural aspects irrelevant to the society tend to be jettisoned for locally developed traditions. I can well imagine Nemesyne teenagers complaining, "Oh come on, who cares about Earth anyway, you made it inhospitable and we had to escape to this dump, so can't we just stop celebrating and all? It's not like it means anything here!"

If it's a YA novel, rebellion and creating tribal traditions and mores would be emotionally on point for the readership. Unless you're looking for the Earthborn celebrations to be a trigger for rebellion, @sheepcountme?

 

[Drakkith]

Natives tend to reject the traditions of their non-native parents. Plus, cultural aspects irrelevant to the society tend to be jettisoned for locally developed traditions.

Well, historically it's usually a mix of the two.

 

[Melbourne Guy]

Well, historically it's usually a mix of the two.

True, @Drakkith, but I'd still wonder whether a celebration so disconnected from local conditions such as Earthbirth Days and recording your age in Earth years would survive even a single generation.

We celebrate Christmas Down Under with lots of northern hemisphere imagery - snow, sleds, reindeer, etc. - even as our southern hemisphere day is more likely to be spent in shorts sitting by the pool than building snowmen and skating in the park. Such dissonance is minor compared to trying to align with a calendar for a planet I have no recollection of, emotional connection to, and for which I need an electronic calculator to keep track of the 'days'.

Obviously, there are many contrived scenarios in literature, but unless this is a major motivator of the narrative, it seems more annoying inconvenience than likely outcome of exoplanetary colonisation.