Another Calendar / Time Thread.

[Keklas Rekobah]

First off, I have done a search through the General Traveller Discussion fora to see if this specific question has been addressed. I did not find any such instance; but if one exists, I apologize in advance for starting a new thread on an old topic. Note that I am assuming a value of 365.25 days of 86400 seconds each for a Mean Tropical Year for Terra. So my question is...

Is there any "slippage" between the Imperial and Terrestrial dating systems?

Let me explain...

IF:

a) The Imperial Year is defined as exactly 365 days.

b) The Terrestrial Year is defined as 365.25 days.

c) The Imperial and Terrestrial years have the same number of Terrestrial seconds (365.25 x 24 x 60 x 60 = 31,557,600)

THEN:

d) The Imperial second is approximately 1.000684 times longer than the Terrestrial second, making the Imperial day 86459.18 Terrestrial seconds long (e.g., an Imperial day is about 24 hours, 00 minutes, and 59.17808 Terrestrial seconds long).

e) Imperial and Terrestrial years have no "slippage" in determining their respective years (i.e., Imperial Year -4520 is Terrestrial Year 1 A.D., and Imperial Year 1000 is Terrestrial Year 5521 A.D.).

** HOWEVER **

IF:

f) The Imperial seconds and Terrestrial seconds are exactly the same length.

g) The Imperial Mean Tropical Year is defined as 365 days of 86400 seconds each (31,536,000 seconds).

h) The Terrestrial Mean Tropical Year is defined as 365.25 days of 86400 seconds each (31,557,600 seconds)

THEN:

i) The length of the Terrestrial year is about 1.000685 times the length of the Imperial year (e.g., 365.25 / 365).

j) Imperial and Terrestrial years have "slippage" in determining their respective years (i.e., Imperial Year -4520 is Terrestrial Year 1 A.D., and Imperial Year 1000 is Terrestrial Year 5524 or 5525 A.D.).

...

Q1) Which is more canonical?

Q2) Am I even using the correct reference years?

Q3) Is there even a canonical means of converting between Imperial and Terrestrial dating systems?

 

[mike wightman]

I just use the calendar in MT Imperial Encyclopedia to convert between earth dates and Imperial.

 

[aramis]

Note that the Earth year is 365.2422 days, not 365.25 days.
Which is why we skip a leap day once a century.

 

[ovka]

Which is why we skip a leap day once a century.

Actually, to be more exact, 3 times every 4 centuries. I had to do a lot of date logic programming during the Y2K conversion. 1600 and 2000 were leap years. 1700, 1800, and 1900 were not.

Sorry, I usually try not to pick nits. :nonono:

Cheers,

Baron Ovka

 

[robject]

Yes, theoretically there's slippage.

Theoretically, because the rules ignore it. Hey, maybe the Imperial day is different by just enough that the calendars stay in sync over the long run. Ha ha.

 

[coliver988]

Somewhere I remember reading that there is an official Imperial Calendar Compliance office which is really a cover to more clandestine pursuits. It gave them access to the bureaucracy on Imperial worlds.

Or was that just MTU?

 

[ShawnDriscoll]

Actually, to be more exact, 3 times every 4 centuries. I had to do a lot of date logic programming during the Y2K conversion. 1600 and 2000 were leap years. 1700, 1800, and 1900 were not.

Sorry, I usually try not to pick nits. :nonono:

Cheers,

Baron Ovka

Me, too. I was writing such code before the Y2K thing though. Centuries had to be divided by 400 to make the cut, if I remember. There was an article on the Imperial calendar that had corrections to keep things in sync. Maybe a Space Gamer issue.

 

[JimMarn]

Yes. Divide by 4 to be a leap year, but centuries ending in two zeros had to be divisible by 400 to be a leap year.

I had to do that in one of my first programming classes... Apple Fortran v1.0. I am very glad I didn't have to do that after i transferred to my 4-year university.

 

[Reban]

You lost me at point d) postulating Imperial and Terrestrial seconds of different relative length.

What reason could there be for such an odd departure?

Today we base the lenght of a second on atomic vibration:

Far better for timekeeping is the natural and exact "vibration" in an energized atom. The frequency of vibration (i.e., radiation) is very specific depending on the type of atom and how it is excited. Since 1967, the official definition of a second is 9,192,631,770 cycles of the radiation that gets an atom of cesium-133 to vibrate between two energy states. This length of a second was selected to correspond exactly to the length of the ephemeris second previously defined. Atomic clocks use such a frequency to measure seconds by counting cycles per second at that frequency. Radiation of this kind is one of the most stable and reproducible phenomena of nature. The current generation of atomic clocks is accurate to within one second in a few hundred million years.

Atomic clocks now set the length of a second and the time standard for the world

For a sci-fi setting it seems likely that atomic clocks would be standard*. I suppose aliens might define their time units with a different number of cycles that is meaningful to their time reference system, but a second is a second.

Its much simpler to assume that a second is a second and that SI units are in use.

This either means:

1). There is slippage that is not accounted for
2). There is slippage that is adjusted for
3). The Julian year of 365.25 days is lost to history.

Check my math but the Terran calendar would be out by a day for every four Imperial years that pass, and out by a year for every 1460 Imperial years that pass.

If you look at the history of the calendar on Terra, when a great enough divergence between the Gregorian and Julian calendars developed the date was arbitrarily adjusted to bring them back into sync.

So there may be slippage, but there also may have been an Emperor (or a clerk in the Office of Calendar Compliance) who ordered a "great Terran calendar reset" that occurs every 1460 years. A bit like the last year of confusion.


* There's an article out there on "Clocks in Traveller" that includes grav sheilded clocks that avoid gravity effects fron grav drives affecting the atomic clock. I think its on BARD.

[EDIT] Yes it was on BARD. might be useful to this discussion http://www.downport.com/bard/bard/gail/gail4015.html

 

[Enoki]

How would it work in different systems moving at various fractions of C? While this might amount to a few minutes a year, it adds up...

 

[mike wightman]

Time is relative, see general relativity.

Short version - atomic clocks calibrated to be exactly in sync will only remain so if they stay at the same height - move one of them to the top of a mountain or put it in orbit and you have to use general relativity to apply the correction. We have to do this today with out GPS satellites and the like.

Take the clock to a distant world and you are going to have the same issue, you will have to use general relativity to correct for differences in measured local time despite using the same atomic clocks.

 

[aramis]

How would it work in different systems moving at various fractions of C? While this might amount to a few minutes a year, it adds up...

Reference time would have to be based upon a specific world or star...

There is no way to keep time referentially identical across multiple systems moving at different speeds.

Local time can be synched by averaging the last X incoming from a neighbor, but even that is subject to issues with being wrong.

 

[kilemall]

Reference time would have to be based upon a specific world or star...

There is no way to keep time referentially identical across multiple systems moving at different speeds.

Local time can be synched by averaging the last X incoming from a neighbor, but even that is subject to issues with being wrong.

I would strongly consider using reference pulsars with set cycles as both a GPS satellite-like constellation for navigation and atomic timepiece.

The differing time delays and redshift on visual stars between different parts of the galaxy would also yield navigation information.

Heh, I just figured this would be a useful technique, but it's a really useful technology being developed NOW.

https://en.wikipedia.org/wiki/X-ray_pulsar-based_navigation

Found this related bad boy, using nanograv sensitive arrays from incoming pulsars to detect changes in gravitational fields. Perhaps a more tech-advanced version explains mass detectors, sort of an occlusion technique for gravity?

https://en.wikipedia.org/wiki/Pulsar_timing_array

 

[coliver988]

I would strongly consider using reference pulsars with set cycles as both a GPS satellite-like constellation for navigation and atomic timepiece.

The differing time delays and redshift on visual stars between different parts of the galaxy would also yield navigation information.

Heh, I just figured this would be a useful technique, but it's a really useful technology being developed NOW.

https://en.wikipedia.org/wiki/X-ray_pulsar-based_navigation

Found this related bad boy, using nanograv sensitive arrays from incoming pulsars to detect changes in gravitational fields. Perhaps a more tech-advanced version explains mass detectors, sort of an occlusion technique for gravity?

https://en.wikipedia.org/wiki/Pulsar_timing_array

This is where I would go if I wanted to get technical. None of my games really cared (some worlds had 400+ day years and had 2 calendars, local and Imperial).

It becomes particularly complicated when days are not 24 hours long: a 30 hour day is 1.25 Imperial days. So now the local day is split with 2 Imperial days. Or the reverse a 12 hour day has 1/2 Imperial days.

My feeling is that only the starports really care, and there is translation between local to Imperial where necessary.

 

[kilemall]

As for the OP, this wiki appears to state that the Solomani/Terran and Imperial calendars have drifter apart and are 'now' out of sync-

http://wiki.travellerrpg.com/Date_Conversion

If I were to be terribly concerned about keeping Terran time, I would add an extra Holiday date to the END of leap years, so 366-1105.

 

[Timerover51]

I anticipate that you will have two calendars. One for the planetary year and days, however long or short they are, and then the Imperial calendar which is maintained by the Star Port Authority.

The planetary populace is not going to worry about the Imperial calendar, they are going to want to know what season it is and when do they start planting stuff. Visitors will reset their watches to the local day, and proceed from there.

I have a planet that I am operating from where the day is 26 hours and 45 minutes long, so the expected work day is a nine-hour shift with an hour off for a meal to have three shifts work out. It does mean that visitors typically find themselves with extra sleeping time.

 

[Keklas Rekobah]

Note that the Earth year is 365.2422 days, not 365.25 days.
Which is why we skip a leap day once a century.

I use a value of 356.2421875, or 365 and 31/128 days of 86400 seconds each per Mean Tropical Year in most of my own calculations, instead of the 365.25 value given in canon; but I tried to simplify this thread for the sake of those who may not be so mathematically inclined.

 

[Keklas Rekobah]

As for the OP, this wiki appears to state that the Solomani/Terran and Imperial calendars have drifter apart and are 'now' out of sync-

http://wiki.travellerrpg.com/Date_Conversion

If I were to be terribly concerned about keeping Terran time, I would add an extra Holiday date to the END of leap years, so 366-1105.

Now THAT all makes sense!

Thank you.

 

[McPerth]

See my own assumptions for calendars in this thread. While Hans (god have him) refuted them, his own post is also quite interesting in this way.

 

[Keklas Rekobah]

Time is relative, see general relativity.

Short version - atomic clocks calibrated to be exactly in sync will only remain so if they stay at the same height - move one of them to the top of a mountain or put it in orbit and you have to use general relativity to apply the correction. We have to do this today with out GPS satellites and the like.

Take the clock to a distant world and you are going to have the same issue, you will have to use general relativity to correct for differences in measured local time despite using the same atomic clocks.

So, by syncing clock to an agreed-upon pulsar, both the Imperium and the Terries would have the same reference.

But would the Imperium base their second on a sub-multiple of 1,000,663,527,397 pulses while the Terries base theirs on a sub-multiple of 1,000,000,000,000 pulses from the same pulsar?