Talk:Date Conversion

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Notes (2019)[edit]

Thank you for correcting previous errors, Thomas.

  • Please do not remove citations of any kind or add superfluous spacing to references or disciplinary action may be taken.
- Maksim-Smelchak (talk) 08:59, 22 June 2019 (EDT)

Notes (2007)[edit]

I just noticed, while editing the entry for Year -536, that the conversion between the Imperial and the Solomani calendars is faulty. -536 is equivalent to 3985 A.D., but the conversion routing makes it 3982 A.D. The Imperial calendar doesn't have leap years, so it and the Solomani calendar gets one day out of whack for every four years, or one year out of every 1460. I'm guessing that's where the discrepancy comes in.

I spent a lot of time on figuring out the dates in Sword Worlds, converting to Julian days, adding and subtracting, and converting back again. Though I won't gusrantee that I didn't make any mistakes, I don't think I did.

Anyway, I based my calculations on one of the few canonical dates where we have both the Imperial and the Solomani date. Based on it, I worked out that 001-1120 is equivalent to April 14, 5640 A.D. Of course I can't remember it now, but I'll track it down and post it.

The Template:Date uses the conversion given in the Date conversion article: (Year * 1.0006644) + 4518. According to the formula IY 1120 calculates to 5638. So both are off by about two years, I'd guess the +4518 should be +4520. If you can convert a few more known dates, and the fix makes the dates more correct, I'll fix the template. Tjoneslo 20:37, 28 April 2007 (UTC)

There are a number of different canonical Imperial dates with their equivalent Solomani dates. Unfortunately, they don't match up. There's nothing inherently wrong with any of them, except that if some of them are right, others can't be and vice versa. So when we were working on Sword Worlds I decided to pick one date as true and calculate everything else from that. It's hardly rocket science, but it is tricky. It's also the sort of thing that it's unlikely that "real" historians from the TU would get wrong, since presumably their computers are as capable of converting as ours are.
Anyway, the date I chose was 292-950 Imperial (13 March 5471 Terran), the date Margaret chose for decreeing the reintegration of the Solomani Sphere into the Imperium. The reason why I chose that date instead of, say, Year 0 is that it's one of the few canonical dates with the day as well as the year (In fact, although I think there are others, I can't remember any of them at the moment).
To work out other dates, you first take one of the Julian Day Converters available on the net, like and enter March 13, 5471, which tells us that it is Julian Day 3719372. However, because Julian Date Converters use the unrevised Gregorian Calendar, it thinks it is March 12 when the Solomani thinks it's March 13, so to get the real Julian Day, we have to subtract one. So 212-950 corresponds to JD 3719371. To get 001-1120, you add 154 days to 001-251 and add 169*365 = 61,685 for a total of 61,839. Add that to 3719371 to get 3781210. Enter that into the JD converter, and you find that 001-1120 corresponds to July 1, 5640 -- and not April 14, 5640 A.D. as I wrote in Sword Worlds!!!
I know I went over and over those calculations back then, so how could I possibly be 78 days off!?!
At this point I'm going to take a break, go home and check my notes (if I can find them which I doubt) and the draft of SW that we submitted to SJG. If someone would doublecheck my calculations, I'd be most grateful. I'm really bothered and bewildered by this turn of events.
Rancke 14:03, 30 April 2007 (UTC)

OK, I've had a look at my old files, and it's clear that however the mistake was made (and I'm still at a loss to understand how I could blunder like that) I'm the one that made it. I'm really, really bummed out by that...
But be that as it may, I still think the idea itself is correct. Chose one date to be correct and calculate from that. Which, come to think of it, is what you're doing right now. The only difference is that you're using Year 0 equals 4518 A.D. as the baseline date whereas I suggest using 292-950 equals 13 March, 5471 A.D. as being more precise (and equally canonical (not more canonical, just equally)). Rancke 14:34, 1 May 2007 (UTC)

I've just identified the biggest part of the mistake. Somehow I got 292-950 turned into 212-950 halfway thorugh the example above, which accounts for 80 of the 78-day discrepancy. The excess two days are obviously down to the one-day difference between the Gregorian and the Revised Gregorian. Either I added it up the wrong way back then or I added it up wrong when I was working out the example above. I'm going to look into that now, but I just thought I'd dash off this message to update you. Also, I'd like to repeat my plea that someone double-check my calculations. Rancke 14:44, 1 May 2007 (UTC)

OK, I've calmed down and am ready to try again (Also, I've done a smidgin of research about canonical dates).
When it's 28 Feb 4000, a Julian Day Converter thinks it's 28 Feb 4000 (JD 3182087.5).
There was no 29 Feb 4000, but JDCs think there was.
When it's 1 March 4000, a JDC thinks it's 29 Feb 4000. (JD 3182088.5)
When it's 2 March 4000, a JDC thinks it's 1 March 4000. (JD 3182089.5)
When it's 3 March 4000, a JDC thinks it's 2 March 4000. (JD 3182090.5)
When I enter JD 3182090.5 into the converter, I get 2 March 4000, so to get the right date, I have to add 1.
When I enter 2 March 4000 into the converter, I get 3182090.5, so to get the right JD, I have to subtract 1.
When I enter 13 March 5471 I get 3719372.5. To get the right JD, I have to subtract 1 = 3719371.5.
292-950 corresponds to JD 3719371.5.
001-1120 corresponds to 3719371.5+170*365-291 = 3781130.5.
3781130.5 converts to 13 April 5640, but to get the right date I have to add 1 = 14 April 5640. YAH!
So I did get it right in Sword Worlds. That's a great relief.
Now let's talk about what Solomani year Year 0 Imperial corresponds to.
Holiday, Year 0 is 950*365+291 = 347041 days before 292-950, so it's JD 3372330.5.
JD 3372330.5 converts to 10 January 4521 == 11 january 4521.
So if we accept the date for Margaret issuing her decree, Year 0 = 4521 A.D.
What does other sources say? Well, about half of them (IE, TNE, and S&A) say 4518. But the earliest I can find (Library Data (A-M), p. 10) says 4521, and other sources says 4519 (Gateway), 4524 (GT), and 4526 (another part of AM6). And, of course, Sword Worlds' says 4521 ;-).
So I submit that there is a good argument for going with 292-950 = 13 March 5471. To get that, you should change the formula to (Year * 1.0006644) + 4521.0301. (I think ;-).
Rancke 11:05, 6 May 2007 (UTC)

So can this be expressed as an Excel forumla for us date-dunces? Gruffty 18:53, 6 May 2007 (UTC)

I tried plugging the two formulae into Excel as they were; I couldn't get them to agree dates. Gruffty 19:46, 6 May 2007 (UTC)

I fixed the Template: Date to your formula above. Keep in mind the date template rounds to the nearest year according to whatever default rounding formula the PHP math library uses. Therefore the Solomani year may be off by as much as a year according to the template. If you find the date template year off by more than that (i.e. an acceptable margin) we can look at it again. Tjoneslo 00:28, 7 May 2007 (UTC)

Problem: CT:AM6 (p. 30) specifically states that 001-0 is 19 January 4521, not 11 january 4521. Gruffty 15:23, 7 May 2007 (UTC)

Ach! So it does. I knew there were other canonical references with both dates. I'm not surprised that they don't agree with each other either >>Sigh<<. Note that this is the very same book that has the date for Margaret II's edict (on p. 11). BTW, have you checked if my calculation of 11 Jan is correct?
The problem remains basically the same. Several dates that doesn't match, so we have to pick one over the other. If I had remembered about this one back when I was working on Sword Worlds, I'd probably have chosen 001-0 = 19 Jan 4521 over 292-950 = 13 March 5471 (at least the year matches). But I didn't, so the date in Sword Worlds matches the second and not the first. That's really the only reason I suggest sticking to that, but I think it's a pretty good reason. Rancke 16:05, 7 May 2007 (UTC)

Also, I can't seem to find that second reference to IY 0 being later than 4521 - any suggestions for a page number? Gruffty 15:53, 7 May 2007 (UTC)

What reference are you referring to? Rancke 16:05, 7 May 2007 (UTC)
Um, I got it. It's on p. 5 of AM6 where the First Interstellar War is said to begin in 2118 A.D. and in -2408. 2118+2408 = 4526.

AD Dates for Historical Periods[edit]

From the T4 Core Rule book, p 8:

  • Vilani Era: 4700 BC - 2300 AD
  • Terran Confederation: 2100 AD - 2300 AD
  • Rule of Man: 2300 AD - 2750 AD
  • Long Night: 2750 AD - 4550 AD
  • Third Imperium: 4521 AD - 5637 AD
  • Aslan Border Wars: 3400 AD - 4900 AD
  • Vargr Campaigns: 4700 AD - 4900 AD
  • Barracks Emperors: 5100 AD - 5140 AD
  • Solomani Expansion: 5121 AD - 6500 AD
  • Rebellion: 5367 AD (no end date given)

No entry for TNE/Recovery/4th Imperium. HTH Gruffty 20:16, 10 May 2007 (UTC)

This link: might be useful. It shows 13 March 5471 as a Sunday. Gruffty 21:25, 10 May 2007 (UTC)

That calender does not work for Feb 2900 or 3000 (or presumably beyond) so the proposed 4000 year rule is likely not correct... Dcorrin 21:54, 10 May 2007 (UTC)

<Confused...> The calendar in the link I posted (above) does work beyond the year 3000. I'm working out the current days and dates (i.e. Mon, Tue, Wed, etc and the months) for IY 0 with it as we speak. 001-0 = 19 January 4521 AD = a Saturday. <Still confused.....> Gruffty 22:45, 10 May 2007 (UTC)

The calender didn't work for Feb 2900 (as it showed that it had 29 days, when it should have 28) I didn't draw any conclusions about the rest, but I would think that April would be wrong. Perhaps it is just those xx00 years. Dcorrin 17:15, 11 May 2007 (UTC)

Here's a list of leap years from now until 6796 AD:

The list is wrong. The current rule is 'Every year divisible by four, unless it is also divisible by 100, unless it's also divisible by 400'. So 3600 will be a leap year, but 3700, 3800, and 3900 won't be. If this scheme is not changed, 4000 will be a leap year. However, there's a very small discrepancy that is not accounted for currently. Making years that are divisible by 4000 not-leap years would increase the accuracy a tiny bit. Some people think this modification will be introduced some day, others think it won't. Someone (I think it was Jon Zeigler, but I won't swear to it) once told me that Marc Miller had told him (JZ) that he (MM) thought the change would be introduced. Not the most impressive of evidence, but nowhere in canon does it say that it won't be, so I was free to chose either way. When I wrote my part of Sword Worlds, I established that it had, if fact happened). Rancke 12:54, 11 May 2007 (UTC)

Here's my IY 0/4521 AD calendar: Gruffty 23:42, 10 May 2007 (UTC)

If it's based on the assumption that all years that are divisible by 4 are leap years, then it's incorrect. If it's based on the assumption that the current rule remains in effect and that 4000 A.D. is a leap year, then it is wrong for Traveller universes. Rancke 12:54, 11 May 2007 (UTC)

Bah, bah, and bah again :( That leap year rule - is that something that applies to the RW, or just the OTU? Gruffty 07:15, 12 May 2007(UTC)

OK, so I did some research and foudn that the leap year rules are RW. And in doing so, I came across this perpetual 10,000 year calendar! It's a little tricky to use, but once you get the hang of it it's not too bad. Gruffty 09:15, 13 May 2007 (UTC)

OK, so looking for 19 January 4521: 45 cross referenced with 21 = D; 19 cross referenced with January = L; D cross referenced with L = Sunday. 001-0 = Sunday 19 January 4521. I was a day out ;) Gruffty 09:19, 13 May 2007 (UTC)

K'kree date conversion (2008)[edit]

According to AM2 (K'kree) the K'kree calendar should start on -8175. However if you back calculate the 1110 date (7713), it figures a start date of -8145. If you look in the Imperial Encyclopedia (p6,7) the conversion for the 1110 and 0 dates comes to -8145. If you calculate the start date from some of the other dates on that table, the K'kree calendar start year is something different. GURPS Traveller: Alien Races 2 has no explicit date conversion for K'kree <=> Imperial dates. so we use the -8145 date. Tjoneslo 04:59, 1 September 2008 (UTC)