Manticoran calendar wrong?

Let me preface this by saying that: 1) I've been trying to develop a comprehensive timeline for the Honorverse for a while now, and 2) I'm probably more anal about it than I should be

I recently obtained a copy of the RMN Jayne's Intelligence Review. Since it has Manticoran dates for Honor's pre-war service record, I thought: "Hey, I can convert these to Gregorian dates and add some new entries." Easy, right? After all, OBS says:

The official year of the Kingdom is 673 days long, with a leap year every third year. It is divided into 18 months, 11 of 37 days and 7 of 38, alternating for the first 6 and last 8 months, named (simply, if rather unimaginatively) First Month, Second Month, Third Month, etc.

Thus, Honor Harrington’s orders to Fearless, dated Fourth 25, 280 A.L. (using Official Manticoran Reckoning, or the Manticore planetary calendar), were also written on March 3, 1900 P.D. (Standard Reckoning)

So I decided to check on the date given for Honor's birthday, Ninth 22, 256 A.L. - which should correspond to October 1, 1859 P.D. - by calculating backward from her Fearless orders. Only it didn't - Ninth 22, 256 actually corresponds to May 7, 1856.

OK, I thought, so is the mistake in Jayne's dating or in the calendar design? To check, I decided to calculate forward from our other known date. First 1, 1 A.L. is stated to be March 21, 1416 P.D., so does adding 280 years of 673 days (plus almost four full M-months and 93 leap days) get you to March 3, 1900?

Nope. Instead you get December 2, 1930.

So it would seem that 673 days is a bit longer than a Manticoran year should be. Funnily enough, House of Steel lists Manticore's orbital period at 629.83 T-days instead of 673. I'm tempted to try this instead, but I'm stymied by the breakdown of the months and days per month, which equals 673.

Does anyone have any ideas to try to reconcile this? Thanks.

Yes, I'm pretty sure the calendar as described in the early text was broken. I noticed this ten years ago when I tried to reconcile the calendar myself. There's a couple other discrepancies, if I recall correctly (it's been a long time). I think one was that calcuting backwards from some text, the Post Diaspora calendar appears to start in Year 0, not Year 1 as described in the text. But I haven't gone back to those calculations in a long time; I'd have to derive all the work again.

Our current era calendar never had a year 0. Which is why the year 2000 was the last year of the twentieth century not the first of the twenty first. That was January 1 2001.

Cluttered Mind wrote:Let me preface this by saying that: 1) I've been trying to develop a comprehensive timeline for the Honorverse for a while now, and 2) I'm probably more anal about it than I should be

I recently obtained a copy of the RMN Jayne's Intelligence Review. Since it has Manticoran dates for Honor's pre-war service record, I thought: "Hey, I can convert these to Gregorian dates and add some new entries." Easy, right? After all, OBS says:

The official year of the Kingdom is 673 days long, with a leap year every third year. It is divided into 18 months, 11 of 37 days and 7 of 38, alternating for the first 6 and last 8 months, named (simply, if rather unimaginatively) First Month, Second Month, Third Month, etc.

Thus, Honor Harrington’s orders to Fearless, dated Fourth 25, 280 A.L. (using Official Manticoran Reckoning, or the Manticore planetary calendar), were also written on March 3, 1900 P.D. (Standard Reckoning)

So I decided to check on the date given for Honor's birthday, Ninth 22, 256 A.L. - which should correspond to October 1, 1859 P.D. - by calculating backward from her Fearless orders. Only it didn't - Ninth 22, 256 actually corresponds to May 7, 1856.

OK, I thought, so is the mistake in Jayne's dating or in the calendar design? To check, I decided to calculate forward from our other known date. First 1, 1 A.L. is stated to be March 21, 1416 P.D., so does adding 280 years of 673 days (plus almost four full M-months and 93 leap days) get you to March 3, 1900?

Nope. Instead you get December 2, 1930.

So it would seem that 673 days is a bit longer than a Manticoran year should be. Funnily enough, House of Steel lists Manticore's orbital period at 629.83 T-days instead of 673. I'm tempted to try this instead, but I'm stymied by the breakdown of the months and days per month, which equals 673.

Does anyone have any ideas to try to reconcile this? Thanks.

Did you take into account that a Manticoran day in only (I think something like) twenty two and some change hours?

crewdude48 wrote:Did you take into account that a Manticoran day in only (I think something like) twenty two and some change hours?

Twenty--two hours Twenty-seven minutes, IIRC.

crewdude48 wrote:Did you take into account that a Manticoran day in only (I think something like) twenty two and some change hours?

You know, at first read, I thought OBS had specified 673 T-days, but looking back through the Appendix I don't believe it actually says that at all. Using that figure, a year of 673 M-days equals 629.53 T-days, which is 0.3 days off the orbital period in House of Steel. Let me recalculate using that and see what happens. Thanks for pointing out what perhaps should have been obvious.

Cluttered Mind wrote:

crewdude48 wrote:Did you take into account that a Manticoran day in only (I think something like) twenty two and some change hours?

You know, at first read, I thought OBS had specified 673 T-days, but looking back through the Appendix I don't believe it actually says that at all. Using that figure, a year of 673 M-days equals 629.53 T-days, which is 0.3 days off the orbital period in House of Steel. Let me recalculate using that and see what happens. Thanks for pointing out what perhaps should have been obvious.

OK, I've finished the first part of the check - going backward to Honor's birthday. Ninth 22, 256 A.L. is still wrong, but it's much closer now - April 8, 1859 P.D. That said, if you instead use Fourteenth 22, 256, that does (depending on where you count the fractional day) correspond to either September 30 or October 1, 1859.