A Conversation for A Chronology of Time

A few snags

Post 1

Cheerful Dragon

Nice article, but I came across a few problems.

1) Leap years do not occur every 4 years. Centuries are divisible by 4, but are not always leap years. Centuries are only leap years if they are divisible by 400. Thus A.D. 1900 wasn't a leap year but A.D. 2000 was.
2) The months (and, indeed the year lengths) used are those used by the Christian (i.e., Western) world. Muslims and Jews, to name just two, have different systems. Perhaps this article should have been called 'A Chronology of Western Time'.
3) Seasons don't start on specific dates. The dates given are the dates of equinoxes and solstices. I'm not even sure the dates given are accurate. My calendar gives the Autumnal Equinox (Northern Hemisphere) as September 23, and the Winter Solstice as December 22.
4) Christ was NOT born in A.D. 0 (or 0 A.D., as the author puts it). When the dates after his birth were calculated, the monk involved had no knowledge of Arabian mathematics, and hence no concept of the number 0. Consequently, the first year A.D. was 1, not 0. This has caused a lot of aggravation for people who are convinced (rightly, IMHO) that the new millennium was celebrated in the wrong year.
5) Stonehenge is unlikely to have been a calendar, except in the loosest sense.


A few snags

Post 2

Munchkin

I believe the change from Julian to Gregorian calendars was to accomodate this no-leap-year-on-a-century thing. As to the Muslim calendar, it is 11 days shorter than the Gregorian one. Hence, although it is 1420 A.H. in Saudi Arabia, it has not been 1420 years A.D. (Gregorian, Julian, what have you) in the West since Mohammed went to Medinah.

Randomly, I did hear somewhere (so it may not be true) that Caesar Augustus had the Month of August named after him as it was the month that Cleopatra died, and he wished to remember her. So, what was it called before that?


A few snags

Post 3

Peet (the Pedantic Punctuation Policeman, Muse of Lateral Programming Ideas, Eggcups-Spurtle-and-Spoonswinner, BBC Cheese Namer & Zaphodista)

There's also no mention of the (extremely rare) double-leap year, with a 30-day February. I was hoping to finaly find out the rules for that one!

And, not even all Western systems follow this calender - since when did you hear of a Jewish date calculated from the birth of Christ?

To quote from "The Phenomenon book of Calenders", (which just happened to be lying 3 feet from my computer...smiley - winkeye) - "The Jewish calendar is luni-solar with 12 lunar months in some years and 13 months in others. By adding an extra month every third year or so, the calendar keeps New Year (Rosh Hashana) within the month of September..."

In fact, this reference differentiates between the Gregorian year and:

* Masonic Year
* Muslim Year
* Jewish Year
* Hindu Year
* Julian Year
* Byzantine Year
* Japanese Year
* Nabonassar Year
* Diocletian Year
* Indian Saka
* Grecian (Seleucidae)

The two factors stopping me copying the whole set into an entry are (1) laziness on my part, and (2) copyright. It still doesn't give the rule for the double-leap year, though, so if you want to make the entry into a complete chronology of Gregorian time, then that might be a productive line of research... smiley - winkeye


A few snags

Post 4

Spiritual Warrior

A response to some of these points:

1) I'll grant you - the figure given as 365.256 should be 365.242 (from Britannica).
2) It *is* stated that the calendar figures are Western.
3) This is an interesting one - Britannica nicely contradicts itself on this, but firstly I quote, 'The seasons--winter, spring, summer, and autumn--are commonly regarded in the Northern Hemisphere as beginning on the winter solstice...' etc.

Then in separate entries:
a) winter solstice, December 22 or 23; the vernal equinox, March 20 or 21; the summer solstice, June 21 or 22; and the autumnal equinox, September 22 or 23,
b)The vernal equinox,..., occurs about March 21, the autumnal equinox falls about September 23, ...
c) In the Northern Hemisphere the summer solstice occurs on June 21 or 22 and the winter solstice on December 21 or 22.

About all that can be said for certain is that the solstices fall on the longest (shortest) day, the equinoxes when day and night are equal, and that the seasons can be thought of as starting on these days.

5) Stonehenge is thought by many to be able to predict eclipses, and certain things occur on solstices and equinoxes, and has for these reasons been called a 'calendar' by many, even though it is not a calendar in the strictest sense. Can't see any harm in leaving the entry as is w.r.t. this point.


A few snags

Post 5

Peet (the Pedantic Punctuation Policeman, Muse of Lateral Programming Ideas, Eggcups-Spurtle-and-Spoonswinner, BBC Cheese Namer & Zaphodista)

I just found a reference to your "August" question...

Augustus Ceasar renamed the month "Sextilis" in 8 B.C. in his own honour, then stole a day from February and added it to the newly-named August, so that "his" month wouldn't have a lesser stature than that of Julius Ceasar, July. (Which was originally named Quintillus until 44 B.C.)


A few snags

Post 6

Giraffe

Things I have picked up (can't guarantee accuracy though)

The concept of measuring dates from an absolute point (eg AD etc) is relatively recent. Many civilisations stuck to the "Year X of the reign of King/Queen Y" approach for a long time. In fact the notion of AD was only popularised in the 7th or 8th century AD, and with a slightly incorrect notion of when year 1 should have been (since various biblical references require the Birth of Christ to be in approximately 4 BC).

The other interesting thing is that our 60 minutes and 60 seconds approach comes from the base 60 calculations of the Babylonians, and its one of the few examples of universally accepted non base 10 stuff left (if you ignore the few bizarre bits of imperial measurement left).


Two apologies

Post 7

Peet (the Pedantic Punctuation Policeman, Muse of Lateral Programming Ideas, Eggcups-Spurtle-and-Spoonswinner, BBC Cheese Namer & Zaphodista)

First, sorry - I missed the reference to the Jewish calendar in the preamble to the article.

Second - I really can spell "Caesar" - I just managed to typo it the same way twice! smiley - tongueout


Two apologies

Post 8

Phil

A year can be described as having both 365.242 and 365.256 days (and even 365.259) depending on your deffinition of the year.
The tropical year - the time between the spring equinoxes is 365.242.
The sidreal year - the time between the earth returning to a point relative to fixed stars is 365.256.


Two apologies

Post 9

The Cow

The important one is the seasonal one. This fraction explains the 4/not 100/400 rule, averaging at 365.2425 instead of .242 (your figure) This gives an max inaccuracy of one part in 300,000; or 1 day a millennium too much. (I think... it could be much less)
So a DOUBLE leap year shouldn't happen... unless it was to realign with a better measurement of when the spring equinox was.


Two apologies

Post 10

Peet (the Pedantic Punctuation Policeman, Muse of Lateral Programming Ideas, Eggcups-Spurtle-and-Spoonswinner, BBC Cheese Namer & Zaphodista)

But if the *physical* year is .0005 of a day longer than the *logical* year, then surely the logical year needs to periodically add a day to stay in step, hence the "double leap year"...?


Daylight Savings

Post 11

dElaphant (and Zeppo his dog (and Gummo, Zeppos dog)) - Left my apostrophes at the BBC

The entry states "When summer starts you set your clock one hour back, and when the winter sets in you set your clock one hour ahead...", but the rule I usually remember is "Spring ahead, Fall behind."

So the statement is wrong on two counts - the time change takes place in mid-Spring and mid-Fall, not the start of Summer/Winter/on the equinox, and the clock is moved *back* an hour in the Fall, and *ahead* one hour in the Spring. You've gotten it backwards. Also "Daylight Savings Time" only refers to the time when the clock is ahead one hour (late Spring through early Fall). The rest of the year is standard time. It is not mandatory in the US and a few places do not use it.

I'd like to know when the terms "CE" and "BCE" came in to use (replacing for some people the terms "AD" and "BC"). That's "Common Era" and "Before Common Era" I think (and common to whom?), whereas the older terms are "Anno Domini" and "Before Christ."


A few snags

Post 12

Almighty Rob - mourning the old h2g2

Christ was not born in AD 1, either.
The calendar was based on an incorrect calculation of the year of his birth. The accepted date based on modern scholarship is 5 BC.


A few snags

Post 13

Peet (the Pedantic Punctuation Policeman, Muse of Lateral Programming Ideas, Eggcups-Spurtle-and-Spoonswinner, BBC Cheese Namer & Zaphodista)

Or possibly 4 B.C., as mentioned earlier... (Post #6)


A few snags

Post 14

manolan


Well, the Julian calendar was quite a bit more complex than the Gregorian one, if I remember, as there were leap days that weren't part of any month. Also worth mentioning that in the year it was implemented in Britain, there were only about 20 days in September because so many days had to be missed out. Also, it was not implemented in the same year in each country.

You're absolutely right about the reason for Augustus choosing that month. It was more normal to choose the month of your birth, but he chose to remember Cleopatra's death. That was on TV recently, so it MUST be true.

Also, this article could do with some reference to UTC and the atomic clock.


Daylight Savings

Post 15

Cheerful Dragon

I always remember 'March forward, Fall back'. When the change is made depends on where you are. In Britain it is always the last weekend in March and the last weekend in September, which makes it almost the 'beginning of Spring' and 'beginning of Autumn', but not quite. Maybe the author is British and just got her forward and back mixed up.

I agree that 'Daylight Saving' is the time between the clock changes in March and September, but in Britain the technical term is 'British Summer Time' or BST.

I believe that the clocks also go forward and back in Europe, because Britain is always an hour behind, which we wouldn't be if their clocks didn't change too.


Daylight Savings

Post 16

The Cow

Logical year > Physical, therefore not double leap year.
CE/BCE (synonymous with BC/AD) is just a way of keeping non-christians who dislike the idea of using another religions 'gods' name in the year.

And it's common to everyone (ie: in common use) ... I suppose even in Israel they think it's 2000... (despite the fact the religious year is in the four thousands)


Daylight Savings

Post 17

Peet (the Pedantic Punctuation Policeman, Muse of Lateral Programming Ideas, Eggcups-Spurtle-and-Spoonswinner, BBC Cheese Namer & Zaphodista)

Sorry, TC, - I misread your previous post. I'm still certain I've seen a reference to an arcane rule for a "double leap year" which originated in the 1970s, after the use of atomic clocks to improve on the accuracy of measurement of the Earth's rotation. It was probably in a "Tomorrow's World" paperback of the era which, sadly, I no longer have... smiley - sadface


Daylight Savings

Post 18

Phil

Spring Forwards, Fall Back (How I remember it anyway)

The EU daylight saving time directive (which we in Britain follow) actually took the dates we use and applied them to the rest or europe, last sunday in March and last sunday in October.

I thought they just added the odd second here and there to account for the differences between tropical, sidreal and atomic time. To which the BBC adds an extra pip to it's time signal. The leap seconds are added at the end of the year so time goes 23:59:59, 23:59:60, 00:00:00 I think from the refernces I looked at earlier.

Anyway, is there any chance of getting a link to one of the most accurate clocks on the planet at http://tycho.usno.navy.mil/ (there is also a link to check how accurate your computer clock is smiley - smiley)


Daylight Savings

Post 19

Almighty Rob - mourning the old h2g2

Daylight savings has always been a sticking point here in Western Australia. We're out of sync with all of the other states, and yet we don't correct the time difference.

It has gone to popular referenda several times, but has always been defeated. Sadly, but humorously, the arguments against it are that the curtains will fade (due to extra sun exposure) and that the cows won't know when to be milked.

This is no joke.


Daylight Savings

Post 20

Miriam

Err.. sorry about that mistake...
I've been living in the Caribbean for the past 6 years, so I was only 11 when I last witnessed the clock being put forward/back...
Here in the Caribbean we don't do that, because there's really no point, it makes watching American tv difficult though because the schedule changes smiley - winkeye

Greetings,
Miriam

PS I bet they put the clock back when our summer starts in Australia smiley - winkeye


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