Anathem (Page 1)
Jan. 16th, 2009 11:46 amMy God! Neal Stephenson was bitten by a radioactive library, and turned into an unholy cross between Umberto Eco and <Reverb>Tolkien</Reverb>.
Jan. 16th, 2009
For the purposes of this story, I'm going to assume that days, lunar months, and solar (vernal) years have a fixed duration of 24h, 29.53xx days and 364.2429 days respectively. (If you want the details, someone will explain in the comment section below.)
In the old days (TM) [1] people tended to have days and nights, and lunar festivals (eg. at full moon), and annual festivals (eg. at spring), but not to have complicated accounting practices. Thus it was easy to say "A year begins at solstice (or equinox, or etc etc), a month begins with a new moon (etc etc), and a day begins at sunset (or midnight, or dawn, etc)" and not worry whether you knew exactly what day the year started on, or if there were always the same numbers of months. And many, many ancient people had calendars based on many variations on this theme.
( Read more... )
In the old days (TM) [1] people tended to have days and nights, and lunar festivals (eg. at full moon), and annual festivals (eg. at spring), but not to have complicated accounting practices. Thus it was easy to say "A year begins at solstice (or equinox, or etc etc), a month begins with a new moon (etc etc), and a day begins at sunset (or midnight, or dawn, etc)" and not worry whether you knew exactly what day the year started on, or if there were always the same numbers of months. And many, many ancient people had calendars based on many variations on this theme.
( Read more... )
Hebrew calender (continued)
Jan. 16th, 2009 03:55 pmLeap things
OK, so that's the history. Let's see if I actually understand the Hewbrew calendar.
As I understand it, the Gregorian calendar is defined to use an average year length of 365.2425, or 365*400+97 days in every 400 years. That is, even if you're not quite certain of the distribution of leap years, if the Gregorian calendar were to be used forever, if you knew a date was 1000000000000 days in the future, you could predict the year simply with that value, and always be right. (Maybe a day off if you didn't know which year the leap years came in).
The actual distribution of those days is semi-arbitrarily chosen. There's two major approaches to that. You normally want the changes to be roughly equally spaced so the intermediate years don't drift too far, and you don't get a sudden 97 days you're not sure what to do with at the end of the 400 year cycle.
( Read more... )
Is that about right?
[1] Why those? Because Yom Kippur happens shortly afterwards, and (supposedly[2]) shouldn't be ADJACENT to a Saturday (because Saturday is shabbat and you don't want the prohibitions of shabbat directly abbutting those of yom kippur). And the festival of knocking things over occurs shortly after that, and shouldn't be ON a shabbat (because you can't knock things over on a shabbat). Fortunately, these dates are a fixed number of days away from each other, and away from 1st Tishrei, so both of these commitments can be honoured at once.
[2] Apparently people aren't completely sure why this fiddle exists.
OK, so that's the history. Let's see if I actually understand the Hewbrew calendar.
As I understand it, the Gregorian calendar is defined to use an average year length of 365.2425, or 365*400+97 days in every 400 years. That is, even if you're not quite certain of the distribution of leap years, if the Gregorian calendar were to be used forever, if you knew a date was 1000000000000 days in the future, you could predict the year simply with that value, and always be right. (Maybe a day off if you didn't know which year the leap years came in).
The actual distribution of those days is semi-arbitrarily chosen. There's two major approaches to that. You normally want the changes to be roughly equally spaced so the intermediate years don't drift too far, and you don't get a sudden 97 days you're not sure what to do with at the end of the 400 year cycle.
( Read more... )
Is that about right?
[1] Why those? Because Yom Kippur happens shortly afterwards, and (supposedly[2]) shouldn't be ADJACENT to a Saturday (because Saturday is shabbat and you don't want the prohibitions of shabbat directly abbutting those of yom kippur). And the festival of knocking things over occurs shortly after that, and shouldn't be ON a shabbat (because you can't knock things over on a shabbat). Fortunately, these dates are a fixed number of days away from each other, and away from 1st Tishrei, so both of these commitments can be honoured at once.
[2] Apparently people aren't completely sure why this fiddle exists.