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WCDT: 2455-2459 (27-31 May, 2013) Weekly Comic Discussion Thread

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PintsizeForPresident:
About the date thingy: During an astronomy course we had to convert ordinary dates into julian dates. The julian date is simply a day count, with day 0 somewhere in prehistory; this dating system makes it easy to date astronomical phenomena in a consistent fashion.

To do this conversion we had a table which showed the julian date of the start of each month. But to simplify calculations the table showed the julian date of the 0th day of each month, defined as the day before the 1st day of the month (i.e., the last day of the previous month). For instance, the table would show that 0 january 2000 is JD 2451544, which means that 13 january is JD 2451544 + 13.

pwhodges:
The pattern of the Gregorian calendar repeats every four thousand years.  I once gave as a programming exercise (to people I was teaching BCPL) to work out the differences in frequencies that each date in the month falls on each day of the week within a full cycle.  It turns out that (click to show/hide)the 13th day of the month falls more often on a Friday than any other day, and that this is the most marked deviation from the average of any date/day pairing.

Skewbrow:

--- Quote from: pwhodges on 26 May 2013, 06:05 ---The pattern of the Gregorian calendar repeats every four thousand years. 

--- End quote ---
I think four hundred years is enough, if you only worry about which day of the week falls on which date. This is because in every span of 400 years there are exactly 97 leap years. On a regular year the calendar moves up one week day (because 365 is congruent to 1 modulo 7), and on a leap year the calendar moves up 2 week days (well, there will be one extra day). Therefore in a span of 400 years the calendar will have moved up 400+97=497 days, which is a multiple of seven, so the calendar repeats.

This, of course, ignores things like the location of the Easter which depends on the cycle of full moons. Because the length of the Moons period is (most likely) not a rational multiple of days (and it actually varies, as tidal forces and such affect the Moon's motion), that is unlikely to repeat exactly. At least not from here to eternity. Well, the Gregorian calendar itself will deviate from the "true" Solar calendar eventually, so this last point is kinda moot.

Method of Madness:

--- Quote from: Sidhekin on 26 May 2013, 01:35 --- The Sabbath is the seventh day (day 6 to old-style low-level programmers), and it's (usually?) recognized as Saturday.

Sunday is the Holy Day, though
--- End quote ---
I thought Sunday was the Sabbath (and therefore the holy day) in at least most branches of Christianity.

Zebediah:
"Sabbath" refers specifically to the Jewish observance, which is from Friday at sundown to Saturday at sundown. In most branches of Christianity Sunday is the "Lord's Day", which has taken on some of the functions and symbolism of the Jewish sabbath and which is therefore sometimes called the "Christian sabbath".

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