which day of the week

[SpriggsySpriggs]

From Julian to Gregorian, yes.

[SierraKen]

Chat GPT says it was a Saturday on Jan. 1, 1 A.D., but only if you go by the Julian Calendar and count back. If you go back in time in a time machine, they didn't have our weekdays until 321 A.D. Before that there were other weekdays, like the 8 day Roman one, or 7 day ones by other groups (Christians, Jewish, Babylonians). But it wasn't universally made until 321 A.D. by Constantine.

[Pete]

Hope to clear things up a bit with this Columbus Day demo, but short answer... When was Columbus Day in 1492? No day... It hadn't been invented until 1971.

Anyway, the demo shows all leap years in yellow, non in white. It shows the difference in calendar days for each year, 365 or 366 (except the first year, 1492). What you will notice that unless it is a leap year the progression is the next day each year. On a leap year it skips to the day after next. The pattern proves if the algorithm used is correct.

Code: (Select All)

' Columbus Day "Day of the Week" from 1492 on...

' Using Gregorian calendar algorithm, which was not available (invented) until 1582.

Width 80, 43

_ScreenMove 0, 0

map$ = "Sunday    Monday    Tuesday  Wednesday Thursday  Friday    Saturday"

year = 1492

month = 10

Rem January = 0, February = 31,March = 59, April = 90, May = 120, June = 151, July = 181, August = 212,,September = 243, October = 273, November = 304 and December = 334

oct = 273

day = 12

Do

    leapyear = 0

    ans = (365 * year) + year \ 4 - year \ 100 + year \ 400 - 365

    If year Mod 4 = 0 And year Mod 100 Or year Mod 4 = 0 And year Mod 100 = 0 And year Mod 400 = 0 Then leapyear = 1

    If leapyear And month < 3 Then ans = ans - 1

    ans = ans + oct + day

    dow = ans Mod 7

    If leapyear Then Color 14 Else Color 7

    Print year, ans, ans - oldans, "Oct 12,"; year; "falls on a " + Mid$(map$, 10 * dow + 1, 10)

    year = year + 1

    oldans = ans

    Sleep

Loop

Pete

[bplus]

Chat GPT says it was a Saturday on Jan. 1, 1 A.D., but only if you go by the Julian Calendar and count back. If you go back in time in a time machine, they didn't have our weekdays until 321 A.D. Before that there were other weekdays, like the 8 day Roman one, or 7 day ones by other groups (Christians, Jewish, Babylonians). But it wasn't universally made until 321 A.D. by Constantine.

Actually I was going for the very first day of AD in the year 0.

Remember you need to go a whole year, 365+ days before year 1 starts.

But sure, at that time nobody knew it was AD yet

[macalwen]

October 4, 1582 week 4, before this date the Julian calendar was used, with a leap year every 4 years, and working backwards from this, then January 1, 1 AD was week 6, October 5 to 14, 1582 was canceled, so October 15, 1582 was week 5, and from this date onwards the Gregorian calendar was used, with a slightly different calculation of leap years. To take all of this into account, it can only be calculated separately.

[Pete]

October 4, 1582 week 4, before this date the Julian calendar was used, with a leap year every 4 years, and working backwards from this, then January 1, 1 AD was week 6, October 5 to 14, 1582 was canceled, so October 15, 1582 was week 5, and from this date onwards the Gregorian calendar was used, with a slightly different calculation of leap years. To take all of this into account, it can only be calculated separately.

I put a +2 on your initial post for addressing the calendar change up. It made me decide to stop my routine from going back prior to 1583. I use it for appointments, so unless I make a time machine... Which if I ever do you'd think I know about it by now, going back in times past the first day of use was not something I was concerned about. At least now it can't be misused in that regard,

Pete