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Dates That Don't Exist (2015)

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Re: Dates That Don't Exist (2015)

#81

Post by pasc1878 »

Cthulhu_ wrote: post #6
laveur wrote: post #2

I tried to create a date object in Swift from the date October 5, 1582. The resultant date object was October 15th 1582.

This is (weirdly) in line with behaviour I've observed in iOS's date picker; if you set a block of dates as not available, and the selected date inside of that unavailable block, it will automatically select the first available date on open.

Why is that weird. They are both using Apple code - Swift probably has to meet Objective C dates or even uses the Objective C date functions.

Re: Dates That Don't Exist (2015)

#82

Post by pasc1878 »

autarch wrote: post #41
dinkelberg wrote: post #38

Earlier quoted context omitted.

Who else uses the proleptic Gregorian calendar other than programmers of datetime libraries?

Who writes computer programs that deal with pre-1582 _dates_ at all? In science-related code, I can image a case for calculating things like seconds elapsed across a very long time period. But in that case you're not really dealing with dates. Instead, you want something like the Unix epoch, but probably with an earlier epoch start. There may be some very niche cases for pre-1582 dates in code that I'm not thinking o…

For astronomical code (and any sane date code) you use Julian Day Number which is the number of days since a defined day 0.

The one most seen would be Microsoft DateTime first in Excel where day 1 is 31st Dec 1899 in USA/Georgian Calendar - but only useful from March 1st 1900

Wikipedia gives the Astronomical Day number as

The Julian day number (JDN) has the same epoch as the Julian period, but counts the number of days since the epoch rather than the number of years since then. Specifically, Julian day number 0 is assigned to the day starting at noon Universal Time on Monday, January 1, 4713 BC, proleptic Julian calendar (November 24, 4714 BC, in the proleptic Gregorian calendar).[4][5][6][a] For example, the Julian day number for the day starting at 12:00 UT (noon) on January 1, 2000, was 2451545.[7]

There is the Modified Julian Dates several of which including the Microsoft one are listed in Variants here https://en.wikipedia.org/wiki/Julian_day

Re: Dates That Don't Exist (2015)

#83

Post by Telaneo »

tomjakubowski wrote: post #74
autarch wrote: post #41

Earlier quoted context omitted.

Who writes computer programs that deal with pre-1582 _dates_ at all? In science-related code, I can image a case for calculating things like seconds elapsed across a very long time period. But in that case you're not really dealing with dates. Instead, you want something like the Unix epoch, but probably with an earlier epoch start. There may be some very niche cases for pre-1582 dates in code that I'm not thinking o…

Genealogical software, historical video games (CK2 has at least one mod which adds alternative calendars), I can imagine there are some needs for this in contract management software for countries with very old businesses and properties like England and Japan.

> (CK2 has at least one mod which adds alternative calendars)

I imagine that must have been absolutely riveting to mod in.

Re: Dates That Don't Exist (2015)

#84

Post by wduquette »

cjm42 wrote: post #79
wduquette wrote: post #42

Using the proleptic Gregorian calendar for historical dates is only a problem if you want to compute the day of the week (which those missing days will throw off prior to the adoption of the Gregorian calendar in the relevant country) or the number of days between two historical dates (if the two dates span the date when the Gregorian calendar was adopted). And, frankly, there are other problems to deal with beyond c…

As da_chicken pointed out, it's also a problem if you want to record a date like February 29, 1700, which is a perfectly valid date in the Julian calendar but simply doesn't exist in the proleptic Gregorian calendar. Dates are messy.

Fair point.

Re: Dates That Don't Exist (2015)

#85

Post by orhmeh09 »

autarch wrote: post #41
dinkelberg wrote: post #38

Earlier quoted context omitted.

Who else uses the proleptic Gregorian calendar other than programmers of datetime libraries?

Who writes computer programs that deal with pre-1582 _dates_ at all? In science-related code, I can image a case for calculating things like seconds elapsed across a very long time period. But in that case you're not really dealing with dates. Instead, you want something like the Unix epoch, but probably with an earlier epoch start. There may be some very niche cases for pre-1582 dates in code that I'm not thinking o…

People working with buildings, infrastructure, and artifacts that predate 1582. Many such things in Europe

Re: Dates That Don't Exist (2015)

#86

Post by NetMageSCW »

bloppe wrote: post #54
deathanatos wrote: post #47

> In essence, then, those ten days in 1582 never happened and simply do not exist within the Gregorian calendar system used almost universally in the West today. I find these things so much easier to think about if you consider the change as a change from one calendar system to another calendar system. Those 10 days certainly exist, in both calendar systems, they just represent different points in time. I.e., I think…

> Those 10 days certainly exist, in both calendar systems. Not in the standard Gregorian calendar. Those dates only exist in the proleptic Gregorian calendar. The standard Gregorian calendar explicitly skips them. That's because you can't feasibly go back and change all the Julian dates that had been physically written down for centuries. That's why it's called the Gregorian "shift".

The standard Gregorian calendar in which country?

Re: Dates That Don't Exist (2015)

#87

Post by NetMageSCW »

da_chicken wrote: post #67
Asraelite wrote: post #51

Earlier quoted context omitted.

I would say it's almost never appropriate unless you're directly quoting source texts. If you are talking about a historical event from Egypt in 500 BCE, you would say "this happened in 500 BCE", not "this happened in year 26 of the 27th dynasty". The distinction is important in the context of doing historical research, but it is no more appropriate to write dates in secondary sources using the Julian calendar than i…

Yeah, but how often are we talking about exactly specific dates without referring to specific historical texts? The Magna Carta was sealed on June 15, 1215 for the Julian calendar. But if you want the actual anniversary, it was sealed on June 22, 1215 using the proleptic Gregorian calendar. Do you want to know the date people remember, ir the date of the true anniversary? The coronation of Henry VIII is listed almost…

What happens when you try to talk about the age of George Washington?

Re: Dates That Don't Exist (2015)

#88

Post by bloppe »

NetMageSCW wrote: post #86
bloppe wrote: post #54

Earlier quoted context omitted.

> Those 10 days certainly exist, in both calendar systems. Not in the standard Gregorian calendar. Those dates only exist in the proleptic Gregorian calendar. The standard Gregorian calendar explicitly skips them. That's because you can't feasibly go back and change all the Julian dates that had been physically written down for centuries. That's why it's called the Gregorian "shift".

The standard Gregorian calendar in which country?

The one introduced by Gregory. I'm not sure if countries that reformed later cared enough to use a different name, but the Gregorian calendar is pretty well defined.

Re: Dates That Don't Exist (2015)

#89

Post by da_chicken »

NetMageSCW wrote: post #87
da_chicken wrote: post #67

Earlier quoted context omitted.

Yeah, but how often are we talking about exactly specific dates without referring to specific historical texts? The Magna Carta was sealed on June 15, 1215 for the Julian calendar. But if you want the actual anniversary, it was sealed on June 22, 1215 using the proleptic Gregorian calendar. Do you want to know the date people remember, ir the date of the true anniversary? The coronation of Henry VIII is listed almost…

What happens when you try to talk about the age of George Washington?

That one is actually kind of interesting.

So he was born on Feb 11 the year before the British empire adopted the Gregorian calendar. After the change, his birthday was Feb 22. Feb 22 is the date that we generally remember. That makes sense because George himself wouldn't have any personal memory of the Julian (often called "old style" at the time) date.

However, as you'd expect of such a situation, a lot of people at the time knew the old style Feb 11 date, so he was known to acknowledge both dates to people that came up to him. Somewhat famously, the last year of his life he publicly celebrated his birthday on Feb 11 while away from home, and then upon returning to Mount Vernon he celebrated it again on Feb 22.

Re: Dates That Don't Exist (2015)

#90

Post by ewgoforth »

Every year there is an hour that doesn't exist, when the clocks spring forward from standard time to daylight savings time.

We also go through the same hour twice when the clocks go back going back to standard time.

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