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« Return to Thread: Why was Pope Gregory's adjustment 10 days not 8 days?
Re: Why was Pope Gregory's adjustment 10 days not 8 days?
by Brillig
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Dear Calendar People,
Just out of curiosity, using the information at
http://en.wikipedia.org/wiki/Hipparchus I decided to calculate the
mean year length between Hipparchus' observation in 146 BC at dawn and
this year's equinox as tabulated in wikipedia. I get a mean year
length of 365.242415 days (assuming dawn at Rhodes is 7.86 UT,
calculated from 28 degrees east). If I use instead the one hour before
noon time also mentioned in the article, I get instead 365.242318
days.
Victor
On Fri, May 1, 2009 at 11:26 AM, Irv Bromberg <irv.bromberg@...> wrote:
> On 2009 May 1, at 11:41 , Palmen, KEV (Karl) wrote:
>
> Irv wrote: On the contrary, I have shown that March 21st was the correct
> date, assuming it was reckoned at Alexandria with the calendar day starting
> at sunset, as was the practice at the time, see
> <http://www.sym454.org/mar21/>. Also, the ecclesiastical equinox refers to
> the first day that is in the spring season, which was without doubt March
> 21st in 325 AD in Alexandria.
>
> If this were so for the Julian Calendar, it would have been March 22 for the
> Proleptic Gregorian calendar. Four 400-year cycles later in 1925 the equinox
> was March 21st 03:12 according to http://stellafane.org/misc/equinox.html .
> ,so giving a date of March 21st (12th hour) in Alexandria. So a drift of
> over half a day would be necessary to make it 22nd March in the proleptic
> Gregorian 1600 years earlier (I’ve chosen a multiple of 400 years to
> eliminate calendar jitter). This is sufficient argument to show that the
> date was wrong. Also I recall another E-mail that said that the date was got
> from Ptolemy who reckoned that the tropical year was 1/300 day short of 365
> ¼ days.
>
> Irv replies: I've never heard of there ever having been any intention of
> making the equinox land on March 21st in 325 AD on the proleptic Gregorian
> calendar. This seems implausible to me.
> Notwithstanding Karl's argument, the actual northward equinox reckoned for
> the meridian of Alexandria was just before noon on March 21st on the
> proleptic Gregorian calendar, so no problem there.
> Julian March 21st would have started at the sunset about 6+1/4 hours later,
> making Julian March 21st the ecclesiastical first day of spring.
>
> -- Irv Bromberg, Toronto, Canada
> <http://www.sym454.org/mar21/>
> <http://www.sym454.org/seasons/>
> <http://www.sym454.org/leap/>
Just out of curiosity, using the information at
http://en.wikipedia.org/wiki/Hipparchus I decided to calculate the
mean year length between Hipparchus' observation in 146 BC at dawn and
this year's equinox as tabulated in wikipedia. I get a mean year
length of 365.242415 days (assuming dawn at Rhodes is 7.86 UT,
calculated from 28 degrees east). If I use instead the one hour before
noon time also mentioned in the article, I get instead 365.242318
days.
Victor
On Fri, May 1, 2009 at 11:26 AM, Irv Bromberg <irv.bromberg@...> wrote:
> On 2009 May 1, at 11:41 , Palmen, KEV (Karl) wrote:
>
> Irv wrote: On the contrary, I have shown that March 21st was the correct
> date, assuming it was reckoned at Alexandria with the calendar day starting
> at sunset, as was the practice at the time, see
> <http://www.sym454.org/mar21/>. Also, the ecclesiastical equinox refers to
> the first day that is in the spring season, which was without doubt March
> 21st in 325 AD in Alexandria.
>
> If this were so for the Julian Calendar, it would have been March 22 for the
> Proleptic Gregorian calendar. Four 400-year cycles later in 1925 the equinox
> was March 21st 03:12 according to http://stellafane.org/misc/equinox.html .
> ,so giving a date of March 21st (12th hour) in Alexandria. So a drift of
> over half a day would be necessary to make it 22nd March in the proleptic
> Gregorian 1600 years earlier (I’ve chosen a multiple of 400 years to
> eliminate calendar jitter). This is sufficient argument to show that the
> date was wrong. Also I recall another E-mail that said that the date was got
> from Ptolemy who reckoned that the tropical year was 1/300 day short of 365
> ¼ days.
>
> Irv replies: I've never heard of there ever having been any intention of
> making the equinox land on March 21st in 325 AD on the proleptic Gregorian
> calendar. This seems implausible to me.
> Notwithstanding Karl's argument, the actual northward equinox reckoned for
> the meridian of Alexandria was just before noon on March 21st on the
> proleptic Gregorian calendar, so no problem there.
> Julian March 21st would have started at the sunset about 6+1/4 hours later,
> making Julian March 21st the ecclesiastical first day of spring.
>
> -- Irv Bromberg, Toronto, Canada
> <http://www.sym454.org/mar21/>
> <http://www.sym454.org/seasons/>
> <http://www.sym454.org/leap/>
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