Almagest study, was A fascinating book about the Sidereal zodiac...

[Guest guest]

Taking a moment to post, as I've just completed setup on an

Excel sheet to plot sidereal longitudes and latitues for all

1026 unique stars catalogued in Ptolemy's " Almagest " and

computing position errors for various epochs, enabling many

kinds of tests. I can use the date of the whole catalogue or

select stars for different criteria of precision in

positioning them.

 

Ptolemy claims July 20, 137 as the effective date of the

catalogue. If we assume that date and simply average out the

longitude errors, we find that zero Aries theoretically

matched the vernal equinox point on Julian Date 1739930 (2

Sep 51 CE). Now that's using the entire body of data, which

doubtless includes a few serious transcription errors as

well as errors consistent with the limitations of measuring

apparatus, etc.

 

As error tolerance is reduced by the trade-off of discarding

progressively more data, that reference date slides forward

within the same decade, but 52 - 54 CE looks fairly

reasonable, consistent with his placement of Aldebaran and

Antares at 12º40' of their respective signs, rather than the

15º typically cited.

 

Ernie Wright developed a nice little graphic freeware

program called " Almagest Stars " , which incorporates some of

Grasshoff's work ... I'm hoping to acquire the text you

mentioned. I'ts just a delight working with the data, even

if I don't get around to doing everything I'd like. At least

it's a handy list of so many noteworthy stars, about 400 of

which have been named by various cultures over time.

 

Well yes, the Mercury dasa does seem to be in bloom;

retirement is but two weeks away

 

Julia

 

, Therese Hamilton

<eastwest wrote:

 

> ...so happy that you're still here. You're wonderful with

sources, so you

> must have Gerd Grasshoff's THE HISTORY OF PTOLEMY'S STAR

CATALOGUE (Studies

> of the History of Mathematics and Physical Sciences 14)

which goes into the

> topic of the source of Ptolemy's star positions.

>

> I'm looking forward to hearing more about the model you're

developing.

> There's so much controversy about the precise starting

point of the

> sidereal zodiac. We have theory, and then we'll need the

practical field

> tests.

>

> I've been wondering about your Mercury dasa...

>

> Blessings,

> Therese

>