Re: ASTROGRAPH OF VAT4956 LINE 8

"Moshiachyozif" <siaxares@xxxxxxxxxxxxxx> wrote:

This imaginary axis... this is something akin to the right ascension
of the star in question? Is it always a North-South line?

Or is it something else entirely?

I am not certain, but reading observations it appears there was some
standard instrument they used to calculate their observations. There are
some lists that give the adjusted or rounded distances between stars that
was standardized. The visual distance of course changes as the night
progresses.

Wait... um, what? Since when? The effect due to refraction is very
small - about half a degree when you're looking at a star right on the
horizon, rapidly decreasing as the star's altitude increses. Above
perhaps 20° altitude, relative stellar positions are rock solid for
naked eye measurements. The relative positions of the stars in the
bulk of the visible star field would not have changed throughout the
night for ancient astronomers.

So in practical application if you imagine an instrument like
a cross that has hatch marks made on both axis to measure distances, it
could be adjusted closer or father from the eye until the predetermined
present distance was determined and then a specific calculation made based
on that.

Yep, there's a name for that device, which I've been trying to
remember for two days.

So, each observer had one of these instruments--but were all observers
using instruments having cross-pieces of equal lengths? The length of
the cross-piece being used would change the number of cubits between
stars.

The length of the staff would also matter, since some particular
length had to be chosen for 1 cubit, since they couldn't make an
arbitrarily long staff to measure arbitrarily small separations.

That also means that thier cubit scale for angular separation isn't
linear, but more like the arctangent function.

And, depending on the direction the staff was numbered, 2 cubits could
be a smaller angular separation than 1 cubit.

--
Dave

.

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