Here are some quick answers for you without looking up detailed references.
Hope that this helps.
http://www-groups.dcs.st-and.ac.uk/~history/Mathematicians/Hipparchus.html
>Perhaps the discovery for which Hipparchus is most famous is the
discovery of precession which is due to the slow change in direction of the
axis of rotation of the earth. This work came from Hipparchus's attempts to
calculate the length of the year with a high degree of accuracy. There are
two different definitions of a 'year' for one might take the time that the
sun takes to return to the same place amongst the fixed stars or one could
take the length of time before the seasons repeated which is a length of
time defined by considering the
<http://www-groups.dcs.st-and.ac.uk/~history/Mathematicians/javascript:win1('../Glossary/equinox',350,200)>equinoxes.
The first of these is called the
<http://www-groups.dcs.st-and.ac.uk/~history/Mathematicians/javascript:win1('../Glossary/sidereal_year',350,200)>sidereal
year while the second is called the
<http://www-groups.dcs.st-and.ac.uk/~history/Mathematicians/javascript:win1('../Glossary/tropical_year',350,200)>tropical
year.
Of course the data needed by Hipparchus to calculate the length of these
two different years was not something that he could find over a few years
of observations. Swerdlow [19] suggests that Hipparchus calculated the
length of the tropical year using Babylonian data to arrive at the value of
1/300 of a day less than 365 1/4 days. He then checked this against
observations of equinoxes and
<http://www-groups.dcs.st-and.ac.uk/~history/Mathematicians/javascript:win1('../Glossary/solstice',350,200)>solstices
including his own data and those of
<http://www-groups.dcs.st-and.ac.uk/~history/Mathematicians/Aristarchus.html>Aristarchus
in 280 BC and Meton in 432 BC. Hipparchus also calculated the length of the
sidereal year, again using older Babylonian data, and arrived at the highly
accurate figure of 1/144 days longer than 365 1/4 days. This gives his rate
of precession of 1 deg per century. <
* N M Swerdlow, Hipparchus's determination of the length of the
tropical year and the rate of precession, Arch. Hist. Exact Sci. 21 (4)
(1979/80), 291-309.
J Norman Lockyer evaluated Egyptian temple alignments in his book "The Dawn
of Astronomy", MIT Press, Cambridge, MA, 1894, reprinted 1964. He gives
temple orientations vs. date of construction, and he also discusses
pyramids. His magnetic azimuth measurements are accurate to at best 1/4
degree. The temple of Amon Ra (Re) at Karnak is accurately aligned to the sun.
http://www.crystalinks.com/gpstats.html
Gives dimensions, alignments and angles for the Great Pyramid, but no
scientific analysis.
Naked eye astronomical measurements (with graduated instruments) reached
their greatest accuracy with the plain sights of Tycho Brahe and Johannus
Hevelius: accuracy on the order of 30" for stars or the sun. Ptolemy and
earlier astronomers used peephole sights, which were less precise.
Plain sights are an interest of mine and I would be happy to discuss them
with anyone interested.
Gordon Uber
San Diego
At 02:06 2/18/05, anselmo wrote:
Dear dialists,
Yes, I know this is old hat, but
does anybody know how could Hipparcus
know the longitude of a tropical year
with a 4-digit precission? More
generally, which is the highest
accuracy one can expect from naked-eye
observations to equinoxes, solstices,
NSEW points, and so on... Is it true
that some egyptian temples are aligned
up to the arc-minute or is it just
science-lore?
Regards,
Anselmo
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