Re: Happy Solstice, y'all


"Julia Altshuler" <jaltshuler@xxxxxxxxxxx> wrote in message
I don't know if any allowance was made. To me, the more interesting
question is how much was known about precession 2000 years ago. I'd guess
that the fact that the night sky changed in slight but noticeable ways was
apparent. But understanding that the earth's axis was changing in its
relationship to the sun? I'm not so sure. That would require
understanding that the earth rotating on an axis, was revolving around the
sun, and that the axis was changing in its relationship to the sun. I'm
not sure that the ancients grasped all that, although they might have.


I've got a copy of _Hamlet's Mill_ somewhere in my basement. I might have
to dig it up and take a look. Or perhaps you can recommend a more
up-to-date source on archaeoastronomy?

I sometimes wonder just how little we know in comparison to the ancients.
Sure, we have rocket ships and computers, but given the tools of the day and
the lifespan of humans back then, the powers of observations were
incredible. Watching the sky every night how long does it take to know the
pattern of the seasons and repeatability?

I did just find this though, putting that knowledge at 2300 years ago.
http://en.wikipedia.org/wiki/Precession
Discovery of the precession of the equinoxes is generally attributed to the
ancient Greek astronomer Hipparchus (ca. 150 B.C.), though the difference
between the sidereal and tropical years was known to Aristarchus of Samos
much earlier (ca. 280 B.C.). It was later explained by Newtonian physics.
The Earth has a nonspherical shape, being oblate spheroid, bulging outward
at the equator. The gravitational tidal forces of the Moon and Sun apply
torque as they attempt to pull the equatorial bulge into the plane of the
ecliptic. The portion of the precession due to the combined action of the
Sun and the Moon is called lunisolar precession.


Since we don't have written records before that time, could they have known?


.

Relevant Pages

  • Re: Reason for Procession of the Equinox?
    ... > precession itself. ... That is a slight clockwise motion of the top's axis. ... that spin interacts with the direction of gravity's pull. ... over to the Earth and the Moon. ...
    (sci.astro.amateur)
  • Re: Reason for Procession of the Equinox?
    ... it's the fact that the Moon doesn't quite ... Sun and Moon, as in lunisolar precession. ... gravitational force on the Earth. ...
    (sci.astro.amateur)
  • Re: Reason for Procession of the Equinox?
    ... > contribution to Earth's wobble is called nutation. ... The reading I've had suggests that both the Moon and the Sun are ... responsible for precession; it's the fact that the Moon doesn't quite ...
    (sci.astro.amateur)
  • Re: Geosynchronous orbits
    ... If the orbit were directly over the poles, ... If the Sun were over the equator, there's no net external toque on the ... In a model where the spin axis lies in the orbital plane, precession ...
    (sci.astro.amateur)
  • Re: Orbital precession w/o GR
    ... nearest approach to the sun along the orbital plane," whatever the ... there was still some 'precession' left over. ... The model is a rotating rigid body. ...
    (sci.physics.relativity)
Loading