when was it first discovered that Earth's obliquity oscillates?

In article ,
Denis Roegel wrote:
I am trying to understand what was the knowledge of the precession
of the equinoxes in 1840, and this leads me to search the theory
of Earth's obliquity. I need to find out when it was discovered that
the obliquity oscillates, and not merely decreases (as it currently
does). For instance, the Connaissance des temps around 1840 only tells
about a decrease of 48" by century. No oscillation is mentioned.
Was it because the oscillation theory was not known? And if it was
known, who was the first to publish it and where?

The ecliptic that is used in dynamical theories is a secularly changing
plane which by definition does not have periodic components. The Earth-
Moon Barycentre does meander north and south of this slowly tilting plane
of course, by a few arcseconds, and this is presumably what you are
referring to. In other words the ecliptic is a sort of moving average.


Patrick Wallace
__________________________________________________ __________________________
Starlink/HMNAO Internet:
Rutherford Appleton Laboratory Tel: +44-1235-445372
Chilton, Didcot, Fax: +44-1235-446362
Oxon OX11 0QX, UK
__________________________________________________ __________________________

In article ,
Denis Roegel wrote:
I am trying to understand what was the knowledge of the precession
of the equinoxes in 1840, and this leads me to search the theory
of Earth's obliquity. I need to find out when it was discovered that
the obliquity oscillates, and not merely decreases (as it currently
does). For instance, the Connaissance des temps around 1840 only tells
about a decrease of 48" by century. No oscillation is mentioned.
Was it because the oscillation theory was not known? And if it was
known, who was the first to publish it and where?

The ecliptic that is used in dynamical theories is a secularly changing
plane which by definition does not have periodic components. The Earth-
Moon Barycentre does meander north and south of this slowly tilting plane
of course, by a few arcseconds, and this is presumably what you are
referring to. In other words the ecliptic is a sort of moving average.


Patrick Wallace
__________________________________________________ __________________________
Starlink/HMNAO Internet:
Rutherford Appleton Laboratory Tel: +44-1235-445372
Chilton, Didcot, Fax: +44-1235-446362
Oxon OX11 0QX, UK
__________________________________________________ __________________________

In article ,
Bill Owen wrote:
:
That's not quite what the original poster had in mind.
:
If you expand the perturbation equations, you'll find terms containing
the sine or cosine of the longitude of the ascending node and of the
longitude (or argument) of perihelion. These produce long-period
perturbations -- the periods are typically 10^4 to 10^5 years -- and
the discovery of these terms is the subject of the original poster's
question. The cubic polynomials in T are merely the leading terms of
a Taylor expansion.

Yes you're right- I was thinking of the short term, over which the
operational models of planetary precession are accurate, rather than
tens of thousands of years. The best references I've found on the web
are these:

http://www.geo.arizona.edu/palynolog...climastro.html

http://aa.usno.navy.mil/faq/docs/seasons_orbit.html

It seems that some of this dates back to Joseph Adhemar and James Croll
in the 19th century, long before Milankovitch. But as Newcomb and
LeVerrier were both working from perturbation theory, presumably they
knew about the long-period oscillations, and I guess Adhemar and Croll
were coming at it more from a climatological standpoint.

Patrick Wallace
-----------------------------------------------------------------------

In article ,
Bill Owen wrote:
:
That's not quite what the original poster had in mind.
:
If you expand the perturbation equations, you'll find terms containing
the sine or cosine of the longitude of the ascending node and of the
longitude (or argument) of perihelion. These produce long-period
perturbations -- the periods are typically 10^4 to 10^5 years -- and
the discovery of these terms is the subject of the original poster's
question. The cubic polynomials in T are merely the leading terms of
a Taylor expansion.

Yes you're right- I was thinking of the short term, over which the
operational models of planetary precession are accurate, rather than
tens of thousands of years. The best references I've found on the web
are these:

http://www.geo.arizona.edu/palynolog...climastro.html

http://aa.usno.navy.mil/faq/docs/seasons_orbit.html

It seems that some of this dates back to Joseph Adhemar and James Croll
in the 19th century, long before Milankovitch. But as Newcomb and
LeVerrier were both working from perturbation theory, presumably they
knew about the long-period oscillations, and I guess Adhemar and Croll
were coming at it more from a climatological standpoint.

Patrick Wallace
-----------------------------------------------------------------------

In article ,
(Denis Roegel) writes:

I am trying to understand what was the knowledge of the precession
of the equinoxes in 1840, and this leads me to search the theory
of Earth's obliquity.

No, I am looking for the discovery of the 41000 years oscillation period,
known as the Milankovitch cycle. Who first discovered it? Was it Milankovitch?

It's been 25 years or so since I read it, but I recall an essay called
"Oblique the centric globe" in one of Isaac Asimov's F&SF essay
collections, which dealt with this topic.

See http://homepage.mac.com/jhjenkins/Asimov/Asimov.html for an
interesting resource concerning the writings of Asimov.

Unfortunately, I don't recall which of the many collections it was in!

In article ,
(Denis Roegel) writes:

I am trying to understand what was the knowledge of the precession
of the equinoxes in 1840, and this leads me to search the theory
of Earth's obliquity.

No, I am looking for the discovery of the 41000 years oscillation period,
known as the Milankovitch cycle. Who first discovered it? Was it Milankovitch?

It's been 25 years or so since I read it, but I recall an essay called
"Oblique the centric globe" in one of Isaac Asimov's F&SF essay
collections, which dealt with this topic.

See http://homepage.mac.com/jhjenkins/Asimov/Asimov.html for an
interesting resource concerning the writings of Asimov.

Unfortunately, I don't recall which of the many collections it was in!