Compass directions

[tijlan]

FAhA1 (ex. "ne'u") and FAhA2 (ex. "ni'a")... are they fundamentally
different sets of concepts, not sharing any semantic prime? Or is it a
matter of reference frame (ma'i, VIhA)?

Can "snanu" be defined in terms of other than "berti"?

mu'o

[tijlan]

si

On 14 December 2011 10:35, tijlan <jbot...@gmail.com> wrote:
> FAhA1 (ex. "ne'u") and FAhA2 (ex. "ni'a")... are they fundamentally
> different sets of concepts, not sharing any semantic prime?

Well, they must both mean farna. Apart from that.

mu'o

[Jorge Llambías]

On Wed, Dec 14, 2011 at 7:35 AM, tijlan <jbot...@gmail.com> wrote:
>
> Can "snanu" be defined in terms of other than "berti"?

How about "the direction to your right when facing in the direction in
which the sun rises (in case you don't want to use "stuna" either).

mu'o mi'e xorxes

[tijlan]

2011/12/14 Jorge Llambías <jjlla...@gmail.com>:

There are two kinds of south: geological south and magnetic south. The
geological one represents the point where the planet's axis of
rotation meets its surface, also called the south pole. The magnetic
one represents the force field that extends from the planet's inner
core. Magnetic south & north can wander off from geological ones. The
difference creates an angle called magnetic declination, which has
been increasing recently as the Earth's magnetic field is shifting,
causing troubles for airports. Today's magnetic south was north
10,000+ years ago. During a geomagnetic reversal, there can be
multiple souths, looking something like this:

http://upload.wikimedia.org/wikipedia/commons/e/e5/NASA_54559main_comparison1_strip.gif

Sunrise has to do with the axis of rotation, so your suggestion would
work for the geological one, but the other kind of south is
independent of that axis.

Every planet in our solar system has a south pole, but at a different
angle. While the Earth is tilted by about 23.5 degree, Uranus is by
nearly 98 degree -- one pole facing the sun throughout a day --,
resulting in very different conditions for sunrise/sunset (and
seasons).

mu'o

[guskant]

coi

2011/12/15 tijlan <jbot...@gmail.com>:

> There are two kinds of south: geological south and magnetic south. The

> geological one represents the point where the planet's axis of

> rotation meets its surface, also called the south pole. 

The axis of rotation also shifts depending on kinetic conditions.

The terrestrial (map) poles are almost fixed to the Earth, but they may shift with regard to horizontal tectonic motions:

http://www.iers.org/nn_10968/IERS/EN/DataProducts/ITRS/itrs.html?__nnn=true

There are also celestial poles.

There are therefore at least four kinds of south: celestial south, south of a map, "south" (or rather a negative pole) of rotation, south of magnetic field.

1. Celestial south

According to the International Astronomical Union, 

http://www.iau.org/static/resolutions/IAU2000_French.pdf

the celestial poles are defined depending on the Earth's revolution around the sun (Nos. B1.7 + B1.3 for the Celestial Intermediate Pole). 

2. South of a map

The terrestrial poles are defined depending on the Celestial Intermediate Pole (No. B1.8 for the International Terrestrial Reference System).

3. Pole of rotation 

A positive pole ("north") of rotation is defined with so-called right-hand grip rule. 

http://en.wikipedia.org/wiki/File:Manoderecha.svg

"South", or rather a negative pole of rotation is the opposite side.

This definition is applied to asteroids and comets:

http://www2.keck.hawaii.edu/inst/people/conrad/research/pub/WGCCRE2009-preprint.pdf

4. South of magnetic field

South of magnetic field is rather complicated. 

A magnetic field is a vector field. 

The south pole of a magnet is the point to which line integrals of magnetic field point toward; the north pole of a magnet is the point from which line integrals of magnetic field point away.

The South Pole of the Earth is the north pole of a magnet that attracts the south pole of another magnet. 

A magnet may have more than two poles.

Some celestial bodies form very complicated magnetic fields. For example, the Sun forms a rotating magnetic field: http://en.wikipedia.org/wiki/File:Heliospheric-current-sheet.gif

The poles of 1, 2, 3 are defined as two ends of an axis, but the poles of 4 are not necessarily on an axis. In other words, north and south of 1, 2, 3 can be defined dependent on each other, or dependent on the definition of the axis; on the other hand, north(s) and south(s) of 4 should be defined independently.

mi'e guskant mu'o