Вы хотите сказать, что ось прецессии перпендикулярна плоскости эклиптики?
Да, Вы правы.
Вот хорошее видео с рисунками. http://www.youtube.com/watch?v=CUH49R8lpYg

Ось Земли также меняет свой наклон от 22.1 до 24.5 градусов за 41000 лет

Как измеряется гравитация. Летят 2 спутника на близком расстоянии, измеряется расстояние между ними, при этом учитываются ускорения, измеряемые акселерометрами.

http://podaac.jpl.nasa.gov/gravity
[QUOTE]The Gravity Recovery And Climate Experiment (GRACE) was launched in 2002 to measure Earth's gravity field. The two identical GRACE satellites orbit one behind the other in the same orbital plane at approximate distance of 220 kilometers (137 miles). As the pair circles the Earth, areas of slightly stronger gravity (greater mass concentration) affect the lead satellite first, pulling it away from the trailing satellite. As the satellites continue along their orbital path, the trailing satellite is pulled toward the lead satellite as it passes over the gravity anomaly. The change in distance would certainly be imperceptible to our eyes, but an extremely precise microwave ranging system on GRACE detects these minuscule changes in the distance between the satellites. A highly accurate measuring device known as an accelerometer, located at each satellite's center of mass, measures the non-gravitational accelerations (such as those due to atmospheric drag) so that only accelerations cased by gravity are considered. Satellite Global Positioning System (GPS) receivers determine the exact position of the satellite over the Earth to within a centimeter or less. Members of the GRACE science team can download all this information from the satellites, and use it to construct monthly maps of the Earth's average gravity field during the planned five-year mission.[/QUOTE]

Красивые видео о Земле. http://podaac.jpl.nasa.gov/AnimationsImages/Animations
Внизу на 1-й странице: давление на океанском дне, полученное из эксперимента по измерениям гравитации и климата GRACE