Newton had suggested that, on the basis of his gravitational theory, the Earth ought to be an oblate spheroid and have an equatorial bulge
, because it was rotating (see 1687, Universal Gravitation).
In the case of Earth, the attractions of the Sun and Moon on our planet's equatorial bulge
try to tilt up the axis to make it perpendicular to the plane of the ecliptic.
The tip of the highest, the gargantuan 6,310-metre Chimborazo, is the farthest point from the Earth's centre (owing to the equatorial bulge
Its perigee (the point of its closest approach to the Earth) moved somewhat with each revolution, in part because of the gravitational pull of the Earth's equatorial bulge
16 SCIENCE, Coffey and his colleagues applied their visualization technique to a simplified set of equations that included deviations caused only by the Earth's equatorial bulge
. Now they can add in much smaller perturbations to get results useful to engineers planning satellite orbits that lie between 300 and 2,000 miles above the Earth's surface, says Andre Deprit of the National Institute of Standards and Technology in Gaithersburg, Md., who developed the technique with Coffey and NRL colleagues Etienne Deprit and Liam Healy.
The Sun and Moon tug on the equatorial bulge
of the tipped Earth and try to pull it toward the ecliptic plane.
A: Situated in the Western Cordillera of central Ecuador, the 6,31 O-metre summit of the extinct Chimborazo volcano is not only the country's highest mountain but due to the equatorial bulge
is the farthest point from the centre of the Earth
Scientists have found that the spectrum for a perfectly spherical earth is split by the planet's equatorial bulge
from the earth's rotation, the uneven distribution of continents and oceans and structures in the mantle.
Gravitational torques from the Sun and Moon on the Earth's equatorial bulge
make our planet's axis precess about the orbital plane with a period of 26,000 years.
Meanwhile, a group of researchers led by Thomas Herring at Harvard University has used VLBI data to measure a different kind of motion of the spin axis, one that changes relative to the rest of space and is driven by the sun's and moon's gravitational fields acting on the earth's equatorial bulge
. Based on the VLBI data, Herring's group has concluded in a paper recently submitted to the JOURNAL OF GEOPHYSICAL RESEARCH that the coupling between the earth's core and mantle is much stronger than predicted by current geophysical models of the earth.
In exactly the same manner, the spinning Earth slowly precesses because of the force that the tidal gravitational tugs of the Moon and Sun apply to the Earth's slight equatorial bulge
- which is tilted with respect to the ecliptic.
Tidal forces created by the star's misaligned equatorial bulges
tend to shift the orbit's long axis the opposite way from where it would normally move.