什么是 Geocentric and terrestrial frames？

The geocentric frame has its origin at the Earth’s center and axes pointing to fixed stars; it is inertial to an excellent approximation for motions of a day or less (its own acceleration around the Sun is only $6 \times 10^{-3}\,\mathrm{m}/\mathrm{s}^{2}$, and nearly uniform over the Earth). The terrestrial frame, attached to the ground, rotates with respect to it about the polar axis at