Reply To: Science and Astronomy in the Torah

[laws of gravitation]

1. The Sun rotates around the Earth.

2. The Earth rotates around the Sun.

This is derived on a non-inertial reference frame. From the perspective of an Earth-centered reference frame, the Sun does indeed orbit around the Earth. In General Relativity, all reference frames are equally valid.

To put it more simply, all motion is relative. Relative to humanity, the Earth is not rotating. For most of history, the Sun was said to circle the Earth. Copernicus, changed sciences viewpoint, so that Earth rotated around the Sun. Newton changed it again, and said that Earth and Sun rotate about a common center of gravity. Einstein changed it again. He described General Relativity – in which all motion is relative. In General Relativity, you can use any frame of reference. Relative to humanity, the Sun revolves around the Earth.

Yes, it is a bit harder to explain stellar parallax from the perspective of an Earth-fixed reference frame than from the perspective of a solar system barycentric reference frame.

On the other hand, it is extremely difficult to explain a cyclone from the perspective of a solar system barycentric reference frame. No meteorologist would even think of using anything other than an Earth-fixed reference frame to model the weather.

BTW, it’s not all that hard to explain stellar parallax from the perspective of an Earth-centered frame. The motion of the stars can be explained in terms of the “third body effect”. People who model the behavior of satellites in Earth orbit vastly prefer to use an “Earth-centered inertial” reference frame (a non-rotating reference frame with origin at the center of the Earth) than a barycentric frame. From the perspective of such a reference frame, the Sun and Moon (and the planets) make the satellite’s orbit not quite Keplerian. The perturbation is explained by a pseudo-force called the third body effect.