Astronomers use the principle of parallax to measure distances to the closer stars. Here, the term parallax is the semi-angle of inclination between two sight-lines to the star, as observed when the Earth is on opposite sides of the Sun in its orbit.
Ernest Rutherford discovered that atoms contain mostly empty space, with his gold foil experiment. Bhor discovered that the electrons are not randomly placed around the nucleu â¦ s.
Most of an atom's mass is in the nucleus. Rutherford: He conducted the gold foil experiment. Rutherford: There is a small, dense, positively charged nucleus. Rutherford: His model had electrons surrounding the nucleus at a distance. Rutherford: Atoms contain mostly empty space. Rutherford: Electrons travel in certain paths, or energy levels. Bohr