Most remarkably, Horrocks correctly asserted that Jupiter was accelerating in its orbit while Saturn was slowing and interpreted this as due to mutual gravitational interaction, thereby demonstrating that gravity's actions were not limited to the Earth, Sun, and Moon.

[4] His early death and the chaos of the English Civil War nearly caused the loss to science of his treatise on the transit, Venus in sole visa; but for this and his other work he is acknowledged as one of the founding fathers of British astronomy.

[5] His father James had moved to Toxteth Park to be apprenticed to Thomas Aspinwall, a watchmaker, and subsequently married his master's daughter Mary.

[6] For their unorthodox beliefs the Puritans were excluded from public office, which tended to push them towards other callings; by 1600 the Aspinwalls had become a successful family of watchmakers.

At that time he was one of only a few at Cambridge to accept Copernicus's revolutionary heliocentric theory, and he studied the works of Johannes Kepler, Tycho Brahe and others.

[10] Marston suggests that he may have needed to defer the extra cost this entailed until he was employed,[2] whilst Aughton speculates that he may have failed his exams due to concentrating too much on his own interests, or that he did not want to take Anglican orders, and so a degree was of limited use to him.

[11] Now committed to the study of astronomy, Horrocks began to collect astronomical books and equipment; by 1638 he owned the best telescope he could find.

[12] Horrocks owned a three-foot radius astronomicus – a cross staff with movable sights used to measure the angle between two stars – but by January 1637 he had reached the limitations of this instrument and so built a larger and higher precision version.

He supported his theories by analogy to the motions of a conical pendulum, noting that after a plumb bob was drawn back and released it followed an elliptical path, and that its major axis rotated in the direction of revolution as did the apsides of the Moon's orbit.

In the final months of his life Horrocks made detailed studies of tides in attempting to explain the nature of lunar causation of tidal movements.

Horrocks' observations allowed him to make a well-informed guess as to the size of Venus—previously thought to be larger and closer to Earth—and to estimate the distance between the Earth and the Sun, now known as the astronomical unit (AU).

When speaking of the century separating Venusian transits, he rhapsodised: It was a time of great uncertainty in astronomy, when the world's astronomers could not agree amongst themselves and theologians fulminated against claims that contradicted Scripture.

[27] In 2011, a sculpture by Andy Plant, titled Heaven and Earth, was installed at the Pier Head in Liverpool to celebrate Horrocks's work on the transit of Venus.