4. Sun Gazing
After passing the Tropic of Cancer, Terry recorded a phenomenon that happened on April 7th at midday:
The sun was our zenith, or vertical, at noon-day, directly over our heads; which we found by this infallible demonstration, made by a slender knife, or long needle, set upright, which did cast no shadow. The sun in this course like the equinoctial, divides the globe of the Heavens in two equal parts.
As hinted at in this passage, the 17th century was a time of incredible advances in astronomy and navigation. Although people have studied the stars and heavens for over two thousand years, it was only in the 16th and 17th centuries that astronomy became a true physical science. Due to outside developments in the fields of philosophy and theology, people began to see the stars and the heavens as occupying spaces not distinct from the earth. Accordingly, scientists began to see the effects of gravity as a force that governed how the planets moved. The work of mathematicians like Galileo and Newton helped astronomers chart the movements of the stars in the night sky, which in turn helped sailors better navigate in the open ocean. These developments naturally led to the invention of better instruments for observing celestial bodies, most notably the telescope.