Astrophysics is the field of science that combines astronomical observations with physical principles. It may be argued that the first true astrophysicist was Sir Isaac Newton, who explained the orbits of the planets, which had been known from antiquity, from his laws of motion and his universal law of gravity. As a field, astrophysics first began to mature in the latter half of the nineteenth century. This was due primarily to several key technical innovations that revolutionized the field of astronomy.

First, as the nineteenth century progressed, so did the sizes of the largest telescopes, and hence the furthest distances, as well as the smallest and dimmest features astronomers could observe. Whereas earlier astronomers usually worked in relative isolation using small telescopes, increased support from both governments and private individuals led to the founding of more observatories (like the U.S. Naval Observatory in 1844, the Lowell Observatory in...