The development (and fixing and printing) of astrophotography replaced drawings for most extrasolar astronomical depiction of the sky. Illustration became the drawing of diagrams rather than pictures. The Hertzsprung-Russell (H-R) diagram, a plot of the temperature and luminosity of stars, is one of the best examples of this.

This is the very first Hertzsprung-Russell diagram ever drawn. One could say it's actually a Hertzsprung diagram, since it was drawn before Russell independently came up with the concept.

Below are two recent H-R diagrams. The first shows the stars nearby, while the second colorfully illustrates types of stars.

The H-R diagram served two purposes. First, it gave insight. This was an entirely new way to look at stars, and it laid the groundwork for modern stellar physics and evolution. Now, it illustrates the classes of stars and their evolution in a way that no mere words could match.

Ejnar Hertzsprung by Erling Poulsen, The Round Tower, Copenhagen

The Hertzsprung-Russell Diagram from Gene Smith's Astronomy Tutorial at the University of California, San Diego.