Looking Further

In 1609 Galileo began using a new kind of instrument that magnified distant objects: a telescope. When he trained it on the heavens, he saw countless stars and other faint objects never before seen. Suddenly, the Universe was no longer limited to what the naked eye could see. As telescopes improved, astronomers continued to push back the boundaries of the known Universe, peering ever deeper into the surrounding sea of stars known as the Milky Way.

By the late 1800s, photography was changing the way astronomers studied the Universe. The telescope had become a high-powered camera that recorded images of objects on photographic plates. These images were more accurate than hand drawings and revealed objects and details far too faint for the eye to detect. Astronomers would soon discover that the Milky Way was only one of countless galaxies, each one a vast swirl of stars.

While astronomers were starting to use photography to capture light from celestial objects, they were also learning how to analyze light itself. They found that an object's spectrum, the rainbow of colors that forms when light passes through a prism, could tell them what the object was made of and how it moved. By the late 1920s the use of spectroscopy, creating and studying spectra, produced an amazing discovery: the Universe of galaxies was expanding.