Kepler saw his supernova in the year 1604. Four years later, an eyeglass-maker living in Holland, Hans Lippershey (1570-1619), put two lenses on the ends of a tube, making a device which made distant objects look larger. In 1609, Galileo Galilei built his own, improved telescope, which he offered to the city leaders of Venice, saying it could be used to spot ships at sea. The Venetians, pleased that they could see incoming merchant vessels two hours ahead of their competition (and therefore get a jump on the market) gave Galileo a considerable pay raise. By the end of that year, however, Galileo had shifted his attention to grander sights, aiming his instrument at the sky. He published his observations in the short book Siderius Nuncius, Latin for The Starry Messenger.
Galileo's book blasted the old view of the Universe apart. He described spots of light he had seen moving around the planet Jupiter. The telescope made it clear that they were Jupiter's moons, circling the planet the way Earth orbits the Sun and our Moon orbits the Earth. Furthermore, his telescope revealed that Venus goes through phases just like the Moon does, sometimes showing a thin crescent and at other times a complete disk. Galileo concluded that he was seeing the planet illuminated differently as it traveled around the Sun, one more piece of evidence that Copernicus had been right and Aristotle wrong.
Few people can have the opportunity Galileo had. Anywhere he pointed his telescope, he made a new discovery. To balance this luck, perhaps, Galileo's support of Copernicus landed him in trouble with the Inquisition, and the Catholic Church eventually placed him under house arrest. Even more galling, though, is the thought of the discovery he missed, by just a few short years. Had Galileo owned his telescope six years before, he could have observed Kepler's supernova, the bright star of 1604. He might not have spotted it sooner (with a telescope, small areas of the sky look big, so picking the right place to look can be a challenge), but he could have observed it long after it was too dim for the naked eye to see.
For many years after this, viewing objects with a telescope was the primary source of discovering new things in the cosmos. Still to this day it remains a great way to find new things in the universe and get amazing pictures like these. More recently other major advances have become more effective methods of making discoveries such as using different electromagnetic wave signatures like radio, X-ray, infrared, and gamma rays. Every method has its own set of pros and cons, so as such there are many different observatories using different types of "telescopes" to look into the vast emptiness of the cosmos.
The Great Debate Harlow Shapely (1885-1972) vs. Heber Curtis (1872-1942).
Researched, written and maintained by Blake Stacey.