What Galileo Saw With His Telescope

It is the summer of 1609. Mathematics professor Galileo Galilei is building his own version of an extraordinary new invention. It is the telescope, a name that means far-seeing in ancient Greek. The invention has spread like wildfire across Europe from a small town in Holland. Spectacle makers, working on the most precise glass lenses of the day, discovered that two different types of lenses held at just the right distance produce a surprising optical effect. They act like a magnifying glass for distant objects. This is the birth of the telescope. Galileo immediately sees the potential of the invention. Galileo is a practical mathematician. That's his trade. He designs instruments, he teaches the use of these instruments, and these instruments are often used for warfare. Galileo works out how to increase the magnifying power of the telescope to eight times what our naked eyes can see, and he hits on a military use for it. And it would be particularly advantageous if you could see the enemy before he can see you. The Venetian military buys this new device as a spyglass for spotting enemy ships. But then, Galileo turns his telescope from the Earth to the sky and starts a revolution. By turning the telescope to the heavens, Galileo enters a whole new regime of practice there where this instrument can be used to discover things we didn't know before about the world. All astronomers knew of the heavens before Galileo was what they could see with the naked eye, the stars and the moon. But today, even amateur astronomers can see much, much more. Alexandra Hall spends her nights gazing up at the night sky from her backyard. I never get bored of looking at the night sky above our heads. It's like 2,000 diamonds sprinkled across black velvet. And then the moon arises, and watching the moon go through its phases, I mean, it looks different every time you look at it. To the naked eye, five stars sometimes appear brighter than the rest, and watched over the course of nights, they seem to move against the backdrop of the other stars. And they don't just stay in the same place like all the rest of the stars. They move around. Sometimes they're visible, sometimes they're not. Each of these bright stars is a planet, a name that simply means wanderer in Greek. Venus, the evening star, skims the horizon at sunset. Mars glows red. Jupiter and Saturn outshine everything around them. We now know that these wandering stars are actually other worlds, like the Earth, planets as we understand them today. But in Galileo's time, everyone believes they are just stars. There is only one world in the universe, our Earth, and it sits at the very center of everything. The sun appears to circle the Earth during the day, and over the long course of the night, the moon and stars also appear to rotate across the heavens, circling the Earth in giant orbits. When you stand outside, even just for a few hours at night, you suddenly notice that all the stars and the planets and the moon, everything is wheeling around your head. It's like you're at the center of things. Really quite a powerful feeling. But Galileo is about to show that this is just a feeling. He starts to shake the known world order when he looks at the moon. The belief in his day was that all the heavenly bodies were flawless. In the old cosmology, the moon was a heavenly body and therefore perfect. But looking across a quarter of a million miles of space, Galileo sees something very different from the smooth sphere he expects. He sees instead a moon scarred with craters and valleys. It must have been an extraordinary moment for Galileo to peer with his little itty-bitty, crummy telescope at the moon and see craters, mountain ridges, valleys. He saw for the first time geographical terrain on another astronomical object. This means our Earth is not unique in the cosmos. These patches that you see are mountains, so the moon isn't smooth. It's like the Earth. But this is just the beginning. Next, Galileo turns his telescope on Jupiter, one of the wandering stars. He sees it as no one has ever seen it before. This is an exact computer reconstruction of what Jupiter looked like through Galileo's telescope. Calibrated on Galileo's actual lenses, it shows what a challenge he faced. A replica of his telescope reveals how hard it is to get a still image. Well, when I actually got Jupiter in the telescope, it was really difficult to focus because the lens quality is not very good compared to the lenses that we would get today. To the naked eye, Jupiter looks like a bright star, a spot of light. Seen through Galileo's telescope, all other stars remain as spots of light. But Jupiter suddenly appears as a much larger round disk. This blurry, shaky view of Jupiter is a revelation. Galileo comes to an extraordinary conclusion. Jupiter must be a sphere, another world, a planet as we understand it today. And around it are even more surprises. Picture yourself. You've just glued a little piece of glass on the front of a long tube, and to your utter surprise, you see two or three or maybe even four stars next to Jupiter, like little ducklings following a duck. Night after night, Galileo notes the changing position of these new stars. Imagine your surprise. Why should stars be following Jupiter? And of course, Galileo learned only after a week or two of watching those little ducklings following their mother that those, in fact, were moons orbiting Jupiter. Galileo knows he has something spectacular on his hands. He publishes his findings in a book called The Starry Messenger. It is the most explosive scientific book ever written. Its impact was immediate. Galileo became a superstar overnight. But the biggest revelation is yet to come. Galileo is recording something that will change our view of the universe forever. He observes the planet Venus changing shape and size over a period of months. As Galileo watches, Venus transforms week after week from a large crescent to a small round disk. Then shadows creep again across the planet, returning to a large crescent. To Galileo, the pattern of shadows he sees on Venus can only mean one thing. Venus is going around the sun. But the belief at the time was that everything circled the Earth. Earth is no longer the center of the cosmos. And so it said to us, wow, we're not at the center of the universe anymore. These very simple observations literally rock the foundations of the world. No longer is the Earth the center of the universe. The sun is the center of the universe, despite what our ordinary senses tell us. But these discoveries famously bring Galileo into direct conflict with the Roman Catholic Church. The Church taught that God placed mankind on Earth at the very center of creation. Defending a sun-centered universe, Galileo was actually challenging the authority of the Church. He was contradicting what was considered as the legitimate interpretation of the Bible. And the Church couldn't tolerate this. But what Galileo saw is the solar system we understand today. The discoveries that Galileo made, they changed the world forever. The world of science, the relationship between science and religion, and the universe forever. This is the universe Galileo helps reveal. Planets and their moons orbiting the sun. Telescopes today now reveal this solar system in detail that Galileo could only dream of. Explosions on the surface of the sun contain the power of a billion megatons of TNT. Features in the great red spot on Jupiter, a vast stormy vortex large enough to swallow three Earths. On Jupiter's moon, Io, we can watch volcanoes spew ash and gas high into space. On Mars, a canyon five times deeper than the Grand Canyon, and a volcano three times higher than Everest. On the surface of Venus, beneath roiling clouds of sulfuric acid, mountains rise from the rocky surface. And circling the sun at the very perimeters of our solar system, dwarf planets made of rock and ice. But one planet remains an enduring mystery for even the most advanced telescopes. Saturn and its enigmatic rings. Galileo was the first to see that this planet was different from the rest. For him, the strange features he observed looked like ears. He presumed they were moons. Later astronomers saw them as a vast flat ring encircling the planet. Then, one man discovered that this ring was in fact made up of several concentric rings. That man was astronomer Giovanni Cassini.