While Jupiter having moons is what most people remember from what they learned of Galileo, the observations of Venus were the ones that actually changed the way that we look at the world. Not only does Venus have phases… but the planet dramatically changes in size over the course of them. You can see this for yourself with binoculars or a small telescope.
For more details on the process, including some very nifty diagrams that show how that picture proves it, wander over to science blogs.
Ars Technica has a great article on the history of the telescope. But there was something entirely non astronomy related that struck me:
In 1608, Hans Lipperhey in the Netherlands applied for a patent on a pair of lenses, one with a much shorter focal length than the other, arranged in a tube. He called it a “spyglass” as it allowed the observation of greatly distant events from a secluded retreat—Lipperhey noted that counting coins from afar was a suitable use. The patent was denied because the device was so very easily constructed.
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The big breakthrough came when Galileo was informed of Lipperhey’s failure to secure a patent. He was certainly aware of the Venetian prowess in lens grinding, as well as work in optics that Kepler had done. Galileo decided to make such a device for himself, inspired by a mixture of Renaissance gung-ho and a desire to make his name. Presumably, he reasoned that a device able to magnify distant objects would also minimize the uncertainty in their position, providing an improved version of the wall quadrant.
That’s a frightening thought, and one I hadn’t known before. Had that patent been granted, we may never have had the revolution in science in 1609, because Galileo wouldn’t have jumped into the telescope manufacturing business. That work is what sealed the fate of the geocentric solar system, and became a great leap forward for all physical sciences.
When I found out that this weekend was the closing weekend for the Galileo exhibit at the Franklin Institute, I made some quick plans to go down and see it. The exhibit was about the age of science and discovery at that time (400 years ago), with the center piece being 1 of the 2 surviving telescopes that Galileo made. No pictures were allowed, but I found this one on the internet which must have been done as part of a press bit.
That’s it. That wooden tube with a lens no larger than a quarter (and even a smaller aperture) is what discovered the moon wasn’t a perfect sphere, and that Jupiter had moons. The publishing of those discoveries put the nail in the coffin of the heliocentric theory of the universe, and started to open our eyes to the wonders of what is out there.
As you can see, they set up the case so you can look through the telescope yourself. You aren’t getting anywhere near the focal plane, so you can just see a bit of light, but it is still something to be able to look through the same lenses that created such a scientific revolution. Later in the exhibit they had telescopes that had recreated lenses, and light projections of Jupiter and Saturn on a wall, so you could see what it looked like.
We stayed in the exhibit for 2 full hours. I must have spent nearly 30 minutes milling around the telescope itself, chatting with, and listening to Frank, the museum staff that was manning the exhibit and telling great stories of it. I hadn’t realized how much of an entrepreneur Galileo was, much like Ben Franklin. After his discoveries, he got into the telescope making business, as owning a telescope (whether or not you knew how to use it) became high fashion for nobles of the day. I also found out that our president made a point to come to the exhibit and see the telescope, which I appreciated.
One last thing that Frank said really stuck with me. The telescope is insured for 7 million dollars. But he said “a dollar or a billion dollar’s, what’s the difference. Once this is gone it can’t be replaced.” The fact that the Italian government has managed to preserve 2 of Galileo’s telescopes for 400 years is a truly impressive feat.
The exhibit closes on Monday, and the telescope goes back to Italy. It was only allowed to leave the country for this special International Year of Astronomy exhibit at the Franklin. I’m very happy that we took the time to get down there, images of that telescope will be burned into my brain for a very long time.
It's always more complicated 