Tag Archives: Galileo

Man-made moons

Okay, remember back when we talked about how Galileo thought that we could use the moons of Jupiter as a clock, and their location would help us find our location on Earth? Or how about when Nevil Maskelyne figured we could use the positions of the stars and planets to find out where we are—if we know what time it is?

Maskelyne put in a ton of night-time hours charting the courses of the stars and planets. How much easier it would have been if the heavenly bodies just told him where they are. Well, guess what? Right now, as you sit there eating your frooty kibble, there are over 19,000 moons—man-made satellites—orbiting the Earth that we shot up into space. Every last one of ‘em sends back a constant signal telling us where exactly it is, and the time.


This site shows you where every satellite is right now—https://maps.esri.com/rc/sat2/index.html
Quickie overview of satellites for kids with a charming young lady and a puppet constructed 10 minutes before showtime—https://www.youtube.com/watch?v=03pZdYVacaM

Turn that sandglass, ye lubber!

If having a different Prime Meridian on every map weren’t enough of a headache, ocean-going navigators had to deal with another problem: clocks that didn’t keep accurate time on the bounding waves. Galileo’s clock was a bust on the ocean because the ship’s movement kept spoiling the swing of the pendulum—so the clock kept stopping. Ferdinand Magellan used sandglasses to keep time and made sure there were 18 of them on each of his ships. Sandglasses were still the most reliable timekeeper aboard a ship. Somebody had to be in charge of turning the sandglasses to keep Prime Meridian time. They probably made the littlest sailor do it—who was also in charge of taking out the trash and pulling weeds.

Why is time so important? Because longitude is time converted into degrees. To know your location you must know 2 times: what time it is where you are and what time it is at the Prime Meridian. If you don’t know both those times, you’re lost.

Back to the beginning of The Western Civ User’s Guide to Time & Space

Heliocentric blasphemy!

“We can’t torquemada heliocentrism; we can’t torquemada Copernicism; we can’t torquemada anything!”

We learned about how Aristotle and Ptolemy promoted the idea that the Earth is the center of the universe; she doesn’t move; all the planets and stars revolve around her. This is called geocentrism.

Copernicus had questions: if the planets and stars revolve around the Earth, howcome their orbits aren’t all perfect circles? He proposed that the Sun is the center of the universe and the planets and stars revolve around him. This is called heliocentrism.

When Galileo, with his newly-built telescope, observed moons revolving around Jupiter he could plainly see that not every heavenly body revolved around the Earth. Copernicus was right—at least Jupiter’s moons revolve around Jupiter. If Jupiter’s moons weren’t geocentric, how much else of the universe wasn’t geocentric?

This is the scientific method that is Galileo’s gift to us. He observed and asked questions and looked for proof.

Galileo was a brilliant self-promoter and made friends in high places. Nevertheless, his assertion that Aristotle was wrong got him in trouble with the Catholic Church. It’s not really clear to me what it was exactly that got him in hot water. Yes, there’s a passage in the Bible about the moon and Sun standing still (Joshua 10:13), but so what? The moon and Sun could still appear to stand still in a heliocentric universe.

It may be as simple as: Protestantism was still fresh; Christians were reading and interpreting the Bible for themselves (before moveable type only the priests had copies of the Bible); the Catholic Church’s establishment saw its power being challenged. Then Galileo came along and said everything you believe about God’s creation isn’t so. That may have been enough to cheese off the Church and put Galileo in front of the Inquisition.

Galileo did himself no favors when he published a fictional argument between 3 guys—to explain and prove his thesis—and made the guy with the pope’s point of view the moron. The upshot was heliocentrism was found to be heretical (against biblical belief) and Galileo was told never again to publish his heliocentric blasphemy. He was put under house arrest for the rest of his life.

It’s easy nowadays to paint the Church as the anti-science bad guy. This was indeed an embarrassing day for Christianity. If you look at the entire history of the Church, though, she’s done way more to encourage science and learning than to suppress it. Going back to Charlemagne, monasteries were the place you went to find books by classical thinkers, painstakingly translated into Latin by the monks. Most universities were originally Christian institutions. Anyhoo, a more recent pope finally admitted—after all these centuries—Galileo was right (thanks for linking this, Chuck Dillon!).


Back to the beginning of The Western Civ User’s Guide to Time & Space


Who needs a GPS?

Here’s something fun: a chart of Jupiter’s moons, showing where they will be on today’s date according to your location. Of course, Galileo proposed finding your location by observing Jupiter’s moons: you find their positions and note your local time. Those 2 bits of information are enough to tell where you are on Earth.

Here’s where you can get an app for observing Jupiter’s moons. https://skyandtelescope.org/observing/jupiters-moons-javascript-utility/

Here’s an animated chart you can download: http://shallowsky.com/galilean/

Let me see what moons are like on Jupiter

The moons of Jupiter travel around her at a regular rate, like the hands of a clock. Galileo thought that you could use the moons as a universal clock. With that clock as a reference point, you could use local time to figure out where you are on Earth.

This sounds like a great idea, but how does it work? I’m guessing that you look at Jupiter, see where her moons are, and calculate where you are on Earth based on which moons you can see. For instance, on Wednesday, May 25, if you’re in North America and you have a telescope you can watch Io and Europa pass in front of Jupiter. If you live on the east coast you’ll see them only starting out; on the west coast you’ll see them only at the end. If you live in the middle of North America you’ll see most of the passage.

Since they know exactly when those moons will be zipping across the face of Jupiter and how long it will take, astronomers are able to make charts of the moons’ progress showing local times everywhere on Earth.

This strikes me as a huge amount of work to figure out where you are on Earth. Then again, I’m holding a cell phone with a GPS (Global Positioning System) so it’s pretty easy for me to know exactly where I am. If I were floating around in the ocean in the 1600s, with no GPS, I imagine I’d be pretty desperate to know exactly where I were and would consider breaking out the old telescope to have a squint at Jupiter and her moons.


Back to the beginning of The Western Civ User’s Guide to Time & Space

Guest Blogger: Ms Physics

Diana invited me to present to her students a few years ago—a fun bunch of kids!

I’ve been pals with Diana Eline since high school. She always had more brains than I do. Diana teaches high school physics. After chatting about Galileo, I asked her to contribute some thoughts to this blog. Diana was kind enough to call together an emergency meeting of the Physics Nerds Society. Here’s what she has to say:

Galileo Galilei was born in Pisa in 1564, the first of six children of Vincenzo Galilei, a musician and scholar. In 1581 he entered the University of Pisa at age 16 to study medicine, but was soon sidetracked by mathematics. He left without finishing his degree (yes, Galileo was a college dropout!). In 1583 he made his first important discovery, describing the rules that govern the motion of pendulums.

First of all, as I tell my students, that dude Aristotle screwed up science for a long time by saying all matter is composed of Earth, Water, Air or Fire. As Aristotle was such an acclaimed philosopher no one dared to disagree with him except Galileo. Aristotle also said that heavier objects fall faster to the earth than lighter objects. Which, we of course know that it is not true. In a vacuum all objects fall to the earth at an acceleration of 9.81 meters/second squared. Only due to air resistance (air is actually composed of matter—namely gas molecules—78% nitrogen and 21% oxygen) which slows down objects with a large surface-area-to-mass ratio. Galileo also discovered many stars in the Milky way. He invented the pendulum clock. He discovered Jupiter’s moons. Although he did not invent the telescope he was the first to use it systematically to observe celestial objects and record his discoveries. His book, Sidereus Nuncius or The Starry Messenger was first published in 1610 and made him famous.

Galileo thought that a ball, rolling or sliding down a hill without friction, would run up to the same height on an opposite hill. Galileo’s conclusion from this thought experiment was that no force is needed to keep an object moving with constant velocity, which led to Newton’s 3 Laws of Physics!

Galileo Galilei is considered the father of modern science and made major contributions to the fields of physics, astronomy, cosmology, mathematics and philosophy. His flair for self-promotion earned him powerful friends among Italy’s ruling elite and enemies among the Catholic Church’s leaders. Galileo’s advocacy of a heliocentric universe brought him before religious authorities in 1616 and again in 1633, when he was forced to recant and placed under house arrest for the rest of his life.

Long story short, my enthusiasm for Physics has led my oldest son to pursue a PhD in Astrophysics and continue as an underpaid scientist!

Back to the beginning of The Western Civ User’s Guide to Time & Space