Tag Archives: science

The Tropics

Here’s something interesting: the Tropic of Cancer and the Tropic of Capricorn don’t stay put. They move around a little bit. The Tropic of Cancer marks where the Sun will shine the longest in the northern hemisphere for this year—that is, the summer solstice. It’s at around 23-24 degrees north. On the summer solstice, June 21st-ish, the Sun will shine directly over the Tropic of Cancer.

The Tropic of Capricorn marks where the Sun will shine the longest in the southern hemisphere—that is, the winter solstice. It’s at around 23-24 degrees south. On the winter solstice, December 21st-ish, the Sun will shine directly over the Tropic of Capricorn.


Here’s kind of what they look like on a flat map.

The reason the Sun shines directly on the Tropic of Cancer in summer and the Tropic of Capricorn in winter is that our Earth is tilted as she revolves around the Sun. We learned that way back when we read about Eratosthanes.

It takes one year for Earth to orbit the Sun. When the Northern Hemisphere is tilted toward the Sun it’s Summer there. When the Southern Hemisphere is tilted toward the Sun it’s Summer there.

Latitude and Longitude

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


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


Next up in our continuing series of Old Dead White Guys is Galileo, who lived from ad 1564 – 1642 in Pisa, Italy. He was a scientist whose method was to prove or disprove an idea by conducting experiments and observing the results—the way we understand science today. For instance, to prove the idea that a heavy object and a light object will fall at the same speed, he dropped a heavy weight and a light weight (like a bowling ball and a billiard ball) from the top of the Leaning Tower of Pisa. He dropped them both at the same time. They landed on the ground at the same time.

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

Happy Easter!

The Chinese invent the compass

A thin piece of magnetized iron in the shape of a fish (or a shallow boat) floats in water and points north.

The magnetic compass was invented in China sometime between the 2nd century bc and ad 1st century. They used it to make sure streets and houses aligned with the Earth in a harmonious way—what is called feng shui. The Chinese later figured out they could use a compass for finding their way on the ocean (ad 1040-44).

This carefully-balanced magnetized iron spoon points north with its handle.

How you can harness the awesome and terrible forces of the Earth’s core

We learned last post that the Earth’s core is surrounded by molten metal, which exerts a magnetic field around the planet. Some metals can be magnetized. They can be made into a magnet, so they exert a force on other metals without touching them. Iron and steel can be magnetized.

The thing about Earth’s giant magnetic field is that magnetized metals—if they can—try to line up with it. If you were to take a small piece of iron or steel (like a needle) and rub it a few times with a magnet, it will try to align itself with Earth’s North and South. You could make it easier for the needle if you float it on a piece of styrofoam or cork in a bowl of water. After the needle settles down it will point North-South. Congratulations! You built a compass.

Here’s what you’ll need: a bowl, water, a needle, a piece of cork or styrofoam, and a magnet. I got my magnet off of the refrigerator door. If you cut a slice off the cork, get someone to do it with a craft knife. Use a cutting board! Don’t cut it on your mom’s good dining room table. I don’t want angry messages in the comments section.

Rub the needle with the magnet a bunch of times.

Stick the needle halfway through the cork. It may be a good idea to put the butt-end of the needle on a cutting board and press the cork down onto it.

Fill the bowl with water and float the needle and cork in the water. After a little while the needle will point north-south.



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

Magnetic fields

Well, everybody who reads this blog called me this morning in a panic because of that last post. The post where I explained how we’re all doomed. I went to bed before going on to explain that we’re not doomed. Sorry, gang.

Probably I should have mentioned: the molten metal inside the Earth is magnetic. It behaves like a giant magnet. Magnets have 2 poles and so does Earth, thanks to its sizzlin’ hot molten metal core. If you’ve ever put a magnet on a sheet of paper and sprinkled metal filings onto it, you’ve seen the filings arrange themselves into circular patterns around both poles. These are magnetic fields.

There are gigantic magnetic fields around Earth’s north and south poles that extend way out into space. You can’t see them. You know what they do? They act like a shield against whatever dust the Sun keeps shooting at us. That’s why we’re not gasping for oxygen and wiping sun-dust off our computer screens.

Pretty neat, eh?

What is Earth’s Magnetic Field?


I add this link in the interests of science:

We’re doomed!

Here’s something you ought to know about living on planet Earth. We’re standing on a giant globe that rotates on its own axis, and also rotates around the Sun. Right where you’re standing, deep below the surface you’re standing on, it is hot enough inside the Earth to melt metal! In fact, there’s molten metal sloshing around in there RIGHT NOW! Molten metal!

While that’s going on, our pal the Sun is shooting dust at us. Yes, that’s right—solar winds are blowing enough dust to scrape the atmosphere right off Earth’s surface like sandpaper taking the skin off an apple—RIGHT NOW! No air!

I haven’t been able to sleep a wink since I found out about all this. We’re doomed!

Egyptian sundials


An Egyptian lady catching some rays from Ra.

Let’s travel west from Sumer, away from the MidEast, along the northern coast of Africa to Egypt. About 1,000 years after civilization was up and running in the Tigris-Euphrates valley, the Egyptians got started on their civilization which thrived from 3100 bc to 332 bc. Like the Sumerians, Egyptians depended on a river—the Nile—and a system of irrigation to water their crops to keep the economy going. Their writing system was hieroglyphics—symbols that represented sounds, or ideas, or things. Their government was monarchical—they had a single ruler, called a Pharaoh. The Egyptians worshiped a pantheon—which means a bunch of gods and demi-gods. The Pharaoh was worshiped as a god, too.

The Sumerian culture must have influenced the Egyptians somewhat. The Egyptians divided the day into two halves, each having 12 hours—twelve is an easy Base Sixty number. The Egyptians are thought to have invented the sundial. The earliest example of a sundial has 12 hours marked using lines on a semi-circle, 15° apart.



A fragment of a limestone sundial. The gnomon goes into the hole at top.


This sundial is a half-bowl cut out of a block of stone.

A sundial is a simple way to measure the passage of the Sun. There’s a post (called a gnomon, pronouced NOM-ON) sticking up from a flat, horizontal surface. Lines are drawn on the flat surface, radiating out from the gnomon. When the Sun is shining, the gnomon casts a shadow on the lines. Each line represents the passage of an hour.

The Egyptians built huge obelisks—big stone monuments. These were sundials, too. The obelisk cast a shadow on the ground, which was marked for every hour. As the Sun moved across the sky, the shadow would move along the dial, showing the time. Of course, sundials only work when there’s daylight. How did they tell time at night?