Newton and Gravity

earth and moon.jpg

So, the moon stays in orbit around the Earth, right?

Yeah, I thought so. But why? The moon’s orbit is not a straight line, which means it’s accelerated motion (using the physics definition, which is absolutely any change in speed or direction).

And in order for acceleration to happen, according to Newton’s first law of motion, a force has to happen—meaning, something has to reach out, touch the moon, and drag it into orbit around Earth.

Well, that doesn’t happen, last I checked. I mean, it’s not like we have some kind of giant cord connecting us to the moon. How crazy would that be?

So why does the moon orbit the Earth? Continue reading

Newton’s Laws of Motion

Sir-Isaac-Newton-Jean-Leon-Huens.jpg

It’s said that Sir Isaac Newton was sitting under an apple tree when an apple fell on his head, and that’s when all his discoveries began.

Personally, I doubt that story—just as I doubt that Galileo Galilei ever dropped iron and wooden balls off the Leaning Tower of Pisa. His goal would have been to show that both objects hit the ground at the same time. Unfortunately, wind resistance would have gotten in the way.

Regardless of how Newton discovered gravity, his scientific achievements are monumental. In fact, we recognize him today as one of the greatest scientists to ever live, second only to the famous Albert Einstein.

Newton’s revelation that gravity draws objects toward Earth changed the course of modern science. But what exactly did he find out? Continue reading

Galileo and Motion

galileo measurable.jpg

Before Galileo’s time, Aristotle was the god of gravity.

Seriously. Before Galileo came along, the question of how gravity worked was answered with another question: “What would Aristotle say?” Obviously, this method was faulty, since Aristotle was actually wrong about most scientific things he wrote about.

But Galileo began a tradition that would persist into the modern day. He’s credited for having performed the first true science experiments when he observed falling objects.

You could, of course, call Tycho Brahe’s night sky observations and Kepler’s correct application of mathematics to the heavens true science, but neither of them really performed experimental science. That distinction lies with Galileo.

Wait a second…so I thought Isaac Newton was the guy who discovered gravity? Continue reading

Galileo and the Telescope

Galileo-Galilei-Quotes-3.jpg

When you hear the name “Galileo Galilei,” what immediately comes to mind?

If you thought, “inventor of the telescope,” you’re not alone. I also wouldn’t be surprised if you thought “condemned by the Inquisition for believing the Earth orbited the sun.”

But neither of these are true. If you’ve been following my more recent astronomy posts, you probably realize why—in Galileo’s time, people already knew that the Earth moved around the sun.

The idea that he invented the telescope is more understandable…but, again, it’s not true.

So what is true about Galileo, and how did he contribute to our understanding of astronomy? Continue reading

Johannes Kepler and Planetary Motion

Kepler.jpg

Thales and Pythagoras suggested that the natural world could be understood. Aristotle dared to imagine what was beyond the Earth. Plato encouraged thought about the universe, even if he did take astronomy one step forward and two steps backward.

Copernicus followed in Ptolemy’s wake, devising the revolutionary heliocentric (sun-centric) model of the universe. Tycho Brahe may have (incorrectly) rejected that model, but he did make some of the most detailed night sky observations yet.

What’s more, by Johannes Kepler’s time, Tycho had cast doubt on the idea of uniform circular motion that had plagued astronomy for centuries.

At last, the world was ready for a more mathematical take on a question that had confounded philosophers, mathematicians, and classical astronomers alike: how do the planets truly move through space?

By standing on the shoulders of giants, Johannes Kepler was finally able to devise his three laws of planetary motion, which are still the leading mathematical theory today. Continue reading

Tycho Brahe, the Observer

tycho-brahe-2.jpg

It is surprisingly difficult to find a flattering image of Tycho Brahe.

Honestly. Do me a favor and do a Google image search for the guy. It’ll come up with all sorts of disfigured images, mostly because his nose got messed up in a sword fight…

I know what you’re thinking. A classical astronomer in a sword fight? Suddenly these people seem less like heroes of modern-day science and more like human beings with lives of their own.

Tycho certainly fits the trend. He’s known for being quite the unpopular sort. Bad-tempered and vain, there were few who respected him for more than just his astronomical accomplishments—and even those were few.

So why is he even important, then?

Continue reading

The Copernican Revolution

Nicolas-Copernicus.jpg

Nicolaus Copernicus lived from 1473-1543, a time when rebellion against the Church was at its height. And unfortunately for the astronomy of the time, it had gotten inextricably tied up with Christian teachings.

In that time, heaven and hell weren’t just parts of our personal religions and beliefs—the Church held some of the highest authority over the land, and questioning heaven and hell just wasn’t done.

The way astronomers of the time pictured the universe fell right in sync with the heaven and hell geometry—Earth was the imperfect center of the universe, with hell nested deep below. Heaven was a place of perfection, and it was where all the heavenly bodies—the moon, sun, planets and stars—all moved.

Problem was, the Ptolemaic model of the universe really couldn’t explain detailed observations. It used epicycles to explain why the planets moved backwards sometimes. And no matter what people tried, they couldn’t get it to be accurate…

But then along came Copernicus, who would be the first to challenge the Ptolemaic universe and be believed. Continue reading

The Ptolemaic Universe

Ptolemy Retrograde Motion.jpg

Claudius Ptolemy lived about five centuries after the Greek philosopher Aristotle’s time. Aristotle’s model for the universe—the first geocentric model, with Earth at the center—was still widely accepted, and Ptolemy sought to improve it.

Ptolemy was one of the first of the ancient Greeks to be a true astronomer and mathematician, rather than a philosopher.

Where Aristotle, Plato, Thales, and Pythagoras before him had tried to use “pure thought” to understand the nature of the heavens, Ptolemy set about to perfect the geocentric model mathematically.

This was a huge step forward for science as a whole, as science today relies heavily on mathematics.

In Ptolemy’s time, science didn’t really exist yet. The Greeks preferred to just think through problems logically and reasonably, and if the logic they used was based on untrue assumptions…well, no one was the wiser.

But Ptolemy came up with the wonderful idea to line up observations of the sky with mathematics. And even though Aristotle’s view of the universe shackled him, he moved science forward with great strides. Continue reading

Archaeoastronomy

iStock_000020751712_Double.jpg

Imagine that you’re living sometime around 2000 BCE, give or take a thousand years or so. That’s about 4000 years before our time.

You look up at the sky at night, and see it filled with numerous points of light. Some of them stay mostly fixed, but move mysteriously in circles around the north pole. Others move with the rest, but wander a bit from time to time.

And then there’s the sun, whose brilliant rays light the day. The moon, like the sun, doesn’t seem to follow the path of the lights in the sky. It even changes its shape, and sometimes disappears entirely.

Wouldn’t you wonder if there was some pattern to these otherworldly motions? Wouldn’t you devote time to studying them and seeing if you could predict them? Continue reading

The Saros Cycle

solar eclipse3.jpg

Would it surprise you to hear the solar eclipses repeat?

Now, I know we can’t go back in time to see past eclipses, and once the date of an eclipse—say, March 7, 1970—has passed, that date will never come again. It’s simple reality, and we’re all aware of time’s passing.

But as you’ll soon realize through these astronomy posts, astronomy is full of repeating cycles. And one of those is the saros cycle, or simply the “saros.” It’s an eclipse prediction cycle, and after every one, the same eclipse occurs again.

But how? Continue reading