How Orbits Work


Since Aristotle’s time over 2000 years ago, we have accepted that the moon orbits the Earth. We didn’t always know why, and we didn’t always accept this for the right reasons.

We used to assume that it happened just because we saw the moon move across the sky, and we believed the Earth to be the center of all motion in the solar system. But even when we realized—in the 1540s CE—that the sun was in fact the center of the solar system, the moon kept its place around the Earth.

And rightfully so. Astronomers now know that the moon orbits the Earth based on scientific observation, rather than the “logical” guesses of Aristotle’s time. And we even know why it orbits—gravity, the one force in all the universe we can’t escape.

But I can tell you, the moon’s orbit isn’t a perfect circle, and if gravity were the only reason it orbited, it would crash straight into the Earth. After all, people stay grounded on Earth’s surface because of gravity, and we don’t orbit our planet, do we?

So how does the moon orbit the Earth? For that matter, how does any satellite? Continue reading

Newton and Gravity

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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

Johannes Kepler and Planetary Motion


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

The Copernican Revolution


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 Eclipse Seasons

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There can be no doubt that solar and lunar eclipses are some of the most fascinating sights for the “naked” eye. (And I say “naked” under the assumption that you know never to look directly at the sun without approved protection!)

Unless it’s during totality. Then you can take those glasses off.

But what I mean is, solar and lunar eclipses don’t require telescopes or binoculars to be seen. You don’t need to use any special equipment. You just need your eyes, and in the case of a solar eclipse, some form of protection—like solar glasses.

You may have noticed that when a solar eclipse comes up—or even a lunar eclipse—it’s all the rage. Suddenly, the media is swamped with safety warnings and calendar countdowns to the big event.

The United States just about lost its mind over the solar eclipse of August 21, 2017. And I have a feeling the next total solar eclipse to pass over the US, in seven years, will be just as dramatic.

But you might also be wondering…how do we know when these incredible sights are going to happen? Continue reading

Lunar Phases and Motion


The lunar phases…who really understands ’em?

We see them all the time. When we look up at the moon in the sky, we’re bound to notice that it looks just a little bit different from the last time we saw it. It changes from a slivery crescent to a full circle, and then wanes back to the crescent phase again.

The moon has behaved the same way in the sky for billions of years, ever since a Mars-sized space rock collided with the newborn Earth and the debris collected into our own personal satellite.

For that long, the moon has watched over us and captivated scientists and amateur skywatchers alike.

But what are the secrets behind its monthly changes? Continue reading

Orbit and Climate


You have probably all heard of ice ages.

v1.bjsxMTYxNDc0O2o7MTc0NzM7MTIwMDsyNTAwOzE1MDA.jpgAnd no, I don’t mean the Ice Age movies…

Although, Ice Age is actually a pretty good example of what happens during a real-life ice age. I haven’t seen enough of the movies to really talk about how accurate they are, but I know there’s a lot of ice.

And a lot of breaking of ice.

These movies take place during a time when much of the northern and southern regions of the Earth were covered in glaciers. The world looked a lot like the satellite image up above. Whether mammoths and smilodons (sabre-toothed cats) actually lived then is another question entirely.

For the record, dinosaurs were definitely not still alive back then. Even deep under the ice. The quote from the third movie basically sums it up:

“I thought those guys were extinct!”

“Then that is one angry fossil…”

Yeah, they were extinct. But fiction can do whatever it wants.

But why do ice ages happen…and why isn’t the world covered in glaciers now? Continue reading