Stars and Proper Motion

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Recognize this constellation?

Well, at the time stamp of about 2000 AD (CE), I think you will. It’s one of the most famous constellations in the night sky.

Well, technically, it’s not a constellation at all.

It’s an asterism—a commonly recognized grouping of stars that isn’t actually official as a constellation. There are tons of asterisms that you no doubt recognize…the Summer Triangle, the Great Square of Pegasus, the Big Dipper.

That’s right. That mess of stars up there that keeps changing for some reason…that’s the oft-recognized Big Dipper, part of the constellation Ursa Major.

So why the heck are the stars moving? Continue reading

Distances Between Stars

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When you look up into the sky on a clear night away from the glare of the city, you see trillions upon trillions of stars.

Thousands of years ago, the classical astronomers saw the same thing you do today—except perhaps a little different, due to the ever-changing cosmos. And, like you, they weren’t satisfied with just looking. They wanted to know what was out there.

For hundreds of years, they developed model after model to explain why the stars seemed to orbit the Earth and why certain objects in the sky—which they named planetsseemed to wander backwards from time to time.

Tycho Brahe, an astronomer known mainly for what he got wrong, dismissed the idea of the Earth orbiting the sun because he could detect no parallax between the stars.

If he had been able to measure parallax, he might have realized that the universe was much larger than any of his fellow classical astronomers imagined.

So what is parallax…and how can it help us measure the distances between stars? Continue reading

How Orbits Work

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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

From Classical Beginnings

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The universe as we know it was born out of chaos.

We have a pretty good idea of the scale of our universe and how it began—as an infinitely dense point of matter that blew apart in what we call the Big Bang. That’s chaos for you, right there.

And chaos continues to define our daily lives.

Stars are born out of the complete chaos of gravity, and nothing in the universe forms gently. Our moon was born out of a violent collision with the Earth. And I’m sure you’ve noticed how easy it is to let a room get disorganized.

All these are examples of chaos—known as entropy in science. Everything tends toward chaos. But the ancient Greeks rebelled against this idea.

In their view, everything in the cosmos had to be perfect. It was a somewhat spiritual way of looking at the universe, if you think about it. And even as they developed the groundwork for science as we know it today, one idea hindered them… Continue reading

The Saros Cycle

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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

The Elusive Light Year

 

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In my last post, I showed you just how huge astronomical distances really are. There’s a reason people say that incredible things are “astronomical!”

The image above illustrates how far Earth is from the nearest star, Proxima Centauri. But what does it mean for two objects to be 4.3 light years apart?

The light year is a unit of distance, used to measure distances that escape traditional units on Earth. It’s impossible to measure the universe in kilometers or miles; many thousands fit into one planet alone.

Even “astronomical units,” the distance between the Earth and the sun, are too small. That distance, as we saw in my last post, is barely a fraction of the distances in our solar system alone.

So what exactly is a light year?

Continue reading