The Ecliptic


The ecliptic, as astronomers call it, is the apparent path of the sun against the background of the stars in the sky.

It’s useful because it tells us how to find the planets in the sky. They can be hard to spot if you don’t know where to look, but they will always be somewhere along one imaginary line that arcs across the sky—the ecliptic.

This pattern never changes. The planets don’t follow the ecliptic exactly, but it’s useful for getting an idea of where they should be.

But why does it work—and what exactly does it mean, when it’s obvious we can’t see the sun among the stars of the night sky? Continue reading



We have a bit of a shorter post today—I thought precession warranted its own post, before I go on to talking about the ecliptic.

Precession is refers to the way Earth wobbles around on its axis, a bit like a top. This motion is caused by the sun and moon’s gravity tugging on the planet, and is key to understanding how many ancient cultures viewed the sky.

So what is precession, exactly? Continue reading

The Celestial Sphere


The celestial sphere is certainly a strange way to think about the night sky.

It makes sense to use globes to diagram the Earth. The Earth, after all, is a roughly spherical planet, and flat paper maps have a way of distorting distances.

The sky, though? Seriously? I mean, we all know the universe isn’t exactly a defined sphere that barely extends past Earth’s surface, right?

I mean, this model—the “celestial sphere”—even tries to claim that all the stars sit on the plane of the sphere like thumbtacks on a ceiling. And that the planets in the solar system follow regular paths around this odd-looking sphere.

Pretty strange way to think about the night sky, right?

Well…I have to say, astronomers do have a point. Continue reading

Mapping the Sky

bigI need you guys to help me with something.

Can you find a horse in this image of the night sky?

Yeah, me neither. I’m lost. I see the Great Square of Pegasus because I know what to look for, but I still don’t see a horse.


Okay, so now I see half a horse. Where’s the rest?

Your guess is as good as mine, guys. Truth is, constellations very rarely look like what they’re named after. Constellations are more like relics of our ancient past than actual descriptors of what we see up there in the sky. But they do serve a purpose, even if that horse up there is missing his back legs.

I really find myself wondering if whoever made up Pegasus was concerned with animal rights… No animals were harmed in the making of this sky map…

Okay, yeah, never mind.

Where was I? Ah, that’s right. The purpose of the constellations, and the reason why it really doesn’t matter if they don’t look like their names say they do. Continue reading

The Elusive Light Year



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

Where Are We?


In the 4th century B. C. E. (Before Common Era), scientists believed the Earth was the center of the universe. Before that, they were convinced the Earth was flat.

Now, if anyone so much as mentions that the Earth is the center of the universe, they are quickly corrected. The very idea is absurd. (Although there are in fact online “societies” for people who believe the Earth is flat.)

We now know that not only is the Earth not the center of the universe, but neither is the sun, which is undeniably the center of the solar system. Were we to zoom out much further and take a look at our galaxy, the Milky Way, we would find that the sun is not even near the center of its own galaxy.

In fact, it’s located in a small “spur” of stars just off one of the spiraling arms of the galaxy. Since the current theory states our universe is infinite, there can’t even be a center, and thus our galaxy is not the center of everything. How wrong those early astronomers were!

But what does all this mean? Where exactly are we in the universe?

Continue reading