The Ecliptic

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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

Precession

precessionglobes

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

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