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

What is Precession?


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 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