Welcome to Brain Stuff, a production of iHeartRadio.

Hey, Brain Stuff, Lauren Vogelbaum here.

As you watch a setting sun, you see the sky go darker.

As some people call that period dusk while others may call it twilight.

But these words aren't arbitrary in the astronomical world.

They have specific meanings.

Astronomers have classified three types or phases of twilight, dusk, and dawn.

So today, let's talk about what they are and how you can tell them apart.

The three phases of twilight are civil, notical, and astronomical twilight.

Civil twilight occurs when the sun is between zero and six degrees below the horizon.

It's the brightest phase of twilight.

Notical twilight occurs when the sun is between six and twelve degrees below the horizon.

And astronomical twilight occurs when the sun is between twelve and eighteen degrees below the horizon.

It's the darkest phase and occurs just before or after night.

Night being classified as when the sun is eighteen degrees or farther below the horizon.

These phases of twilight occur in the same order anywhere on Earth,

but how long they last is based on your location on Earth.

That's because how long each phase lasts depends on the season

and latitude that you're viewing the sun from.

Each phase of twilight can be as short as 24 minutes if you're near the equator

or last several weeks if you're at or near one of the poles during the summer or winter solstice.

When most people say it's twilight, they're referring to civil twilight.

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