WEBVTT - What's the Difference Between Dusk and Twilight?

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<v Speaker 1>Welcome to brain Stuff, the production of I Heart Radio. Hey,

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<v Speaker 1>brain Stuff, Lauren fog Obam. Here. As you watch a

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<v Speaker 1>setting sun, you see the sky go darker. Some people

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<v Speaker 1>call that period dusk, while others may call it twilight.

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<v Speaker 1>But these words aren't arbitrary. In the astronomical world, they

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<v Speaker 1>have specific meanings. Astronomers have classified three types or phases

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<v Speaker 1>of twilight, dusk, and dawn, so today let's talk about

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<v Speaker 1>what they are and how you can tell them apart.

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<v Speaker 1>The three phases of twilight are civil, nautical, and astronomical twilight.

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<v Speaker 1>Civil twilight occurs when the sun is between zero and

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<v Speaker 1>six degrees below the horizon. It's the brightest phase of twilight.

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<v Speaker 1>Nautical twilight occurs when the sun is between six and

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<v Speaker 1>twelve degrees below the horizon, and astronomical twilight occurs when

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<v Speaker 1>the sun is between twelve and eighteen degrees below the horizon.

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<v Speaker 1>It's the darkest phase and occurs just before or after

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<v Speaker 1>night night, being classified as when the sun is eighteen

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<v Speaker 1>degrees or farther below the horizon. These phases of twilight

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<v Speaker 1>occur in the same order anywhere on Earth, but how

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<v Speaker 1>long they last is based on your location on Earth.

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<v Speaker 1>That's because how long each phase lasts depends on the

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<v Speaker 1>season and latitude that you're viewing the sun from. Each

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<v Speaker 1>phase of twilight can be as short as twenty four

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<v Speaker 1>minutes if you're near the equator, or last several weeks

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<v Speaker 1>if you're at or near one of the poles. During

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<v Speaker 1>the summer or winter solstice. When most people say it's twilight,

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<v Speaker 1>they're referring to civil twilight, that first phase of twilight

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<v Speaker 1>that occurs just before sunrise or just after sunset. At

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<v Speaker 1>this point, the sun is barely below the horizon and

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<v Speaker 1>there's still a good amount of light in the sky.

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<v Speaker 1>Many countries and cities that laws based on this stage

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<v Speaker 1>of twilight, such as requiring street lights and headlights on

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<v Speaker 1>cars to turn on. Unfortunately, there's no hard and faster

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<v Speaker 1>rule for telling the difference between each type of twilight

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<v Speaker 1>by eye, because after all, you can't see how far

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<v Speaker 1>below the horizon the sun is from your point of view.

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<v Speaker 1>But one technique is to determine how well you can

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<v Speaker 1>distinguish shapes in the dark. Obviously, we know that when

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<v Speaker 1>the sun breaks above or dips below the horizon, the

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<v Speaker 1>time just before or after that is civil twilight. When

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<v Speaker 1>the horizon itself becomes difficult to distinguish. That indicates that

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<v Speaker 1>you're in a nautical twilight. The term dates back to

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<v Speaker 1>mariners navigating the world by ship. After the sun dips

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<v Speaker 1>below twelve degrees, a sailor usually can't distinguish between the

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<v Speaker 1>sea and the sky. Meanwhile, when you're in astronomical twilight,

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<v Speaker 1>the darkness is almost complete, The sky is an inky black,

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<v Speaker 1>and it's hard to distinguish any shapes at all unless

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<v Speaker 1>the moon is lighting up the night. Another technique is

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<v Speaker 1>to note the stars you can see. In civil twilight,

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<v Speaker 1>only the brightest stars and visible planets can be seen.

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<v Speaker 1>It became ms increasingly easy to spot stars throughout nautical

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<v Speaker 1>twilight until astronomical twilight, when even the faintest stars and

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<v Speaker 1>sometimes even the milky Way can be seen. While we

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<v Speaker 1>often use the terms dawn, dusk, and twilight interchangeably depending

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<v Speaker 1>on the time of day, both dawn and dusk have

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<v Speaker 1>specific astronomical meanings too. A civil dusk occurs when the

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<v Speaker 1>sun is exactly six degrees below the horizon in the evening.

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<v Speaker 1>Nautical dusk occurs when the sun has twelve degrees below

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<v Speaker 1>the horizon and astronomical dusk occurs when it's eighteen degrees

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<v Speaker 1>below the horizon. Conversely, civil, nautical and astronomical dawn occur

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<v Speaker 1>when the sun is at those respective degrees below the

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<v Speaker 1>horizon before sunrise. In other words, the three types of

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<v Speaker 1>dawn and dusk are specific points. The three types of

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<v Speaker 1>twilight are the phases between those points. To get a

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<v Speaker 1>sense of how far six degree increments are in the sky,

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<v Speaker 1>you can use your hand by holding your arms straight

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<v Speaker 1>out and putting three fingers up from your closed fist.

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<v Speaker 1>The distance from one side of your fingers to the

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<v Speaker 1>other is roughly five degrees. This may help you understand

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<v Speaker 1>how far the sun might be below the horizon at

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<v Speaker 1>each phase of twilight. Today's episode is based on the

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<v Speaker 1>article what's the difference between Twilight and dust? On how

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<v Speaker 1>stuff works dot com written by Valerie Steama. Brain Stuff

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<v Speaker 1>is production of by Heart Radio and partnership with how

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<v Speaker 1>stuff works dot Com, and it's produced by Tyler Klang.

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