This transcript was edited for brevity and clarity.
Bill Burton: It's time for us to take a look at the Science Behind the Forecast as I am joined by WAVE 3 meteorologist Tawana Andrew. Good morning, Tawana.
Tawana Andrew: Good morning. Today's topic has to do with a certain time of day.
BB: Yeah, the opposite time from when people are listening to this, as we're going to be talking about twilight and its variations. What do we need to know?
TA: So twilight is defined as the time frame before sunrise or after sunset, when the atmosphere is partially illuminated by the sun. And there's actually three categories of twilight. There’s civil, nautical and astronomical.
So for civil twilight, it's also known as civil dawn or civil dusk, this occurs when the sun's geometric center is between zero and six degrees below the horizon. So this is the time frame where the sky is all those pretty colors, and you start to see a lot more of those colorful sunrises or sunsets as you're getting more of that red light, and red wavelength of light, I should say, being scattered more than the blue light.
BB: So right around sunrise or sunset, then.
TA: So the pretty colors that we always love and photographers like crave.
So the duration of civil twilight actually will vary depending on where you are and the time of year. So for the poles, for example, the sun's path only dips below the horizon at certain times of the year, and often is not even low enough for the sky to become completely dark, so you can end up in areas near the poles with twilight lasting two to three weeks. That's an incredible, incredibly long amount of time. And then in the Arctic, or the Antarctic, civil twilight can last for several hours. Now, for the equator, right along the center of the planet, civil twilight may last for 20 to 30 minutes just because the sun is more perpendicular to the horizon. So as the sun's angle changes, depending on where you are on the planet. How long civil twilight lasts also will vary.
And then there's nautical twilight, which happens when the sun's geometric center is between six degrees and 12 degrees below the horizon. It's known as nautical twilight because sailors are involved. Yes, this was a time frame that they were first able to take reliable readings of the stars while they could still see the horizon.
BB: Okay, that makes sense.
TA: So you gotta figure out where you're going right?
BB: That would be helpful.
TA: So being able to see the stars in the horizon was a perfect time frame for those first readings.
And then there's astronomical twilight, where you have the sun's geometric center between 12 degrees and 18 degrees below the horizon. To most observers, for us, just with our eyes, it looks like the sky is completely dark, but there's still just a little bit of illumination going on. And this is the point where you could start to see some stars, some planets. So astronomers love this time of night, as long as there's no light pollution to obscure what you're trying to see. And once you get past that 18 degree mark, you're fully in to night.
