Transcript:

So, did you know that there are phases of twilight? So, the first phase of twilight is called civil twilight. So civil twilight is when the sun goes below the horizon, up to about 6 degrees. So when the sun is about 6 degrees below the horizon, that twilight is called civil twilight. 

The next twilight is called nautical twilight. Nautical twilight is when the sun is below the horizon, between 6 to 12 degrees. And when the sky is dark, as nautical twilight sets in, suddenly, the moon can pop up. Some bright stars can pop up over the horizon. Some planets even can pop up. But it depends on the location, the brightness, and how dark the sky is. 

And then astronomical twilight is when the sun is below the horizon, from 12 to 18 degrees. And at that point, the sky is dark, and you can actually see the stars. Twilight, as one astronomer put it, is the point at which the universe starts to reveal itself to us, and astronomers look forward to twilight. Pretty interesting.