once every 150 years. So it really is a once-in-a-lifetime event.
Within a day of hearing this celestial triple from Dau.II, we had Dau.I visiting and she shared that there are three sorts of twilight. We three must love each other very much. My lightning-quick response to the Twilight Triple was "I thought there were four books in the trilogy". That drew deserved cries of "lame" and a slow hand clap. That's the thanks you get for trying to be down with the popular culture of post-teenage girls. So back to the evening and the morning. As you know, I recently benefited from the existence of fading light to locate sheep troughs in a dark field at least 3 km from the nearest street light. aNNyway, the facts:
- Civil twilight is when the sun has gone from direct view but you can still see everything clear enough not to require artificial illumination.
- Nautical twilight is when sailors can still make out the horizon; and any horizon-breaking islands; but there is enough light-loss for them to be able to see the key bright navigational stars
- Astronomical twilight is dark enough for star-gazers to see pretty much all they get their telescopes out for. It is affected by street-lamp light pollution and moonshine, of course, but is effectively the same as full dark.