Thanks to the editor(s) for clearing up twilight vs dusk in these comments. It was very confusing reading the article because it sounded like they were saying dusk and twilight are different but still use the 18, 12 and 6 degree measurements. So, it sounded like they were the same.
If they would have stated twilight begins when the bottom of the sun first hits the horizon, and dusk begins when the sun just goes below the horizon it would have been clear.
Thanks to the editor(s) for clearing up twilight vs dusk in these comments. It was very confusing reading the article because it sounded like they were saying dusk and twilight are different but still use the 18, 12 and 6 degree measurements. So, it sounded like they were the same.
If they would have stated twilight begins when the bottom of the sun first hits the horizon, and dusk begins when the sun just goes below the horizon it would have been clear.