Each of the three phases relates to the position of the sun below the horizon.
Civil Twilight - (when the sun is between 0 and 6 degrees below the horizon)
Nautical Twilight - (when the sun is between 6 and 12 degrees below the horizon)
Astronomical Twilight - (when the sun is between 12 and 18 degrees below the horizon)
Since it's pretty hard to tell sun angles when you can't even see the sun, here are a few pictures to demonstrate...
|Melbourne Sunset - 13/02/13 8:14pm (f5.6, 1/200s)|
|Melbourne sunset - 14/03/12 7:41pm (f1.8, 1/1000s)|
|Melbourne sunset - 14/03/11 7:49pm (f1.8, 1/400s)|
|Paris during twilight - 14/07/11 10:07pm (f2.0, 1/60s)|
Also, something to be aware of, sunset was at 9:50pm, so during summer in Europe there's a lot of twilight (and if you go far enough north, no technical night at all!).
|Chinchilla twilight - 24/01/15 7:32pm (f4.0, 1/3s, ISO3200)|
|Devils Marbles - 08/05/09 7:49pm (f5.6, 1.6s, ISO1600)|
|Devils Marbles -(as for image above but lightened with software and has visible noise).|
|Chinchilla - 24/01/15 - 10:32pm (f4.0, 30s, ISO3200)|
So there you have it, a photographic demonstration of the three phases of twilight. The next step is determining when each phase actually occurs. For that, I use two main resources:
- 'time and date.com' - as well as including the times for twilight phases for most major locations around the world, this site also includes times on moon phases and sun angles.
- 'suncalc.net' - this one is really funky, it's basically googlemaps with the position of the sun displayed. Any point on the globe, any date and time. This one won't tell you the angle, but it will show you. I've used this both as a photographic resource and for planning the backyard. It's very cool (but that could be the geek in me).
|Uluru and Kata Tjuta during sunrise|
Disclaimer: Tips provided on this blog are based on my own experience and research and anything I know you could probably discover yourself. These posts are written in the hope they are useful...though I make no promises.