Post by jim on Sept 1, 2021 16:54:32 GMT -5
The Three Twilights
When you see my light data posts you notice I use the terms Begin Morning Nautical Twilight (BMNT) and End Evening Nautical Twilight (EENT).
There are three twilights - Astronomical, Nautical and Civil.
Astronomical Twilight is the darkest of the three twilights and is when the suns geometric center is 18 to 12 degrees below the horizon. The stars are beginning to fade as the sky gets lighter but the ground is still dark.
Nautical Twilight is when the sun's center is 12 to 6 degrees below the horizon. During nautical twilight objects on the ground can be seen and you can begin to walk somewhat quietly without tripping over a tree stump.
Civil Twilight is when the sun's center is 6 degrees up to sun rise. It is light enough to carry out most outdoor activities.
Nautical Twilight is the one we're interested in for a number of reasons. 1st, when showing up at an event Friday evening you'll know what the light conditions will be when you show up. Get there after EENT and you'll be driving into a dark camp. Shortly before and you'll be setting up in the dark. 2nd, when active in the field, and depending on hot times, you'll know the light conditions for sending out patrols.