Twilight Over the BigHorn Mountains is of course a night sky in late civil twilight. The 13000 foot high peaks at 130 miles out from my lens. This is a 2 second time exposure and it was very dark out. Once the sun goes down, there is still an hour and a half sky show through the three twilights. You just need a good tripod and time exposures to see the show sometimes. I have photographed many of these from start to finish. This week has been incredible.
Civil Twilight begins about 28 minutes before sunrise or ends 28 minutes after sunset. It is that period from when the sun is about 6 degrees below the horizon. On clear days you can do normal outside activities that require light. That solar elevation angle below the horizon defines each twilight phase. CIvil Twilight is by far the brightest of the three twilights.
Nautical Twilight starts when the sun is 12 degrees below the horizon technically. Both the Horizon AND brighter stars/planets are visible in this twilight. It is the “middle” of the three twilights. At the beginning of Nautical twilight, it’s about one hour to sunrise. Rule of thumb which varies with your position on the globe, is 28 minutes each twilight.
In Astronomical Twilight, If you live in the city, you have probably never noticed astronomic twilight. The are NO shimmers of daylight at the beginning of Astronomic Twilight a full hour and a half before sunrise. . Away from the lights of population centers, we see Astronomic Twilight regularly where there is just a slight greying of the black totally dark sky mid night. It gets as dark here on our ranch in remote northeastern Wyoming as the North Atlantic Ocean according to NASA.
Location: Bliss Dinosaur Ranch, Wyoming/Montana borderlands
Title: Twilight Over the BigHorn Mountains