How to use the twilight phase duration calculator
Copy the sunset time and the civil, nautical and astronomical twilight ends from an almanac for your location, and the page reports how many minutes each phase runs, how long the whole twilight span lasts and which phase is the longest. When the speed of darkening matters, as it does for setting up a telescope or planning outdoor work after dusk, reading the phases separately makes the margin obvious. For high-latitude tables whose twilight ends pass midnight, switch the midnight option to yes.
How the numbers are produced
The phase boundaries use the standard sun-altitude definitions. Civil twilight runs from 0 to minus 6 degrees, nautical from minus 6 to minus 12 degrees and astronomical from minus 12 to minus 18 degrees, and those angles are printed in the sun altitude column of the result table. The lengths themselves are differences between the times you entered, measured in minutes, as of October 2026.
Limits and what is not covered
Golden hour and blue hour for photography are not covered. Sunrise, sunset and twilight moments differ by site, so the page does not compute them and takes them as input. It also ignores atmospheric refraction corrections, the real brightness produced by moonlight and weather, and any correction for the elevation of the observing site.
Frequently asked questions
By the altitude of the center of the sun. From 0 to 6 degrees below the horizon is civil twilight, 6 to 12 degrees is nautical twilight and 12 to 18 degrees is astronomical twilight; below 18 degrees it is astronomical night.
Those moments depend on the latitude, longitude and elevation of the observing site, so no single value fits everywhere. The page therefore estimates no times and only measures the lengths between the values from the table you are reading.
Yes. Enter astronomical twilight begin, nautical twilight begin, civil twilight begin and sunrise into the four fields in that order, earliest first, and the phase lengths come out the same way.