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Thread: Astronomical twilight question

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    Default Astronomical twilight question



    How long after sunset does astronomical twilight start?

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    Default Re: Astronomical twilight question

    Civil twilight begins at sunset and lasts until the geometric center of the Sun is 6° below the horizon.

    Nautical twilight begins when civil ends and lasts until the geometric center of the Sun is 12° below the horizon.

    Astronomical twilight begins next and lasts until geometric center of the Sun is 18° below the horizon.

    The duration of twilight and its subsets depends on one's latitude and time of year.

    Great article here that explains everything quite well: https://en.wikipedia.org/wiki/Twilight
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    Default Re: Astronomical twilight question

    You can generate a full year table of sun/moon rise/set and twilight times on numerous websites. Other websites let you do the calculation for a single day and apps display it for a particular date set in the app or the time and date on the device clock.

    At the beginning of each year, I generate tables of sun/moon rise/set and twilight times using the USNO one year calculator and put together an almanac for my observing region. My standard almanac includes a list of dates for phases of the Moon, sun/moon rise/set and astronomical twilight times. I then have a list of meteor shower dates and anything else that I know is coming up like solar and lunar eclipses. Takes me a few hours at the start of the year, saves me a lot of time planning observing during the year.

    This is the link to the sun/moon rise/set and twilight times calculator
    https://aa.usno.navy.mil/data/docs/RS_OneYear.php


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