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    Twilight Star Card
    From: Greg Rudzinski
    Date: 2014 Sep 20, 10:26 -0700

    Twilight periods (Civil, Nautical, Astronomical) offer only a limited period of time to observe stars and planets for most latitudes. It is therefore important to plan observations prior to actually taking them during optimal twilight when both a sharp horizon and a body are clearly visible.  Pre-calculated altitudes and azimuths arranged on an index card will help with sextant pre-setting and orientation from the cockpit. Pub 249 vol. 1 is handy for working up star selections for the twilight star card. Enter 249 vol. 1 with assumed latitude and LHA of Aries for civil twilight and record up to 7 pre-calculated stars. Polaris can also be pre-calculated using a dedicated table in the back of 249 that is entered with the LHA of Aries for civil twilight. Now a round can begin with a pre-set scoped sextant,  stopwatch,  recording tools, and a flash light. No reductions are to be done until all the planned observations are recorded. The attached index card shows six stars for evening civil twilight at my current location. An arrow is placed at North up. At sea it is helpful to have the card arranged with an arrow showing the Bow up. Observation order is also important. Start away from the setting sun and toward the rising sun.

    Greg Rudzinski



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