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Sun and moon data added to files area

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  • John Ladd
    As you have already seen from Yahoo s notification process, I uploaded a moonrise/moonset table to the group s files area -- in furtherance of our discussion
    Message 1 of 1 , Jan 6, 2010
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      As you have already seen from Yahoo's notification process, I uploaded a moonrise/moonset table to the group's files area -- in furtherance of our discussion of stargazing at above-treeline campsites. 

      I also uploaded sunrise/sunset and twilight tables.  I working on uploading a moon phase table.

      The data is for Truckee, CA.  For all practical purposes (except maybe resetting your watch), that should be close enough for the entire JMT since N-S differences don't much affect these times (mostly they depend on east-west distinctions).

      The Sunrise/sunset table is pretty obvious.  But the twilight table (see below) may be more useful.

      Moonrise/moonset will let you know nights where you can either

      stargaze because moonrise is enough after sunset

      walk into the night (at least above treeline) with moon illumination - moonrise before sunset

      start in the early morning - moonset after sunrise - lots of people do this on their ascent of Whitney at the end of a SoBo trip

      but compare the moon phase table if you are counting on night hiking.  A new moon, even if it has risen, won't give you much light.  And think about where you plan to hike.  Above treeline, and if it is not cloudy, you can usually hike in anything over a quarter moon without need of a headlamp.  Tree cover, new moons, or clouds will force you to use the headlamp.

      One explanation - the "Civil Twilight" table may actually be more useful than the sunrise/sunset table.  It sets the limits of when you have enough light to walk without a headlamp.

      From the Naval Observatory website (where you can generate these tables)

      Civil twilight is defined to begin in the morning, and to end in the evening when the center of the Sun is geometrically 6 degrees below the horizon. This is the limit at which twilight illumination is sufficient, under good weather conditions, for terrestrial objects to be clearly distinguished; at the beginning of morning civil twilight, or end of evening civil twilight, the horizon is clearly defined and the brightest stars are visible under good atmospheric conditions in the absence of moonlight or other illumination. In the morning before the beginning of civil twilight and in the evening after the end of civil twilight, artificial illumination is normally required to carry on ordinary outdoor activities. Complete darkness, however, ends sometime prior to the beginning of morning civil twilight and begins sometime after the end of evening civil twilight.

      Source of the tables - US Naval Observatory site:


      That page also allows download of data that can be imported into a spreadsheet if you want to arrange the data in a more convenient form.

      John Curran Ladd
      1616 Castro Street
      San Francisco, CA  94114-3707

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