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36135Re: Sun-moon-stargazing data for JMT 2014

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  • John Ladd
    Dec 19, 2013
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      In our links area, I just uploaded my annual collection of astronomical data for the JMT.


      (US Naval Observatory times are given on these PDF files as Pacific Standard Time, so add one hour for Daylight Saving Time). 

      It includes

      2014 sunrise-sunset
      2014 moonrise-moonset
      2014 hikable hours (civil twilight)
      2014 stargazing hours (astronomical twilight)
      2014 moon phases

      This information can be useful if you are interested in any or all of the following

      1) What nights will have the best star gazing? Here you want nights where the moon rises after (or sets before) "astronomical twilight" (the time when the residual sunlight no longer interferes with the night sky).

      You will notice that new moons are associated with early moonsets (the moon has been up during the day and sets before astronomical twilight). The new moon and the days leading up to it are therefore usually your best stargazing nights and good nights to set up your camp on a high granite slab rather than in the woods.  June 21-27, July 20-26, Aug 19-25 and Sept 17-23 have the potential for the best early night stargazing. Good pre-dawn stargazing (moonset before the first sunlight appears) is about 2 weeks.before/after the peak periods of night stargazing.

      Hint: Turn off your headlamp (or use a red light headlamp) as early as possible, so that your night vision is good. Ask any companions to avoid lighting their headlamps near you.

      This year on the night when the Perseid meteor shower peaks (Aug 12), astronomical twilight will be approx. 9:41 pm but a full moon will rise at 9:12 pm and will stay up until past the next morning's sunrise. Your best time for meteors may be around 9 pm, when it is not full dark from the sun but the moon is not yet fully up. If you have a steep wall to your east, blocking the moonrise, your best time may be a bit later. As the moonrise will be a bit later each of the following nights, you might have a better meteor viewing not on the peak of the shower, but in the "shoulder" of the Perseid peak when the lighting is better for meteor viewing. Last year saw -- and next year will see -- darker night skies for the Perseid shower.

      2) How early can you start hiking and end hiking (without headlamps or a moon) if you like the faint early and late light?  Here you are looking for the "civil twilight" hours given on the Link titled "2014 Hikable hours" in the folder above. Civil twilight is the time when it become difficult to see well enough to do tasks on land.  I personally love hiking early and late whenever possible. 

      For instance, in early August, you should be able to hike above treeline without headlamps or moon from roughly 5:30 am to 8:40 pm. In July the hikable day is longer. In September it gets shorter. Obviously, in heavy treecover or on cloudy days, the hikable hours will be shorter.

      3) Do you want to do some moonlit hiking in areas above treeline? Here you are looking for lots of moon illumination and a moon that stays up either before sunrise (for early starts) or well after sunset (for late hiking). Avoid turning on a headlamp and it quickly will spoil your night vision.

      For instance, if you hope to see sunrise from the top of Whitney and will be staying at the tarns about Guitar Lake on August 11, the tables will show you that you will have a full moon that night and the moon doesn't set on the 12th until 8:34 am. Hope for a cloudfree morning and you will have plenty of moonlight to hike up Whitney. It should be gorgeous.

      The data is for Truckee, which is similar to the JMT in East-West direction, and therefore is approximately correct for the JMT.

      When I posted these last year, a member (Rob Jaworski of San Jose, California) made the following interesting observations:

      This is a great set of data, and it can be extremely useful for people out, far away from light polluted areas.

      I'm with the San Jose Astronomical Association, and one thing that we try to emphasize to people who are not accustomed to being out at night is that your eyes can get really well adapted to dark conditions, surprisingly so. It can take a while, upwards of 45 minutes for the chemistry in your eyes to adjust to the dark and be fully what we call dark adapted.  But the thing to keep in mind is that if your eyes receive any white light, that dark adaptation can get shot quickly. So if you try, keep the headlamps off.

      Full moon nights, or nearly so, are also surprisingly bright. You will have a shadow, just like you see with the sun. You can also start to make out color once dark adapted.  Again, surprisingly so.

      Regarding meteor showers, the best time to see those is usually in the wee hours of the morning. The earth is heading face-on into the debris field that makes for the shower in the early hours, so that's when you'll see the most shooting stars. It's pretty incredible, if you think about it.

      In really dark locations, like out in the middle of nowhere like many portions of the JMT, you will lose track of the familiar constellations.  There are *so many* stars that will be visible, the familiar, brighter stars that make up the constellations get drowned out by all the other starts visible in really dark skies.

      People describe the Milky Way, our home galaxy, as being 'sugary', like sweet grains of light sprinkled across black velvet.  You can see the dust lanes that block out portions of the background galactic stars.  Check it out, look up, it's truly awesome, even naked eye.  Make these observations part of your hiking log.

      In John Denver's song Rocky Mountain High, he talks about the stars themselves being bright enough to cause shadows to be cast. You won't find that from the city, but see if you can make it out being Sierra Mountains High.


      John Curran Ladd
      1616 Castro Street
      San Francisco, CA  94114-3707
      415-648-9279

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