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aguacaliente
climber
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Dec 24, 2012 - 01:56am PT
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Bruce, Half Dome looks large because the photographer used a very long telephoto lens and was far away from the barn. Another way of thinking about it is that standing back from the barn made the barn look "small," but standing back a half mile or whatever doesn't change the apparent size of Half Dome much, since it is already many miles away.
Atmospheric refraction is real, but it just bends light, which causes some over-the-horizon and vertical squishing effects (looks like horizontal stretching, a little). It does not magnify objects. The reason that the moon appears larger when near the horizon is an optical illusion, whose origin is not that well understood: http://en.wikipedia.org/wiki/Moon_illusion
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luggi
Trad climber
from the backseat of Jake& Elwood Blues car
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Dec 24, 2012 - 11:06am PT
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John I don't know if anyone has posted did read all of them...You can catch Keyes road off highway 99 just past Ceres and just before Turlock. It is posted. You will have to travel east for a while as you make your way out of the urban areas. Years ago I used to be able to catch a glimpse of what I though was Half dome out of my back door right after a good storm. I am about 60 miles away as the crow flies.
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Ed Hartouni
Trad climber
Livermore, CA
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Dec 24, 2012 - 01:48pm PT
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the combined effects of atmospheric refraction and the curvature of the Earth highlight the fact
that what we perceive may lead us to conclusions that are very different then what the
"actual" scene presents.
the angular diameters of the Moon and the Sun are roughly 0.5º, which is close to the angular
diameter of your thumb held at arms length. The appearance of a "huge moon" on the horizon
can be blotted out by your thumb... (as with the sun at sunset) demonstrating that the actual
angular diameter is not changed significantly.
Atmospheric refraction will change the position of the moon with respect to the horizon, and the
horizon that you view is not the position of the local level of the ground. For instance, if you had
a laser level at the position I was at in the central valley for the shot above, it's "dot" would be
roughly 2000' above sea level in Yosemite (though still below the local surface level). However,
our perception of the Valley, part of which is the perspective we keep in our minds from
familiarity of he place, would seem to suggest that the images produced from the valley were very
different from what we would expect.
In general we do not experience the spherical Earth phenomena, and our perception does not
incorporate it in a scene which it plays an important role... so while most people on this thread
"accept" the theoretical notion that the Earth is a sphere, they would argue passionately that the
view of Half Dome doesn't correspond to their perception of that scene, and therefore the image
is false.
Shades of the inquisition of Galileo...
In some odd way, our perceptual adaptations still dominate our thinking, even though we have
knowledge contrary to those perceptions.
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Banquo
climber
Amerricka
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Dec 24, 2012 - 01:56pm PT
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On Thursday it should be light until 5:21 and the moon rises at 3:48. Looks like a good day if the sky is clear and no fog.
U.S. Naval Observatory
Astronomical Applications Department
Sun and Moon Data for One Day
The following information is provided for Merced, Merced County, California (longitude W120.5, latitude N37.3):
Thursday
27 December 2012 Pacific Standard Time
SUN
Begin civil twilight 6:46 a.m.
Sunrise 7:15 a.m.
Sun transit 12:03 p.m.
Sunset 4:52 p.m.
End civil twilight 5:21 p.m.
MOON
Moonrise 3:48 p.m. on preceding day
Moonset 6:31 a.m.
Moonrise 4:39 p.m.
Moon transit 11:58 p.m.
Moonset 7:15 a.m. on following day
Phase of the Moon on 27 December: waxing gibbous with 100% of the Moon's visible disk illuminated.
Full Moon on 28 December 2012 at 2:21 a.m. Pacific Standard Time.
MERCED, CALIFORNIA
o , o ,
W120 29, N37 18
Altitude and Azimuth of the Moon
Dec 27, 2012
Pacific Standard Time
Time, Altitude, Azimuth
15:45, -9.8, 55.8
16:00, -7.3, 58.3
16:15, -4.9, 60.6
16:30, -2.3, 62.9
16:45, 0.7, 65.1
17:00, 3.1, 67.2
17:15, 5.7, 69.3
17:30, 8.4, 71.4
17:45, 11.1, 73.5
18:00, 13.9, 75.5
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Ed Hartouni
Trad climber
Livermore, CA
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Dec 24, 2012 - 02:56pm PT
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check your times... easy to have different definitions depending on how many hours from Greenwich (right now -8)
your table is similar to mine posted above, moon rise is at 4:50pm or so
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Ed Hartouni
Trad climber
Livermore, CA
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Dec 24, 2012 - 06:23pm PT
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seems like Thursday will be clear from noon on...
Wed is chance of showers and cloudy all day long...
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BillO
Trad climber
Yachats, OR
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Dec 24, 2012 - 08:07pm PT
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Gonna have to see if I can find that valley shot on one of my drives up the 99.
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Ed Hartouni
Trad climber
Livermore, CA
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Dec 25, 2012 - 05:27pm PT
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wed looks dreary, sorta like today...
thu looks less definite, with some cloud cover forecast... but the weather model shows hopeful signs as well as the forecasts
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Ed Hartouni
Trad climber
Livermore, CA
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Dec 27, 2012 - 12:35pm PT
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I'll be there this afternoon/evening to shoot whatever happens...
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john hansen
climber
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Topic Author's Reply - Dec 27, 2012 - 01:27pm PT
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Hope you get the shot Ed,, good lick
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Ed Hartouni
Trad climber
Livermore, CA
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Dec 28, 2012 - 03:44am PT
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thought that the atmosphere would be the problem tonight, it was the low clouds hanging on the Sierra, and obscuring the Sun set...
...got to see the Moon rise over the crest, though, but no Half Dome view...
I'm still analyzing the images to get an idea of my calculations for the next time, here are the 71 images I shot at 30 second increments. It's still a great thing to see the Moon rise on the horizon when and where you expect it too... set the camera up, and let it shot automatically.
[Click to View YouTube Video]
shot with my Fujifilm S5-Pro and Nikon 180mm lens
ISO 100, 1/125 s exposures
varying apertures f11, 8, 5.6, and 4 corrected with Photoshop
timed with Nikon MC-36 15s increments alternating between "mirror up" and "expose"
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Patrick Sawyer
climber
Originally California now Ireland
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Dec 28, 2012 - 08:00am PT
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Back in 1975, sitting in Don Reid's van in C4, he showed me a photo of Half Dome (and a bit of the Valley), taken from the top of Mt Diablo. Now the crap sandstone on Mt Diablo is where I cut my teeth climbing, and I was up there a lot from 1970-74.
I wasn't sure if the photo was real. Several years later, back up on my old stomping grounds and I went to the summit with a friend's telescope. Sure enough, there it was. It was a very clear day with no haze, fog or smog. And the top of El Cap was also visible.
They say you can also see Mt Shasta from the top of Diablo. I never have.
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mouse from merced
Trad climber
The finger of fate, my friends, is fickle.
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Dec 28, 2012 - 09:38am PT
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"Hey, way out there," Patrick! (the best I could do for a view of what you wished to see)
Search "Mount Diablo Vistas" on "Google" "OK"?
"Mouse"
I posted the copied link, but it's failing.
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mouse from merced
Trad climber
The finger of fate, my friends, is fickle.
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Dec 28, 2012 - 11:11am PT
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This morning, just After Seven, from Mouse's.
No wind last night, freezing at rooftop level.
That moonrise was real nicely-edited and the music's mellow, Ed. Good on you.
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Banquo
climber
Amerricka
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Dec 28, 2012 - 01:03pm PT
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I went to take a look but from a different spot than Ed. I opted for a shorter drive from my house. This was taken from the I5 overpass at Taglio Road near Gustine.
Based on the Naval Observatory http://aa.usno.navy.mil/data/docs/AltAz.php the predicted Gustine moon position was:
PST ------ Alt(deg) - bearing(deg)
16:46 ----- 0.5 ------ 64.9
16:47 ----- 0.7 ------ 65.1
16:48 ----- 0.8 ------ 65.2
16:49 ----- 1.0 ------ 65.3
16:50 ----- 1.1 ------ 65.5
From my location Half Dome should have been in a bearing of 66.3 degrees and 92.5 miles away. I've sketched in Half Dome roughly the correct size but I simply guessed how high to place it in the image. The clock in my camera was about 12 seconds slow if you check the EXIF data.
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Banquo
climber
Amerricka
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Dec 28, 2012 - 01:58pm PT
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DMT -
Yeah, moon photography is a problem. The moon is in full sunlight and should be exposed accordingly. Dusk is getting pretty dark for the terrestrial part of the image. Summer would be good since the sun sets much later but the visibility is never good then.
The next full moon is on Jan 27 but it doesn't rise until 6:30 pm when it will be too dark to see half dome.
On January 24 the moon will be 95% and rises at 3:30. This might be good enough if it is clear.
Dan
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Ed Hartouni
Trad climber
Livermore, CA
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Dec 28, 2012 - 02:01pm PT
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the trick will be to get the Moon rise with sun still on Half Dome
and with a very long lens... which stresses the accuracy of the calculation of the trajectory of the Moon as seen from some location in the central valley...
I'd hope to get 360mm or 500mm lens on the scene, perhaps even 1000mm if the light is excellent...
the angular field-of-view at 1000mm is about 1.4º on my sensor, the Moon is 0.5º so it takes up a very large area, but it's also moving fast, requiring a quick exposure time... the aperture can be set larger than the typical full Moon setting of f11 at 1/125 s because the atmospheric attenuation is large viewing it on the horizon... looks like f4 at 1/125 s was fine for my last effort... 3 stops down (1/8 th the light) but that doesn't give much room for the exposure unless the lens is very fast (my 500 mm reflex is f8, with a x2 teleconverter this goes to f11)... if the scene is too light, the Moon-sky contrast is not so great and the effect is diminished...
anyway... it's a fun project...
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Banquo
climber
Amerricka
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Dec 28, 2012 - 05:54pm PT
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Ed-
If Jan. 24 is a clear day it should work.
Good, long focal length lenses are terrifically expensive. I see some nice ones in the 10 k$ range but I won't be buying one. I have a super cheap 500mm reflex lens but it is hard to get good photos with. My aging eyes have trouble with the manual focus and like all reflex lenses the contrast is poor. If one had a big mega pixel camera and a good lens in the 200mm range, a cropped image might do.
I did learn a few things yesterday that will be helpful if I try again. The position predicted by the Naval Observatory seems to match the photo I got. It seems like they must account for atmospheric effects. I would try to get an image when they predict the moon is about 0.7 degrees elevation. I think it would look best with the moon a bit left of HD so I should have been a bit farther south than I was.
My next target is about 3:27 pm on January 24. The moon will be on a bearing of 64.5 degrees. I think a position along a bearing of 65 degrees from HD would be just about right. By I5 where Butts Road crosses the California Aqueduct would work and There is some elevation there to look over the orchards. Also Lincoln Blvd about 0.5 mile south of 140 if there is a clear view from there.
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Ed Hartouni
Trad climber
Livermore, CA
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Dec 28, 2012 - 06:25pm PT
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right now my climbing schedule will have me in Cody WY on the 24th... so I'll miss that one... try for Feb.
I suspect that the differences between the "apparent" altitude and the "actual" would be more to do with timing than with position as the corrections are pretty small...
most of the lenses I've bought are used, that brings the price down a bit... and getting a teleconverter 1.4x and 2x helps though they can soften the focus a bit and reduce the light by a half stop to a full stop, with fast primes I haven't found this to be a limitation.
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