Moon Position Help
A Glacier Gorge Example
All these angles have you bewildered? Let's work through an example.
Let's say you'll be in the park on June 27th 2007 and want to get a photograph with the moon. Sunrise
opportunities are out of the question since the moon will be below the horizon. But the Moon Position
Calculator says that at sunset, the moon will be 92% full, it's azimuth will be 147.7 degrees and it's elevation
angle will be 14.7 degrees. Now, look at your map and find a subject you would like to photograph, that
also has a place to photograph from, both on a 147.7 degree line.
For this example, a photograph of the Glacier Gorge area including Half Mountain and Longs Peak will
work. The 147.7 degree line through this area intersects with the Dream Lake trail between Nymph Lake and
Dream Lake.
This picture was taken from
the Dream Lake trail in 2006. I'm not sure of the exact spot where this was taken from, but it was between Nymph
Lake and Dream Lake. I'm guessing that a 147.7 degree line from this spot will pass between Half Mountain
and Longs Peak.
The next question is, will the moon be hidden by the mountains or will it be high enough to be seen? This
is where we need the moon's elevation angle. With your map, find the elevation of the point where you will
be taking the photograph from, the point on the Dream Lake trail. Let's say that is 9870 feet.
Now, find the elevation of an object near where the moon will be. In this case, let's choose Half Mountain,
whose elevation is 11,482 feet. Next, we need the distance between the point where the photograph will be
taken from, and our distant elevation reference, Half Mountain. You can
use your map to figure that out. Measure
the distance on the map with a ruler, and then use the map's distance scale to find the ground
distance. We need to know that distance in feet; in this case it's 9435 feet.
Next,
calculate the elevation angle to the summit of Half Mountain.
The formula for that is:
| Or: Elevation Angle = the arc tangent of ((B - A) / D) |
| | Where: | A is the elevation of the point where the photograph is taken
from, 9870 feet.
B is the elevation of the distant elevation reference, Half Mountain, 11,482 feet.
D is the distance between those two points, 9435 feet. |
The result of the equation is 9.7 degrees. That's good, since the moon's elevation angle will be 14.7 degrees,
it won't be hidden by the mountains. The diameter of the moon is equal to 1/2 degree of elevation. So
in this case, the moon will appear about 10 moon-diameters above Half Mountain.
(14.7 - 9.7) X 2 = 10
But wait, what if we're off a little and the moon is lined up with Longs Peak? Will it be hidden
then? Let's calculate that elevation angle and see. The elevation of Longs Peak is 14,255 feet and the
distance between the photographer and Longs Peak is 22,635 feet. Let's plug those numbers into our equation
and see.
Longs elevation angle = the arc tangent of ((14,255 - 9870) / 22,635) = 11 degrees. No problem, Longs Peak
won't hide the moon either. Performing this second calculation on Longs Peak gives us another piece of
information that you may not have noticed. The difference in elevation angles between Half Mountain and
Longs Peak was only 1.3 degrees, or about 2.5 moon diameters. This gives you a rough idea of how large
the moon would appear in the example photo above. If that's a little too small for your taste, you could
zoom in a little.
So there you have it. At sunset on June 27 2007, the moon should appear between Half Mountain and Longs Peak,
and about 10 moon-diameters above Half Mountain. Assuming you're standing on the right spot along
the Dream Lake trail between Nymph Lake and Dream Lake. Don't forget your flashlight.
Of course I could be totally wrong too. Even NASA once got their metric units mixed up with their english units and
crashed a probe into Mars.
Return to the
Moon Position Calculator.
