Tuesday, September 28, 2010
X Marks The Spot
New tools to guide you to the perfect place for the perfect photograph
Let’s say you want to know the best day in 2011 to shoot the full-moon setting over Longs Peak, at the moment of sunrise, from the summit of Twin Sisters. Start by opening The Photographer’s Ephemeris and searching for Longs Peak, Colorado (Twin Sisters isn’t in the database). Drag the Primary Marker northeast across the map and drop it on the summit of Twin Sisters. Right now, the date doesn’t matter. Switch to Details view, and drop the Secondary Marker on the summit of Longs Peak. Jot down the azimuth shown in the info panel— the compass bearing from Twin Sisters to Longs Peak. I got 246 degrees. You’ll want the moon, at sunrise, to have a similar bearing. Twin Sisters is about 2,800 feet lower than Longs Peak, so you have to look up slightly to see Longs’ summit. That angle, the altitude, is also shown in the info panel. I get 4.7 degrees. The moon must be higher than that angle for you to see it; any lower, and it would be hidden behind Longs Peak.
The moon doesn’t have to be precisely over the summit of Longs to get a good photo; there’s actually a range of acceptable angles. Drag the Secondary Marker a bit left of Longs and note the azimuth. Drag it a bit right and do the same. Let’s say the acceptable range of moon positions is from 235 to 256 degrees.
Now open Heavenly-Opportunity. On the home page, press the Search For button. A dialog opens that lets you enter the desired range of moonset positions—235 to 256 degrees—and the desired time of moonset, expressed in terms of minutes before or after sunrise. In this case, we want the moon still to be above the horizon at the moment of sunrise, so the acceptable range of moonset times is from 0 minutes before sunrise until, let’s say, 60 minutes after. Sixty minutes is merely a rough guess to narrow the range of dates the program returns.
Press Display Results, and Heavenly-Opportunity provides a list of dates when the moon will set between 235 and 256 degrees, sometime between the moment of sunrise and one hour later.
So far, so good—but there’s another wrinkle to consider. We actually don’t want to know the bearing to the moon when it sets. We want to know where it will be at the moment of sunrise, which in this example could be as much as 60 minutes earlier. Let’s go back to The Photographer’s Ephemeris.
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