Sun/Moon Calculator Altitude ?

[peter korzaan]

In tutorial
"Advanced Calculations: Rise/Set Criteria
Getting the Times of Rise and Set When the Horizon Is Not Level"

Standard times of Sun and Moon rise and set assume a level horizon ... Suppose, for example, that the hills to the east have an altitude of 3° and the mountains to the west have an altitude of 8°. "

Ok.. how does one measure this?
Is there an inexpensive instrument?

I'm located in Sedona Az, and discovered this calculator last year. It has been very useful, but when down in the bottom of the Oak Creek, with high Cathedral Rock above, I missed the correct location this past summer because the fly by seat 'guess' was off on where the moon would rise in relationship for the picture.
I understand that elevation here 3500-4000+ feet is part of the computation, but how does one measure the altitude of the ridges to put into the calculation.
Thanks p.

[z_photo]

if you make the simple assumption that the sun correction can be calculated based upon the sidereal rate... 360 degrees per 24 hours (or 15 degrees per hour or .25 degrees per minute, or perhaps easiest of all 4 minutes per degree) and you get a pretty good guess. that gives you a 12 minute shift for the 3 degree hills and a 32 minute shift for the 8 degree mountains

[peter korzaan]

Ah... excellent, that gives me time, but how does one actually 'find' measure the angle?

[Ralph Barker]

Ah... excellent, that gives me time, but how does one actually 'find' measure the angle?

One can find inexpensive "angle finders" at the local hardware store. Just sight along the top of the angle finder to the top of the mountain, and then note the angle on the dial. Or, a protractor could be used for the same purpose.

[Jeff Conrad]

The best way to measure altitude is with a clinometer; some compasses even have one built in. I use a Suunto PM5, with which I can usually get the angle within about 1/2 degree (i.e., the Moon's diameter), but at about $130, it's a bit pricey. An angle finder, as Ralph suggested, might also do the job, but I haven't actually tried one.

Most of the time I calculate altitude and azimuth rather than measure them, because I usually can get much better accuracy, and because once set up, it's a lot faster and can be done at home. To do the calculation, you need the lat, lon, and elevation of the camera position and the landmark. It's then possible to get the distance, azimuth, and altitude. The NOAA's National Geodetic Survey have an online calculator (which is linked in the tutorial) that will do the calculations, though the output isn't the most photographer friendly (it gives zenith angle rather than altitude). The NOAA calculator is fine if you only have only a few locations, but it gets tedious if you have many; they also offer a downloadable version that includes the source. I use a program based on the NOAA's code to do my calculations, and simply read the coordinates from a database of locations and landmarks. It's very fast and easy, but does take some work to set up, especially building the database.

I get the location coordinates from a digital topo map. I use National Geographic's Topo!, which unlike most others, includes elevation in the exported data. With most others, it's still possible (though tedious) to manually read and transcribe the elevation from the on-screen display. It's also possible to get lat, lon, and elevation from the USGS GNIS (linked on the calculator's main form), but caution is sometimes needed because a feature isn't always located where you might expect (e.g., Yosemite's Glacier Point is on the side of the cliff rather than at the observation point).

Though calculations are fast and accurate, they obviously don't account for little details such as trees (or buildings in an urban location), so some field work to confirm that the landmark is actually visible from your planned camera location is usually indicated. A clinometer can be handy for a sanity check to ensure that the calculation wasn't based on garbage data (speaking from experience ...).

A location's elevation is taken into account when computing the Sun's or Moon's altitude; at higher elevations, the atmosphere is less dense, so there's a bit less refraction. But unless the body is within a degree or two of the horizon (e.g., 0 degrees), the effect of elevation is usually minor.