Predicting sunrise/sunset

[rayonline]

Hi, I have downloaded the software TPE and visited various sites now just reading on the terms eg, civil and nautical.

My question. I am wanting the sun behing the subject. How do I pinpoint a subject (like a building or sculpture). Is the only way of using TPE software and look at the map or get its GPS coordinates and refer to a website calculator (TPE does not allow one to add in a GPS coordinate, looking at the map guestimating can be tricky as well).

Thanks.

[al olson]

The Naval Observatory site, http://www.usno.navy.mil/USNO/astron...ices/alt-az-us, will give you a table of sun and moon positions for your location. The table contains the altitude and azimuth for every ten minutes for the date of interest.

Then find a topographic map to locate your subject. Knowing when (date and time) you want to photograph, use the azimuth from the table to draw a line from the subject, away from the sun. This line will be the best location to place your camera.

[msk2193]

TPE will show you exactly from where and at what andle the sun will be shining at any given time and date. If you use the iPhone or iPad version, you can easily switch betwen maps and streetview with the 3-D like images of each structure. The azimuth and altitude of the sun are stated and with the simple Clinometer or Carpenter apps you can tilt the phone to those anglers and voila!
Some of uf use the TPE app frequently for outdoor shooting.

p.s. I find VelaClock an easier app to use than TPE!

[Larry Gebhardt]

Do you have an iPhone? There is a Sunrise, Sunset app that will show the position of the sun for a location based on time of day and date. Combined with a better compass than the one in the iPhone you can figure out where the sun will be relative to your current position. That should let you move around to get just the effect you are looking for. I'm sure there are apps for the Android phones as well, but I haven't used them. Look for one the can give Inclination and Azimuth based on GPS coordinates and time.

[Scott Knowles]

The TPE app allows you a location where you're at or want to be and a distant location or subject (under details). Yes you need the location both yourself and the subject, but there are enough apps to do that. Then you can see the sun/moon rise and set along the line between the two locations to time your visit. I use it to determine when the moon will rise near Mt. Rainier from my home, adjusting for local terrain (something TPE or any of the calculators can accommodate). All I needed was the location of my home and a compass direction for Mt. Rainier determined from a line between the two points on a map app.

You can turn it around by making the subject that location and then see where you need to be when the sun or moon rise or set is in the right position to your subject. But again it won't accommodate local terrain or interference from cities (buildings, towers, etc.) or nature (trees, etc.).

[jp]

On my android phone, I have installed "ShadowFacts" which tells the azimuth and elevation for any given time at a location. You can enter location or use the GPS. It also has an inclinometer so you can visually see the elevation you are dealing with.

[rayonline]

No, I have Nokia. And no iPad.

Is Amizuth the angle where the sun or moon will be? So TPE shows me this. So, can I use a compass outside to get the Amizuth and match it up?

I'm not sure if my Garmin 60Csx has Amizuth but I will check.

[Jehu]

Magnetic North can be a tricky thing. If you use the magnetic declination shown on a local USGS quad map then you can apply that and be pretty close. That will get you to grid North which is normally pretty close to true north. Quads are normally drawn on a Transverse Mercator. The map angle (true north - grid north) can vary greatly.

Leave it to a land surveyor to complicate things. We're good at that.

[Jeff Conrad]

TPE will give you the azimuth and altitude from a camera position to a natural feature (such as a mountain) using the secondary marker (the gray one) in Details view. Place the main marker at your camera position and the secondary marker at the feature; TPE will show the apparent altitude, change in elevation, distance, and bearing (azimuth).

The elevation data (and consequently the altitude) may not be accurate enough if you want a close alignment (the diameters of the Sun and Moon are both about 0.5 deg), especially if you need the elevation at the base of a man-made feature (more on this below). You can usually get more accurate data from Google Earth or an application such as National Geographic TOPO! or Delorme Topo North America; a nice feature of TOPO! is that you can export lat, lon, and elevation to the clipboard for use in another application. Sometimes no electronic source is completely reliable: most of my applications tell me that the elevation of Yosemite's Glacier Point view point is about 6500 ft, which would put it halfway down the cliff.

For short-to-moderate distances, treating the Earth as flat will often suffice. The calculation is simple: take the inverse tangent of the elevation difference divided by the distance (you need to use the same units for both). For example, if the distance is 4 miles and the elevation difference is 3000 ft, the altitude is approximately

arctan[3000 / (4 x 5280)] = 8.1 deg.

If you want the best accuracy, you need to do a geodetic inverse calculation like that done by TPE. The US NOAA's National Geodetic Survey provide an online calculator; using it is described in the Tutorial for the Sun/Moon Calculator on this site. The process is admittedly a bit tedious if you have many points.

For man-made landmarks, you need to add the height of the building to the ground elevation before performing either calculation. The heights of many well-known buildings can be found from online sources, but it's yet another task.

You can measure azimuth and altitude in the field using a compass and clinometer, but you'll be doing well to measure azimuth to better than about a degree, and altitude to better than about half a degree, which, as noted, is a pretty large error. If you're a surveyor, you can get more accurate measurements with a theodolite, but this is clearly not an option for most people. Even with a theodolite, you need to take astronomical readings if azimuth is critical.

You should note that a compass indicates magnetic north, so you need to compensate for the magnetic declination to get true north. Be aware that declinations change over time, so that the value from an old topo map may no longer be accurate. The Sun/Moon Calculator will calculate current magnetic declination; the NOAA provide an online calculator. The Sun/Moon Calculator can give Sun and Moon azimuths relative to magnetic north, but I don't usually recommend the latter, especially when searching dates for an alignment.

If this all sounds like a bit of work, well, it is. But the amount of work you need to do depends on how fussy you are about positioning the Sun or Moon near a feature; obviously, the closer you want things, the more careful you need to be. Of course, you might just be driving south in New Mexico and notice the Moon rising above a cemetery. But you've got to ask yourself one question ...

[rayonline]

Thank you for that

I think I may go for a bit simpler method.
I have now with me a Garmin GPS device. I have changed the format so the readout is the same as TPE. They seem to be v accurate (where I am right now).

What I might do is think where my camera will be, mark my position or write it down. Get my compass out and think of the range where I want the sun to be. Write that down also. On the computer, TPE, mark my position via trial and error until the coordinates are close enough (on the map). Look at TPE's, Amizuth - and compare it to my compass's bearings? My GPS compass has true compass bearings. As well as magnetic.

If it is a tall building, yes I can find out the height of it and use the grey bubble on TPE, I have gone thru with the video tuturials

But re: TPE, that grey bubble does not appear to give you the altitude anymore? Under TPE Detailed right at the bottom "Elevation at the horizon". I however still have the degrees that I can compare, ie., the subject (like a bridge or building) to any high mountains that may be blocking it.

Ps. With tall buildings etc. I may need to spend more time to calculate the amizuth from that, as that's not on TPE (or I don't think it is). Please comment on the above method.