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/astronomical-applications/data-services/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 (http://www.largeformatphotography.info/sunmooncalc/) 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 (http://www.ngdc.noaa.gov/geomagmodels/Declination.jsp). 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". :confused: 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. :)

[Jeff Conrad]

Ray, I don't quite follow your procedure. I think it would be much easier to get az/alt from TPE. You can set the primary marker (the large red balloon) to lat/lon by entering decimal values in the search box; unfortunately, you need to manually place the secondary marker (the small gray balloon). You can check the coordinates of the secondary marker by exchanging the markers and examining the values for the primary marker. It's best to exchange the markers to the original positions after taking this reading because if you move the primary marker too far, the secondary marker is also moved and you need to start over.

Remember that the secondary marker only picks up the ground elevation, so you can't use it for a building. You could, however, use the secondary marker to get the base elevation of the building and the distance to it, and then add the building height to the indicated elevation difference, and calculate the altitude using the formula above. It may not be quite as accurate as a geodetic calculation, but it's often probably better than you could get from a field measurement.

Elevation at the horizon: if the elevation at the secondary marker is less than the elevation at the primary marker and you click the 'Lock' button, the elevation at the horizon is set to that of the secondary marker and the distance to the horizon calculated accordingly. Bear in mind that this is simplistic because it assumes that you're at an unobstructed point above flat terrain.

[Kirk Gittings]

My assistant does the TPE thing for us every morning before a shoot. I don't know how to use it but for calculating twilight shots he is always right on the money.

[rayonline]

I meant that, prior get to the location, mark down the GPS coordinates and think where I want the sun to be, get that from the compass.

Then go home on the computer, with TPE, mark my GPS position and look at the "AZ" and play around when a sunrise for example would be in that area.

I could do it all on the computer before firstly, but I guess less precision as you don't know exactly how one is going to compose the photograph.... althou it is handy to have this on a Smartphone out in the field but I have a Nokia.


Yeah .. with the grey bubble, doesn't appear to work on my computer, it did some months back. I set my red bubble then I move the grey bubble but that textbox for altitude on the bottom of that screen is just blank .......

I may reinstall and see if that fixes it.

[rayonline]

Just 2 more queries promise!

I am in New Zealand so we are in winter. In winter the sun may rise after there is white light. Is it possible to determine when this white light occurs and to determine when darkness happens?

Re: twilight. Do I use the civil twilight times to determine when a dark blue sky would occur before sunrise and when it would conclude after sunset?



Many thanks

[Eric James]

TPE for iPhone and iPod has just been updated to version 2.0.4 and now includes a compass.

[paulr]

Predicting sunrise or sunset is an act of faith. Just because both have apparently happened every day in the past does not prove that they will happen tomorrow. Just sayin'.

[Heroique]

I just want to take a moment and thank everyone for playing.

The correct answer is just get out there and work w/ the conditions you find.

;^)

[tom thomas]

Wouldn't it be easier to get a current "Farmer's Almanac?"

[Jeff Conrad]

Ray,

It's not clear what you're asking. But a few basics.

At the endpoints of civil twilight (which I've termed dawn and dusk to denote the morning and evening phenomena), the center of the Sun is 6 deg below the horizon, and it's usually too dark for normal activities without artificial illumination. Any photography you do before dawn or after dusk is night photography. At the time of civil twilight, the sky will be close to black in most photographs that show any of the foreground.

Rise and set occur when the top of the Sun is on the horizon. The twilight arch around the rising Sun will provide some illumination before sunrise and after sunset any time of year, though the light will be quite warm just after rise and just before set. It's tough to say when "white" light will appear or disappear because it's a subjective assessment

But let's look at some examples; you weren't too specific about your location, so I've chosen Christchurch. For tomorrow, I get:

Christchurch, New Zealand
latitude -43:31, longitude -172:38, elev 112 ft
time zone -12.00 (Standard Time), mag dec 23.47 deg
Sat 7-02-2011 (Standard Time):
Day length 9:00
Dawn (Civ) 7:31
Sunrise 8:03 az = 58 angle = 138
Sun transit 12:33 alt = 23
Sunset 17:03 az = 302 angle = 138
Dusk (Civ) 17:36

At the equinox, I get:

Christchurch, New Zealand
latitude -43:31, longitude -172:38, elev 112 ft
time zone -12.00 (Standard Time), mag dec 23.48 deg
Wed 9-21-2011 (Standard Time):
Day length 12:02
Dawn (Civ) 5:54
Sunrise 6:22 az = 89 angle = 134
Sun transit 12:23 alt = 46
Sunset 18:24 az = 270 angle = 134
Dusk (Civ) 18:53

For the middle of summer I get:

Christchurch, New Zealand
latitude -43:31, longitude -172:38, elev 112 ft
time zone -12.00 (Daylight Time), mag dec 23.49 deg
Wed 12-21-2011 (Daylight Time):
Day length 15:26
Dawn (Civ) 5:08
Sunrise 5:44 az = 124 angle = 139
Sun transit 13:27 alt = 70
Sunset 21:10 az = 236 angle = 139
Dusk (Civ) 21:46

Although in the summer the day is much longer, the length of civil twilight isn't that different from that for tomorrow. There are, of course, considerable differences in the rise and set azimuths, and the maximum altitude. Note also the slight change in magnetic declination over the next six months. The "angle" is the angle of the Sun's path with the horizon at the time of rise; it's shown here as greater than 90 deg because the path is inclined toward the north.

You'll get essentially the same numbers from any decent application, though not all applications give all the information.

Noting the data for tomorrow, I'd do what several others have suggested: go out and observe the light between dawn and sunrise, and between sunset and dusk, and make your own assessment. You might also make a few photographs, noting the time of each, so you'll have a reference for the future.

[Steve Barber]

For Luddites, like me, I suggest these two sites. The first is from the US Naval Observatory, for sun and moon times anywhere in the world:

http://www.usno.navy.mil/USNO/astronomical-applications/data-services/rs-one-day-world

The second is from John Walker’s Fourmilab site and allows you to create a virtual sky for any location and time along with a virtual view of the horizon:

http://www.fourmilab.ch/yoursky/

All you need to know is the latitude and longitude of your location and the correct time in Universal Coordinated Time format, what used to be called GMT or Greenwich Mean Time, and your local time, which you can get here:

http://timeanddate.com/

[Jeff Conrad]

On the USNO site, I recommend using http://www.usno.navy.mil/USNO/astronomical-applications/data-services/mrst-us if you’re in the US, and http://www.usno.navy.mil/USNO/astronomical-applications/data-services/mrst-world if not. In addition to rise and set times, you get rise and set azimuths, transit times and altitudes, and you can get the data for several days. The one slight drawback is that you need separate queries for the Sun and the Moon, but the overall effort is still less.

[Marc B.]

With trying to keep this as simple as possible, have you tried Paul Neave's site, Flash Earth and Planetarium?

Locate your position on the globe in Flash Earth, then switch over to Planetarium.
You can then enter any time or day; past, present, or future. Alternating right clicks allows you to freeze the sky, or move around.
The site will show you the exact times that the sun or moon will rise or set in your locale, and show a simulation of sky brightness during sunsets and sunrises.

Using the time of day indicated on the site, and equipping yourself with a compass, you will have an effective and simple tool for locating the position of the sun or moon, any time of day or night.

In trying to determine the extent of shadows or reflections off buildings, nothing beats actual observation, but the Neave site will show you the exact times you'll need to be in position.

[z_photo]

Why don't you go outside and LOOK AT THE LIGHT.

The sun rises in the East, sets in the West.

That simple fact has worked for photographers from William Henry Jackson to Edward Weston to Sally Mann and many others.

damn good idea. let me run out and see what the sunrise will be like in the smokies at oconaluftee overlook on aug 23 this year. i will be back in a minute to let you know! i'll bring the ipad with TPE so I will be certain to see the August light correctly this fine July morning :D

[captivelight]

I use Google earth to tell where the sun will be at any location and any date and specific time past or future.

Download Google Earth (make sure to unclick the two boxes in the midde of the page)
http://www.google.com/earth/download/ge/agree.html

1) Open Google Earth
2) Go to the location that you're interested in
If you're wanting a sunset face West, sunrise will be East
3) Click on the Sun button (see attached image)
4) Use slider bar to adjust the date and time wanted
5) Here's the tricky part, pan around in Google Earth to see the
shot that you're looking for ( GE takes some getting used to panning,
zooming and orbiting)

It'll also show the moon rise and set.

Ben