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  Be a Calculating Photographer

Great sun and moon photos requires require some knowledge of where these celestial bodies will be in the sky. Here's how you figure that out.

Updated: 6/14/2010


It helps to know where the sunrise and sunset are going to occur, especially if you want to include a particular feature in your shot. This self-portrait was taken at sunrise in Capital Reef National Park. D1x, ISO 125, Nikkor 18-35mm.

Every serious outdoor photographer I know makes it a habit to head out armed with far more information about astronomical phenomenon than just sunrise and sunset times. Computers and the Internet have supplied a wealth of tools that you need to know about and start using. With them, you can find out the exact position (including altitude and azimuth) of the sun or moon at any time of the day, the phase of the moon, the location and totality of any eclipse, and much, much more.

Two types of tools are available for calculating useful data: applications and interactive Internet sites. If all you want are some basic data points, here are two starting places, one simple, one complex:

The Seventh Day Adventist Web site is useful for foreign locations--at least those where the church has a presence--as it sports a nicely handled "select a city" feature that fills in LongLat data for you. The Photographer's Ephemeris comes as a free Adobe AIR application for your desktop or as a for-purchase iPhone application, but is far more advanced as it uses Google Maps to show you where the sun and moon rise and set in the landscape. iPhone users especially should have either Photographer's Ephemeris or Focalware. Both do a good job of helping you figure out the "where" of the sun while wandering the world.

If you need to calculate the sun's exact position at a specific time--perhaps you're looking for when the sun might be perfectly located near a prominent local feature, like a mountain peak--try the NOAA solar position calculator. This tool, coupled with some map reading skills, can help you figure out exactly where the sun will be positioned in relationship to that geographic feature you're photographing.

But the most heavenly site for photographers (pardon the pun), is one sponsored by the US Navy. Here, you'll find virtually everything sun and moon related that you might ever want to know: sunrise, sunset, twilight, moonrise, moonset, transit times, moon phase, altitude and azimuth during a complete day cycle at intervals you select, eclipses, equinox, solstice, perihelion, aphelion, Easter date, and a host of other wonderful calculators. Better still, you can obtain data for a single day, or for a month at a time. You'll need to know the LongLat and Time Zone data for international locations and others that aren't near US cities. Personally, I can't imagine any outdoor photographer venturing out on any serious shoot without first consulting the data on this site. More than once I've noticed something in the data that altered my shooting plans to incorporate the sun or moon.

Eclipses are also interesting celestial events, and many outdoor photographers like to plan them into their shoots, when possible. Did you know, for example, that there's a total solar eclipse that'll be perfect for incorporating Mt. Hood or perhaps Grand Teton National Park coming in August 2017? I didn't, at least until I discovered Fred Espenak's site. Fred works for the NASA Goddard Space Flight Center, and he keeps a page that predicts all solar eclipses out through 2030, including handy path maps and auxiliary data. Can't wait until 2017? Well, the site lists plenty of other eclipses you can chase, though you'll have to leave North America to get to most of them. (International Road Trip!)

Got a desire to "build your own?" Sky and Telescope magazine has published a wealth of program listings in BASIC over the years. The full set is available for download at One warning: these listings provide the basic calculations, but have virtually no user interface-you're on your own for making them pretty. That page also points to third party software.

Don't forget that Casio Forester watch. It's hard to find at local stores (hint: try sporting goods stores catering to fishermen), but relatively easy to locate on the Web. I've since supplemented it with an expensive Suunto watch that provides altitude and a host of other data, but probably a better choice than loading up on watches is to get yourself a GPS device.

Virtually all of the Garmin and Magellan models now include basic sun and moon information. Another choice is to get a smartphone that has a GPS unit, such as the iPhone 3GS and use applications in conjunction with the built-in GPS. Since the government has turned off the random generator that kept personal GPS units from being perfectly accurate a few years ago, you can now get excellent altitude measurements, as well (assuming you can see four or more satellites from your position).

Why do you want altitude information? Because in your location preparation you should be using a topographical map in conjunction with one of the aforementioned celestial calculators. For example, to figure out exactly where you need to be to get that perfect shot of the moon setting in the "crack" at the far western end of Yosemite valley, you need to be at a particular angle to the crack and a particular height to capture the moonset in the crack. Without the altitude information (and topo map), you'd only discover that shot by accident.

What's an Azimuth?
You probably already know the definitions for sunrise, sunset, moonrise, moonset, moon phase, and a number of other terms used by the tools described in the article in the left-hand column. But there's a few you may need some extra help understanding:

  • Altitude: In the context of celestial calculations, the distance, expressed as an angle, at which a body appears above the horizon.
  • Azimuth: The point at which a vertical line from a heavenly body intersects the horizon. Note that in astronomical measurements, the arc is measured from the South point, while in navigational measurements, it is from the North point. Make sure you know which one your tool is showing you.
  • Dawn Line: A curved line applied to a map that shows the relative position of first light at any given time. Those clocks that show a world map of where the sun is currently up have moving dawn (and dusk) lines on them.
  • Transit Time: The time at which a heavenly body crosses the meridian (mid-point in the sky) of a given location.
  • Twilight: informally, the period of time when there is light in the sky before sunrise, or after sunset; officially, there is a standard by which twilight is calculated, so you'll often see Twilight Time calculated by programs. Generally it's hard to photograph at the beginning of twilight time in the morning--you usually need a bit more light to get exposures that won't involve reciprocity calculations on your part. | Nikon | Gadgets | Writing | imho | Travel | Privacy statement | 2010 Thom Hogan. All rights reserved.