How to determine sunset & sunrise times and locations
by Chris Nicholson

That's true. As long as you're not planning to travel far in the next day, then determining sunset and sunrise times is as simple as this:

1. Today, wait for the desired solar event.
2. When it happens, note the time and the compass point of the sun's location on the horizon.
3. Tomorrow, both will be the same.

But traveling can thwart that strategy. Moving from one side of a time zone to the other can change the time of sunset by over an hour, and moving from north to south just a few hundred miles can affect that time by 15 minutes. As for location, traveling 700 miles north or south will change the sun's spot on the horizon by about 3°.

Therefore, having access to some tools can help photographers precisely determine specifics about sunrise and sunset.

GPS

The cost of GPS receivers has dropped dramatically in the past couple years, while the features have steadily improved. Many receivers on the market will report sunset and sunrise times for the spot you're standing in, and the Magellan Meridian receivers offer the sun's compass points as well.

The Garmin eTrex Summit is one GPS receiver that reports sunrise and sunset times for any location on Earth.

On the web

If you have web access on the road, or if you want to prepare your research from home before you leave on a shoot, you can find sunrise and sunset data in many places on the Internet.

The Astronomical Applications Department of the U.S. Naval Observatory computes the sunrise and sunset times for either a specific day or an entire year (presented as a chart) for any location in the world. Another utility on the site will figure the position of the sun at any time of day, which you can cross-reference with the sunset or sunrise time.

If you'd like to avoid cross-referencing two utilities, try Location Works. There, a reckoner will tell you when and where the sun will rise and set for most world locations, though the user interface is more awkward than the Naval Observatory's.

Also, the website 40-below.com doesn't give the sun's location, but it does give sunrise and sunset times via a convenient clickable map of the United States. At SunriseSunset.com, you can generate a calendar with the times.

The Herzberg Institute of Astrophysics has a sunrise/sunset utility that has an interesting added feature: In addition to giving the times and locations, the site can tell you the angle of sunlight for any time of day. The utility can be slightly complex to use, as not all world locations are listed (it's mainly a Canadian service); but you can enter the latitude and longitude of any location to get the sunrise/sunset information.

Via software

If you'd like to determine sunrise and sunset date from your desktop or laptop computer, download Ephemeris 2.0 freeware from Digital Light & Color.

Another more convenient way of calculating the sunset or sunrise time in the field is by using a PDA. Several software programs meet the task handily: two are Sol! (also available in a Windows version) and Planetarium. Ephemeris 1.0 and Sun-Compass (both freeware) are similar PDA applications that also provide the sun's location.

Explanation

If you're really into math or astronomy (I mean really into it) and you're interested in how all this data is determined, the U.S. Naval Observatory explains the algorithm. Good luck.

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