| Sun Cycle Calculator
NOTE: The program expects latitude and longitude in fractional degrees, not degrees and minutes. Thus 27° 30’ north should be entered as ’27.5’ (i.e., halfway between 27° N and 28° N).
Sun time estimates are approximate for several reasons:
NOTE: The U.S. Naval Observatory hosts a web page (USNO Sun and Moon Data) that permits very accurate calculations of solar and lunar data. It incorporates ‘fixes’ for many of the issues described above, and — if you are connected to the internet — can be accessed with the ‘Naval Observatory Website’ button.
• The 'Get Latitude and Longitude From World Map' button opens a window with a world map (d'oh!) in Mercator projection. Move the cursor to the desired location and click the mouse to select that position; as you move the cursor the latitude and longitude boxes at upper left update continuously. If you want to select a position on a higher-resolution 'regional' map, click the Zoom in X5 button, a rectangular cursor appears; move it until it encloses your area of interest and click the mouse to enlarge that region. Then select a position on the enlarged map as described above.
Location data are accurate only to 0.33 degree of longitude and 0.25 degree of latitude on the world map and 0.067 degrees of longitude and latitude on the regional maps, but that should be accurate enough for most sunrise-sunset calculations.
As geographic references, the maps show the equator (yellow), the Prime or Greenwich Meridian (zero degrees of longitude), the Arctic and Antarctic Circles (~ 66.5 degrees N and S), and the Tropics of Cancer and Capricorn (~ 23.3 degrees N and S). Only a few of these will be visible on the enlarged regional maps.
Of course, if you want higher-resolution position data (and you are connected to the Internet), use Google Earth.
• The 'Annual Plot' button will compute and display an entire year's day length cycle, based on latitude-longitude position. The 'Print Data to Spreadsheet' button makes a tab-delineated .xls spreadsheet containing the annual cycle (date, sunrise time, sunset time, and day length). This example shows a Polar-region cycle, with complete darkness in winter and 24-hour sunlight in summer: