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Modern technology of Global Positioning System and the GPS units are all about to find precise location and navigate accurately and comfortably. But before using GPS, people used other methods and are still using them for navigating. By measuring Sun’s location and keeping time, one can determine longitude of location, or vise versa bu knowing location and position one can estimate time of day, this concept is used in sundials. Latitude of any place in northern hemisphere is the elevation of North star from horizon in degrees. 

This MS Excel workbook is about finding Sun’s position in the sky. If you have a GPS receiver then you know the geographic coordinates of location within accuracy of three meters and you can find position of sun for particular date and time. 

By using functions Sun_Zenith_Azimuth and Sun_rise_noon_set you can design a sundial for any location and you do not need to calculate equation of time, and differences of apparent local time and local standard time.

For more info on Sundials try

The North American Sundial Society 

 Sundials on the Internet.

The main Algorithms and functions are from NOVAS and Astronomical Algorithms book By Jean Meeus published by Willmann-Bell, Inc.If you click on f_x and then scroll down at Function Category: at User’ Defined section you will find these functions:  

 Day_Number(Y,M,D)           

                  Y= Year, in YYYY format, like 2007 

                  M= Month Number, such as 3 for March 

                 D= Day number in the corresponding month

  It returns Number days passed since beginning of year. 

DayNumber to Date(Year, DayNumber,N)     

       It is reverse function of Day_Number it returns date.

            Year=Year

            DayNumber= Number of days passed beginning of year.

            N= An integer,

          N=1 function returns month          N=2 function returns day number in month

 DecimalDegree(Decimal, Minute, Seconds)  

      Usually geographic coordinates indicated in Degrees, minutes and seconds. This function converts to decimal degrees       used by other functions.For example –79 25’ will change to –79.41666

  IsLeapYear(Year)   

         This is a logical function, which returns TRUE if Year is a leap year. 

  Sun_rise_noon_set(year, month, day, lon, lat, Height, TZ, N) 

       Lon= Longitude in degrees. Longitudes in west of Greenwich are negative. 

       Lat= Latitude in degrees. Latitudes south of equator are negative.

       Z= Time Zone, Time difference of an area and Greenwich time, considered negative at west of Greenwich.

       Height: Elevation above mean sea level

       Returns Sunrise if N=1              Noon if N=2              Sunset if N=3 

 Sun_Zenith_Azimuth(Year, Month, Day, Hour, TimeZone ,Lon , lat, Height , N) 

           Returns:   

           N1, Zenith Angle in degree, Astronomical elevation is 90- Zenith.

           N= 2, Azimuth angle, East ward from North for northern hemisphere and west ward from South

           N= 3, Topocentric (Center of Earth) Right Ascension of sun in hour, referred to true equator and equinox of  date, affected by atmospheric refraction.

           N=4, Topocentric declination of sun in degrees, referred to true equator and equinox of date affected by atmospheric refraction.

           N=5, Distance of earth to sun in Astronomical Units, AU

Incidentangle(year, month, day, hour, TimeZone, Log, lat, Height, Tiltangle, SurfaceAzim) 

                 Tiltangle= Angle between Horizon and plane

                 SurfaceAzim= Surface Azimuth angle, that is angle between line normal to plane and North-South line measured from North, clock wise. 

                   Returns: Angle between sunrays and line normal to surface.