I can't remember if I've sent a notice of this before, but at least for the new members of this list, the Florida Solar Energy Center sells for $45 a new version 2.0 of software called SunPath. Although Sunpath is not primarily for sundials, and doesn't calculate sundial markings, it does calculate the altitude and azimuth angles of the sun for almost any latitude and longitude on earth. I've attached an ASCII text file provided with the program that is part of its HELP system, a file that describes the program in more detail. If you wish to order this program, please send $45 US payable to Florida Solar Energy Center to the Document Sales Office at the address shown below. -- Dr. Ross McCluney Florida Solar Energy Center 1679 Clearlake Road Cocoa, FL 32922-5703 USA 407-638-1000 VOICE 407-638-1439 FAX [EMAIL PROTECTED] EMAIL FSEC Web site: http://www.fsec.ucf.edu SunPath Designs: http://www.sunpath-designs.com -----------------------------------------------
ABOUT SUNPATH
INTRODUCTION SUNPATH is a computer program for DOS-based IBM and compatible personal computers. It calculates the position of the center of the sun in the sky at specified locations, dates, and times and outputs most results to the screen, a print file, and, if the user desires, to ASCII data files suitable for importing into graphic plotting programs. This new version (2.0) of the program includes a linked program, called PATHPLOT that per- forms high quality graphic plots of sunpath diagrams, using data files generated by SUNPATH. PATHPLOT is linked to SUNPATH so that the user can go back and forth between these two programs with only a few mouse clicks or key strikes. (PATHPLOT can also be run from the DOS command line prompt if desired by the user, as long as appropriate path data files from SUNPATH are avail- able for PATHPLOT to use.) The new version of SUNPATH supports mouse operations, if the mouse is installed on the computer before SUNPATH is run. A graphic monitor is still not needed to run SUNPATH, nor is one needed to run PATHPLOT. Without a graphic monitor, however, screen plots of the sunpaths are not possible. The user can generate graphic plots in Hewlett Packard Graphics Language (HPGL) with an *.HGL file extension default, or in PostScript with an *.EPS file extension default. Many modern laser jet and other printers can print these files directly, with- out user intervention. Many pen plotters read HPGL files. PATHPLOT has an option for direct printing to the computer's parallel printer ports LPT1, LPT2 or LPT3. Many graphic plotting and presentation programs can import HPGL and PostScript files and they can then be printed from these. Program options include determination of sunrise and sunset times, day length, and calculations of the path of the sun through the sky on any given day, including the solstices and equinoxes. Another option is available to output the sun's position in the sky at the same time each day for any interval of days through the year. This option is used, for example, to plot hourlines on sunpath diagrams plotted by the user in separate graphic plotting programs or by PATHPLOT when it creates these plots automatically. For more information about running the program and dealing with problems, select 'MISC. INFO.' from the main menu screen, the button just above the 'ABOUT...' button you used to get to this screen, or select/click the 'HELP' buttons found on many screens throughout the program. A separate printed paper manual is no longer provided with the program, in the interests of compactness and saving resources. In place of a printed manual, the program has been made to be fairly self-explanatory and has HELP buttons at several places and a special button on the main menu screen for miscellaneous additional information. Please send comments and/or questions to the Document Sales Office, Florida Solar Energy Center, 1679 Clearlake Rd., Cocoa, FL 32922-5703. Phones: Voice 407/638-1000, FAX 407/638-1010. THE SCIENCE BEHIND THE PROGRAM The core algorithm for calculating sun position was written originally in FORTRAN by Dr. Joseph Michalsky of the Atmospheric Sciences Research Center of the State University of New York at Albany. The subroutine used calculates the local azimuth and elevation angles of the sun at a specific location and time using an approximation to equations used to generate tables in The Astronomical Almanac (available from the U. S. Government Printing Office, Washington DC.) The approximate equations are reputed to be accurate to 0.01 degree of angle. Atmospheric refraction correction is added, so the sun position given by the program is the apparent position. For more information about the original algorithm, see Michalsky, Solar Energy Journal, Vol. 90, No. 3, pp. 227-235 (1988) and the errata to this article published later. (The atmospheric refraction correction can be seen as a slight wobbling of the sunpath and hourline curves on PATHPLOT plots near the horizon.) The resulting subroutine provides the solar coordinates based upon local civil time and has the equation of time imbedded in it in a way that makes showing this correction difficult. Solar time is not included in the sub- routine directly, but is calculated in the program by subtracting the hour angle from 180 degrees and dividing the result by 15, giving solar time in decimal hours. Local solar noon occurs at an hour angle of 180 deg. This fact is used to convert from solar time to civil time and vice versa. Special subroutines, called FINDSOLAR and FINDCIVIL, were developed, in the first case to calculate solar time directly using the above method and in the second case iterating between civil and solar times until the dif- ference between the desired solar time and the one resulting from the test value of the corresponding civil time is less than 0.0001 hour. Sunrise and sunset are defined by the U. S. Naval Observatory to occur when the apparent upper limb of the sun is coincident with the unobscured horizon at sea level. "Apparent" here means to include atmospheric refraction effects, giving the apparent position of the sun relative to the observer rather than the actual direction to the sun if no atmosphere were present. Since the diameter of the sun is approximately 0.535 degree, sunrise and sunset occur approximately when the center of the sun is below the horizon by one half of this angle, or at -.2675 deg altitude angle. To determine the time at which this condition occurs, the Michalsky algorithm is used in an iterative procedure repeatedly until a civil time is found such that the computed solar altitude angle is within 0.0005 degrees of this value. The number of iterations required to meet this tolerance is counted and reported along with the resulting sunrise and sunset times. THE PROGRAM AND ITS OUTPUT MODES In an attempt to make these complex equations available to a large and varied user group, SUNPATH was written to be relatively user-friendly, with a large main menu having several distinct options, including * single sun position calculation * a sun path calculation on a sequence of dates and times * tabulation of the solstices and equinoxes * determinations of sunrise and sunset times and day length * solar-to-civil time conversions (and vice versa) * a year-round timeline calculation option * a continuous, real-time, readout of sun position * dates and times when the sun is near a direction in the sky * comprehensive list of 233 cities in the U. S. and its territories, with their latitudes, longitudes, and time zones. In order to record the results of a session, including use of several of the main menu options and repeated runs of different menu options, a print file is created and several data files can be automatically created during a run of the program. When the program is terminated, the results of the session stored in the print file can be printed out on paper at the user's dis- cretion. It is also possible to print out any non-graphic screen to a printer using the "Print Screen" key on computers properly equipped and set up for this option. The data files are formatted to facilitate importing them into any of a variety of plotting programs including various spreadsheet programs, or specialized plotting programs such as PlotIT from Scientific Programming Enterprises and Sigma Plot from Jandel Scientific. For users who don't have access to these programs or don't wish to use them, SUNPATH has an option for generating output data files in a special format and running the companion program PATHPLOT to generate sunpath graphic plots in a variety of formats. PATHPLOT sends these plots to the screen of graphics-equipped computers and can be made to output graphic data files in either HPGL or PostScript (.EPS) formats. GRAPHICS SUNPATH is written in Microsoft VisualBASIC version 1.0 for DOS (VBDOS), which does not support printing of graphics screen plots. Programmer Jonathan Siegel overcame this limitation by using VBDOS to generate the drawing tools needed to put a complete sunpath graphic plot on the screen and to generate HPGL and PostScript commands needed to perform graphic plots on printers able to read these two file formats. Some graphic plotting programs can also read these formats, thereby enabling the user to annotate the plots with additional information as desired. Example annotations include the directional limits of the edge of a window or top of a wall, as viewed from a point on an opposite wall. Such markings could be used to indicate the dates and times when the sun will shine through the window or over the wall to the point. RUNNING IN MS WINDOWS Although SUNPATH and PATHPLOT are DOS-based programs, they can be run from within Microsoft's Windows environment by the use of supplied *.ico and *.pif files. Instructions are provided to enable this operation. EDUCATIONAL USES The program is intended for use in the fields of solar energy system design and operation, energy-efficient building design, city planning, outdoor photography, open-air stadium design, and remote sensing of earth resources. Many other uses are possible. Few people are fully knowledgeable about the apparent motion of the sun through the sky and the seasonal and yearly changes in this motion, or of the effects of this motion on their lives. It is suggested that the program can be used to overcome these deficiencies through its use in an educational context. Several exercises for the student can be suggested: 1. Plot the path of the sun through the sky at exactly 10:00 AM each day of the year, in both solar time and civil time. How do these plots vary with latitude and longitude? 2. At what latitude does the sun reach the zenith at solar noon on the summer solstice? 3. Plot the length of the day as a function of the day of the year from the winter solstice to the summer solstice at latitudes of 0, 20, 50, and 80 degrees. 4. If a sundial is designed to tell solar time accurately for each day of 1995, what will be the maximum error in the sundial's time over the next five years? 5. How do the sunrise and sunset azimuths on the summer and winter solstices vary with latitude? 6. Plot the time rate of changing solar altitude and azimuth angles for each hour of the day at your latitude and for the summer and winter solstices. POSSIBLE FUTURE IMPROVEMENTS Several possible future improvements in this program can be envisioned. These include: 1 Making a fully implemented Windows version. 2 Real-time outputs of solar altitude and azimuth angles to an RS-232 serial port. 3 Calculating and outputting the equation of time. Please indicate your interest in any of these revisions by contacting the Document Sales Office of the Florida Solar Energy Center at 1679 Clearlake Rd. Cocoa, FL 32922-5703 Voice:407/638-1000 FAX: 407/638-1010
