The position of the Sun in the sky at any time of the day on any day of the year can be read directly from a Sun-Path Diagram. The animation below details the process required to find the position of the Sun at 9:00am on the 1st of April. If the animation stops, simply hit the Refresh or Reload button at the top of your browser.
Polar Sun-Path Diagrams
Follow the steps below to read the Sun position from a stereographic sun-path diagram:
- Step 1 - Locate the required hour line on the diagram.
- Step 2 - Locate the required date line, remembering that solid are used for Jan-Jun and dotted lines for Jul-Dec.
- Step 3 - Find the intersection point of the hour and date lines. Remember to intersect solid with solid and dotted with dotted lines.
- Step 4 - Draw a line from the very centre of the diagram, through the intersection point, out to the perimeter of the diagram.
- Step 5 - Read the azimuth as an angle taken clockwise from North. In this case, the value is about 62Ã‚Â°.
- Step 6 - Trace a concentric circle around from the intersection point to the vertical North axis, on which is displayed the altitude angles.
- Step 7 - Interpolate between the concentric circle lines to find the altitude. In this case the intersection point sits exactly on the 30Ã‚Â° line.
This gives the position of the sun, fully defined as an azimuth and altitude.
Cartesian Sun-Path Diagrams
In cartesian co-ordinates, the azimuth is plotted along the horizontal axis whilst the altitude is plotted vertically. The date and time values are first located in exactly the same way as in the Polar sun-path diagram. Once the date-hour intersection point is found, reading off positions is simply a matter of projecting vertically and then horizontally onto the two axis, as shown in the animation below.
Follow the steps below to read the Sun position from a cylindrical sun-path diagram:
- Step 1 - Locate the required hour line on the diagram.
- Step 2 - Locate the required date line, remembering that solid are used for Jan-Jun and dotted lines for Jul-Dec. In these diagrams, the highest altitude line at noon is always in midsummer (either 1st July or 1st Jan, depending on hemisphere). Each other line represents the 1st of each month, solid Jan-Jun, dotted Jul-Dec.
- Step 3 - Find the intersection point of the hour and date lines. Remember to intersect solid with solid and dotted with dotted lines.
- Step 4 - The azimuth is given by reading off the horizontal axis. In this case, the value is about 62Ã‚Â°.
- Step 5 - The altitude is given by reading off the vertical axis. In this case the intersection point sits almost exactly on the 30Ã‚Â° line.