Sunpath Diagrams

Sun path diagrams or sun charts are projections of the sky dome onto a surface. Two different types exist and may have advantages and disadvantages, depending on the intended use. Both types show the same information, but in a different form. The type ofdiagram is usually referred to by the projectionsused:

Cylindrical projection
Show the Sun's appearent path for an observer who is looking due South. Useful for conducting shading calculations, especially for high geographicalaltitudes. It is very confusion when the sun is high up in the sky, i.e. in tropical situations.
Polar diagram
The sky dome is projected onto a horizontal plane with the observer being in the center. Ideal for visualising the compass direction of the Sun at any point in time,especially at tropicallatitudes and during the summer months. Different ways of mapping the altitude angles may be used. The steregraphic projection is most commonly used and has been chosen for the diagrams below.
diagram

Learn more about the images in this form

By selecting different sites in the form above, we can observe how the site's latitudeaffects the sun path:

  1. The altitude angle between the sun's highest and lowest point in the sky at noon (summer and winter solstice resp.) is always 23.5°. This is due to the Earth's tilt against the plane on which it moved around the Sun.
  2. The solar altitude at the equinoxes is exactly between those two extremes.
  3. For a site located in the tropics between 23.5°N and 23.5°S, the sun will be in the North during thesummer and inthe South during the Winter.
  4. For a site located above the arctic circle at 66.5°N (this is for the Northern hemisphere; reverse for Southern hemisphere), the sun will not set during part of the summer and never rise during part of the winter months.
  5. It is only true for the equinoxes that the sun rises in the East and sets in the West (exactly, at least). During the summer, the sun rises North of East and sets North of West, in winter it rises South of East and sets South of West.