The importance of light in architecture cannot be overstated. Understanding the impact of natural light on architectural space is essential for architects. This understanding includes knowledge of the sun and its position relative to the geographic location. There is more to understand to this concept than just barely having the knowledge that sun rises in the east and sets in the west. Sun path diagrams or sun charts are projections of the sky dome onto a surface. Assessing the passage of sun across a site is important. There are a number of locally-produced tools that can help, but a site visit is still necessary to identify site-specific conditions such as the impact of a large tree.

The sun path, sometimes also called the day arc, refers to the daily and seasonal path the sun appears to follow across the sky as the earth orbits it and rotates.  Sun-path analysis predicts the daylight experience at any building plot, helping us to design and orientate a building to make the most of sunlight and solar gains. By analysing the impact of sun on a site as well as the building’s location, orientation, window placement, daylight access and other design features, designers can take full advantage of passive solar design features and increase the energy efficiency, comfort and value of the building. 

Solar charts and sun path diagrams have been devised as visual aids so that the solar position can be easily and quickly established for any hour in any day, to provide a valuable tool for designers and planners.
Sun path is adapted in solar design that architects use in the initial phase of designing process. Sun path diagram can tell you a lot about how the sun will impact the building throughout the year.
Sun path diagrams provide a broader overview of sun on a site as they map the path of the sun across the sky at different times during the day throughout the year. They can help establish the position of the sun relative to as it and can be used to determine the effect of shadows cast by buildings, trees and landforms in and around the site.

Sun path projections
The sun path projections are classified into three types – spherical, equidistant and stereographic
Spherical – in this method the radial distance from the centre is the cosine of the altitude angle. This un path diagram is utilized in making sun path 3d model.
Equidistant – in this graphic the radial distance is imply a linear factor of the altitude angle. Thus the relative change in radius between all angles is the same.
Stereographic – this graphic is a more complicated projection in which azimuth lines are first projected back to a reference point located at a distance of 1 radius beneath the circle centre. The point where each of these lines intersect the zero axis give the radial distance. 

HOW TO READ SUN PATH DIAGRAMS?
STEP 1: IDENTIFY THE MONTH
The first thing you need to do is locate your month on the chart. These will be the heavy solid lines running horizontally, though they are slightly curved. In terms of solar position, June and December are special month. At the Summer and Winter solstice the sun is at its highest and lowest point, respectively. These two months have their own lines. Every other month shares a line with its opposite month.

STEP 2: IDENTIFY THE TIME
These are represented by the heavy solid lines running vertically. They are also slightly curved

STEP 3: FIND THE ALTITUDE
The altitude is the height of the sun above the horizon. Sunrise is the first time during the day the altitude is above 0. Sunset is marked when it drops below 0. The sun is higher in summer than it is in winter and higher at mid-day than it is in the morning or the evening. Higher sun means higher altitude. The altitude is represented by the thin circles. 
This chart has a circle for every 10 degrees of altitude.

STEP 4: FIND THE AZIMUTH
The azimuth is the angle of the sun from some reference point. 99.875% of the time this reference point is North, at least for those of us that live in the northern hemisphere. 
To find the azimuth of the sun, draw a line from the centre to the outer edge of the chart, going directly through the sun position you marked.

What is Altitude and azimuth?
The position of the sun with respect to an observer is commonly represented by two angles – altitude and azimuth.
Altitude is the angle of the sun’s rays compared with the horizon. At sunrise and sunset, the altitude is zero, and in the southern hemisphere, the maximum altitude of the sun at any specific location occurs at solar noon on 21/22 December (longest days of the year).
Azimuth (sometimes known as bearing) is the direction of the sun as shown on a compass.

Reading the Sun Position (Step-by-Step)

1.    Locate the required hour line on the diagram. 
2.    Locate the required date line, remembering that solid are used for Jan-June and dotted lines for July-Dec. 
3.    Find the intersection point of the hour and date lines. Remember to intersect solid with solid and dotted with dotted lines. 
4.    Draw a line from the very centre of the diagram, through the intersection point, out to the perimeter of the diagram. 
5.    Read the azimuth as an angle taken clockwise from north. In this case, the value is about 62°. 
6.    Trace a concentric circle around from the intersection point to the vertical north axis, on which is displayed the altitude angles. 
7.    Interpolate between the concentric circle lines to find the altitude. In this case the intersection point sits exactly on the 30° line. 
8.    This gives the position of the sun, fully defined as an azimuth and altitude.