Site conditions, including the position of the sun, can come up on a few exams, specifically Programming & Analysis and Project Planning & Documentation. It's important to know how to read sun path diagrams because you may be asked to make a decision about how the building relates to the sun or where shadows might be on a certain date and time. This is a quick guide to how to read a standard sun path diagram, as well as a discussion of why I don't agree with the diagram presented in Sun, Wind & Light.

Our goal here is to identify the Altitude and Azimuth of the sun on August 21st at 10am. Altitude is the height of the sun above the horizon and azimuth is the angle of the sun, usually from the north, but may be reported from the South as well…this is where I disagree with Sun, Wind & Light, more on that later.

This question originated from my PPD/PDD Study Assignments Course.

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 months. At the Summer and Winter solstice the sun is at it's highest and lowest point, respectively. These two months have their own lines. Every other month shares a line with it's opposite month. That's right, the sun is in the same position at 9am on the 21st day of February as it is at 9am on the 21st day of October. The complete list of pairs is May/July, April/August, March/September (these are the Equinox months), February/October and January/November.

Find the solid line that represents August. It is the third one down from the center.

Step 2: Identify the TIME

Now we need to locate the correct time. These are represented by the heavy solid lines running vertically. They are also slightly curved. If you are unsure of where to read the time, notice that the line that says “noon” points straight South…and the sun is more or less directly South at 12pm. We are looking for 10am, it's the 2nd line over from the middle.

At this point you should MARK THE INTERSECTION of your month and your time. This is the position of the sun. We can now pull the altitude and azimuth from the chart.

 

 

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. Look for the 10°, 20°, 30°…at the top center of the chart moving down toward the middle. It is unlikely the sun position you marked will be exactly on one of these circles. That means you will have to interpolate the position. Draw your own circle around the center of the chart, making sure it goes directly through the sun position you marked.

In this example it looks like the altitude circle I drew is just over halfway between the 50° and 60° circles, so I would call the altitude 56°.

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. A typical compass will show the cardinal directions (N, E, S, W) and provide a direction line every 10 degrees. These are the thin lines radiating out from the center. You can read the direction/azimuth on the outer edge of the chart. North is 000, East is 90°, South is 180°, West is 270° and then of course you get every 10 dgerees in between.

To find the azimuth of the sun, draw a line from the center to the outer edge of the chart, going directly through the sun position you marked.

Here's where I find Sun, Wind and Light annoying and not entirely correct. According to their chart, you would read the Azimuth as 60°. BUT, if you were to provide that information to someone who didn't have access to this exact chart, they would most likely think you were talking about a position that was generally Northeast. Since referencing azimuth from the north is the standard if you were referencing it from the South you should specifically mention that. In our example, instead of saying the azimuth is 60° you should say it is “60° East of South” to make it known you are using South as a reference. If you want to be a normal person, you would say the azimuth is 120° because a normal person would report the azimuth from the North.

I was going to give SWL a pass, because maybe they were in the Southern hemisphere, except the entire chart is for 32° North Latitude, so a person using this chart would most certainly be referencing North.

Sun path diagrams: what does this mean for the ARE?

It means pay attention to the diagram! I did not encounter a question where I had to literally type in or multiple choose an altitude…I did have a few questions where you had to understand the sun position so you could figure out where shadows were. Unless you are specifically told otherwise, or the diagram only shows degrees from the South, you can assume you reference North. Good advice for the ARE and real life.

Can't read this blog because you're driving? I have a video you can watch instead!

QUESTIONS ABOUT SUN PATH DIAGRAMS

What about the rest of the days that are not shown? April 4th for example?

The chart shows the 21st of each month because the Solstices and Equinoxes fall on these days. If you want a specific day that's not the 21st you need to interpolate the sun path for that date. April 4th is 17 days away from April 21 and 14 days away from March 21, so it's just under halfway between the month lines for March and April, and slightly closer to the March line. See image below.

Note: Original question asked about June 5th. At this latitude you can see May and June lines are really close, so it's going to be more difficult to find an exact date, but it won't matter much either because the sun position is so similar already.

Sun path diagrams aren't the only thing you should be ready for one exams.

Additional Test Prep Tools: 

• ARE 5.0 Course – PPD (Free Resources)
• Free Study Plans for the ARE 5.0
• Hyperfine Blog – Latest Tips & News