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 Printable Solar Assessment Tool Part 3

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Now that you have the Sun Finder both assembled and correctly oriented with geographic north and south, you can finally start using it. There is just one last thing you will need, the altitude and azimuth of the sun at several points as it moves across the sky.

Below, I will show you two places where you can find this info.

Getting the Sun's Path (With Online Sun Calculator)

Here is one website where you can get output for the sun's altitude and azimuth. http://www.gcstudio.com/suncalc.html

Simply fill in your latitude, longitude, and time zone offset along with the date you wish to generate the path of the sun. Next, just click the "Solar Data" button and a new window will pop up with everything you need.

This window gives a ton of information about the sun, and it might seem overwhelming if you've never seen it before. Don't worry though. You can ignore almost everything.

The only information that you will need is under the three columns with the headings "Local Civil Time," "Apparent Solar Altitude," and "Apparent Solar Azimuth."

Keep in mind that the altitude and azimuth angles are given in degree, minute, and seconds (DMS for short). An example would be, 119º49'16". This number is not in decimal degrees, which is what we need.

Converting from Degree Minute Second to Decimal Degree

It is fairly easy to convert a DMS number to decimal degrees mentally if you're not too concerned with it being 100% accurate. For this, we'll just completely ignore the "arcsecond" portion of this number. This is the part of the number which is followed by the double quotation marks, i.e. 16".

The next section of the number to deal with is the "arcminute" section. This is the part of the number which is followed by the single quotation mark, i.e. 49'. Essentially, an arcminute is just a one degree divided into 60 parts. This means that...:
15' = .25 decimal degree
30' = .5 decimal degree
45' = .75 decimal degree
60' = 1 decimal degree

Here are some easy examples of converting from DMS to decimal degrees.
13º30' = 13.5º
53º15' = 53.25º
5º45' = 5.75º
22º60' = 23.0º (Add the minute part to the decimal part here)

Here are a few more examples which require a little bit more thought. What you have to do with these is mentally round the arcminute portion of the number either up or down so that it will conveniently convert into decimal degrees. These are all approximate equalities.
13º55' = 14.0º
53º1' = 53.0º
5º12' = 5.25º
22º35' = 23.5º

Getting the Sun's Path (With Sketchup Plugin)

An alternative to the above site is to use the Sketchup Sun Position plugin that I wrote. You will need to download and install both Sketchup and the Plugin for this to work. Both are 100% free.

I personally think that using the plugin is easier than the above online calculator simply because it remembers your settings and it outputs the altitude and azimuth in decimal degrees. Both will get the job done though.

The information for saving the sun's path with the Sketchup Sun Position plugin can be found at the link.

Useful Dates

June 21 and December 21 (or Summer and Winter Solstice) are the longest and shortest days of the year. These are the two dates which you will probably find to be the most useful as they represent the times when the sun gets the highest and the lowest in the sky.

Another useful date is March 21. An equinox occurs on this day which represents the halfway point between the Solstices.

After the data is generated for each day, you may wish to either save the results to disk or print it out so that you can access it quickly for when you use the Sun Finder.

Finding the Sun with the Sun Finder

With the Sun Finder correctly oriented and the sun's altitude and azimuth in hand, you can try predicting the location of the sun.

For this example, we will first find where the sun is during the middle of the day so that we can be sure that we (OK, you :) have set it up correctly. If you go through these next steps and find that the Sun Pointer isn't pointing towards the sun, then you probably made a mistake somewhere and should figure out what it is before experimenting with other times of the year.

When I did this example, the sun's azimuth was -40 degrees and its altitude was 53.29 degrees.

To align the Sun Finder, I first turned it until the line marking south lined up with -40 on the azimuth protractor. Note: Always use the south mark when using the Sun Finder as it uses geographic south as the origin.

With the azimuth protractor aligned, I next set the altitude pointer at roughly 53.29 degrees.

If you did everything correctly, the Sun Finder should be pointing at the sun like you see in the picture below.

Easier way to see if the Sun Finder is Pointing at the Sun (Optional)

In the pictures above and below, you can see that I added a more accurate way to double check that the Sun Finder is pointing at the sun. This should help you verify that you are using it correctly. This is optional, but it only takes a second to do.

Notice how there is a drinking straw attached to the pointer part of the Sun Finder. Also notice how there is a square piece of cardboard attached to the drinking straw.

If you can see a shadow cast onto the cardboard by the drinking straw like in the picture below, the Sun Finder isn't pointing exactly at the sun. Note: This is an earlier version of the Sun Finder which is why it looks different in the pictures.

If there is absolutely no shadow at all though like in this picture, you can be certain that the Sun Finder is pointing directly at the sun. In all practicality though, you will probably have at least a little bit of a shadow cast by the drinking straw simply because it is hard to get it set up perfectly.

Laser Pointer Attachment (Optional)

You can also attach a laser pointer to the Sun Finder which can make it easier to see if the path between the Sun Finder and the sun is blocked. If the light from the laser hits a tree, for example, you can be certain that the spot the Sun Finder is located will be shaded when the sun has that altitude and azimuth.

The End

That pretty much covers it. I hope you find the Sun Finder to be useful.
Thanks for looking!

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