The Sun & Sky Monitoring
Station's Calculation Worksheets
Connecticut Analytical Corporation
I am sure that most, if not all, Society for Amateur
Scientists (SAS) members are well aware of the past
articles in The Citizen Scientist on atmospheric
studies, such as haze monitoring and solar observations.
Forrest M. Mims III has been a pioneer in utilizing
light emitting diodes (LED's) as an inexpensive alternative
to costly narrow band filters and photo detector combination
sensors to detect and monitor sunlight.
Forrest started his pioneering work using LED's as
sensitive narrow band sensors for haze monitoring
in 1989. This brilliant achievement (pun intended!)
has led to the realization of very inexpensive, yet
highly accurate and stable, atmospheric and solar
A while back, Dr. Sheldon Greaves wrote a review
of the Sun & Sky Monitoring Station for The
Citizen Scientist. If you are lucky enough to
have a Radio Shack nearby that still carries the Sun
& Sky Monitoring Station, then you should make
every effort to purchase one. Unfortunately, since
Radio Shack elected to stop producing the Sun &
Sky Monitoring Station after selling 12,000 of them,
you may not be able to find one.
Sun & Sky Monitoring Station
I have been influenced by the work
M. Mims III every since I was a kid. I have always
had an interest in electronics, and anyone who has
ever spent more than five minutes in a Radio Shack
while growing up is sure to have a copy of one of
his many electronics books. A small section in a bookcase
at home is devoted to my collection of Forrest's "Engineer's
Notebooks" and "Circuit Scrapbooks."
When I heard of the Sun & Sky
Monitoring Station, it was only a matter of time before
I got one. Having worked in the manufacturing industry
for over a decade, I know first hand what is involved
in coming up with new and innovative designs. Anyone
who has done any work in producing molded plastic
cases will have to admire the elegance and design
of the Sun & Sky Monitoring Station.
||Figure 1. The Sun & Sky Monitoring
||Figure 2. The Sun & Sky Monitoring
I was impressed with the compact housing
and integral compartments for the accessories. The 64-page
user manual/workbook is extremely well laid out and organized.
Forrest has written the user manual/workbook to be of use
to the most inexperienced beginner and the most seasoned professional
scientist. There are even several exams to test the reader's
In spite of all its many positive attributes,
the only negative comment I can make about the Sun & Sky
Monitoring Station is that it did not contain an accompanying
electronic spreadsheet. There are pages in the user manual/workbook
that are designed to be filled in by the user, but only once.
You would have to make a copy of the pages to continually
reuse them. Therefore, an electronic spreadsheet would greatly
enhance it usability.
After being extremely impressed while reading
through the user manual/workbook, and using the Sun &
Sky Monitoring Station, I took it upon myself to recreate
all the sections for data entry and graphing as an electronic
spreadsheet. Since I have Excel, I chose to create them in
that format. However, they can be easily imported into other
spreadsheet programs, such as Lotus 123. The Excel version
I chose to create them in is Excel 97, since I know that any
version after this will accept the spreadsheets without a
If you have already purchased a Sun &
Sky Monitoring Station, it is assumed that you have read through
the Sun & Sky user manual/workbook that accompanies it.
Each mode of operation has its own section in the user manual/workbook,
and I have copied that same methodology in the worksheets
that you can find here: Basic Sun
and Sky Worksheets and Advanced
Sun and Sky Worksheets. I did nothing more than
create an electronic version of Forrest's work.
The electronic worksheets are organized in
two separate categories, Basic and Advanced. The Basic worksheets
require only the Sun & Sky Monitoring Station, a watch,
and yourself. The data from the Sun & Sky Monitoring Stations
gnomon is all that is needed, along with the readout from
the LCD meter built into the Monitoring Station.
The Advanced worksheets require the user
to know their exact local latitude and longitude, along with
the exact time, and meteorological conditions (i.e.,
temperature, humidity, and barometric pressure). Although
more detailed information is required with the advanced worksheets,
all of the weather data can be added at a later time by using
archived local weather data for that specific day. For optimum
results, you can acquire appropriate meteorological instrumentation
to get very precise local measurements, but this is not required.
As stated before, the Sun & Sky worksheets
are laid out in two separate categories: Basic and Advanced.
An example of the difference between the two sheets is shown
in Fig. 3 and Fig. 4.
Figure 3. Basic Sun & Sky Monitoring Station Worksheet.
Figure 4. Advanced Sun & Sky Monitoring Station Worksheet.
In the Basic Worksheet shown in Fig. 3, the
air mass data are taken from the Sun & Sky Monitoring
Station's gnomon and are approximate. The Advanced Worksheet
in Fig. 4 calculates the exact air mass based on the observer's
local geographic coordinates and time. Notice the difference
in significant figures in the air mass given in the Basic
and Advanced Worksheets. The Basic Worksheet requires the
user to input this information as read from the Sun &
Sky Monitoring Station's gnomon, while the Advanced worksheet
precisely calculates this information for you.
Both sheets utilize the observer's local
time but have to be corrected to UTC (Universal
Coordinated Time) time. UTC time is expressed as the mean
solar time at the prime meridian (0 degrees longitude), also
known as GMT (Greenwich Mean Time). Since my local coordinates
are 5 hours west (EST) of the Prime Meridian, my UTC Time
Zone Correction is 5. It's up to the user if you choose to
observe daylight savings time or not, by adding or removing
an hour to the UTC correction. By ignoring daylight savings
time, you avoid “jumps” in your data.
When filling out a worksheet, one has to
stick to the convention of entering data in the appropriate
cell. All user entered data is color coded with green text
while all other cells contain formulas or results from other
calculations in black text. A screen shot of one of the worksheets
is shown in Fig. 5.
Figure 5. A screen shot of one of the
The cells with green text are for the user
to fill in, and the resulting calculations are displayed as
black text. The worksheets are coupled to live graphs. This
means the data points (see Fig. 6) are plotted on an accompanying
graph as the user enters the appropriate data.
Figure 6. Data points are plotted on a graph as data are entered
into the spreadsheet.
Each spreadsheet file contains the input
worksheet (user entered raw data), a graph (if required),
and blank worksheets devoid of any calculations. All sheets
can be printed out. However, when printing, one has to observe
one simple rule: always check the print preview and select
only the sheet(s) you are interested in. If you don't, then
twenty or thirty pages of calculations will be printed out.
NEVER select "All" in the print range when printing.
Figure 7. How to be sure only one page is printed.
Instead, as shown in Fig. 7, always select
one sheet to print out, and you should check to see that the
page margins are correctly laid out for one page. If you find
that one of the columns is missing, then adjust the margins
until it reappears.
Figure 8. Advanced Sun & Sky Monitoring Station worksheets
require that the user enter the local geographic coordinates
(latitude & longitude), as shown in this print preview
The Advanced Worksheets require that the
user enter their local coordinates (latitude & longitude).
If you have a portable GPS unit, then this is very simple.
If not, then try looking on the web. One place to look is
Naval Observatory. When entering coordinates, make sure
to convert them to their decimal form (see Fig. 8).
If you are unsure how to do this, I suggest
the following web site: http://home.online.no/~sigurdhu/Deg_formats.htm
Be sure to place the proper sign for the
latitude and longitude.
Latitude: North of the equator is positive
(+), South of the equator is negative (-).
Longitude: East of Greenwich, England, is
positive (+), West of Greenwich is negative (-).
When using the worksheets, you don't have
to add the plus sign for positive values. It's necessary only
to enter the negative sign. The calculations for the worksheets
are based on the previous work of Forrest M. Mims III ("TERC
VHS-1 SUN PHOTOMETER AEROSOL OPTICAL THICKNESS (AOT) SPREADSHEET")
and an Excel
97 spread sheet written by Keith Burnett.
When using these worksheets in Excel, it
is important that you have the Analysis
Toolpack installed as an Add-In for Excel. If you are
unsure how to do this, simply click on the Tools menu selection
in Excel, and scroll down to Add-Ins. Then check the check
box for the Analysis Toolpack. If you don't do this, then
some of the sheets will generate errors.
In addition to using the Sun & Sky Monitoring
Station for the applications Forrest has described in the
user manual, there are some additional creative uses for it.
For instance, if you are having problems with your IR remote
control, and you want to test it, simply switch on the Sun
& Sky Monitoring Station, select one of the two infrared
sensors (IR1 or IR2), and point the remote at the diffuser
panel. A working remote will show a voltage reading on the
LCD display, albeit unsteady and jittery.
If you have a bit of green-thumb in you,
then another possible application would be to check the photosynthetic
radiation (PAR) inside your home. If you have plants inside
your house, you might want to determine where the best lighting
conditions are. By following the procedure in the Sun &
Sky user manual/workbook for measuring PAR, you might find
that a window has been treated to block the red wavelengths
of light that are beneficial to plants.
Other possibilities include checking for
the presence of water vapor inside a sealed window, and checking
the effectiveness of emissivity coatings on windows. If you
have any ideas on innovative ways of using the Sun & Sky
Monitoring Station, send your ideas and results to TCS's
There are a few quirks that need to be mentioned.
When entering new data into a spreadsheet, some of the graph
information will get shifted. It is a simple matter of moving
the text back to the proper place before printing and saving
the worksheet. Notice the R2 (correlation coefficient)
text in the upper right section of the graph in Fig. 6. Be
sure to place the Green ET R2 value with the Green
ET, Red R2 with the Red ET, and so on.
Be sure to save each new worksheet as a new
name (Save As) when adding new data. You might want to keep
a copy of the original worksheets in a safe place. I will
be updating the worksheets at a later date to correct for
any unforeseen errors or bugs, since I have not had time to
run all combinations of positive/negative latitude, positive/negative
longitude, different time zones, etc.
If the spreadsheet (Advanced only) requires
you to enter a barometric pressure, then you MUST enter a
value – otherwise all your Air Mass results will be 0. If
you are unsure, use sea level (1013.2) as a baseline, and
check for the exact barometric pressure on a local weather
station. All barometric pressures are in millibars (mb).
You must never change or alter any of the
data values in black text; if you do this you are very likely
to get many errors throughout the worksheet. All sun azimuth
and altitude information is available to the user, but it
is not included in the main sheet. If you have the worksheet's
data entry sheet open (Advanced sheets only), then simply
scroll over to the right to see all related calculations.
I strongly advise against printing all this
unless you really hate trees! Thirty or forty sheets might
be printed. If you want to change some of the text headers
in the calculation section, that is okay. For instance, if
you live in California , then you would change the EST (Eastern
Standard Time) text header to PST (Pacific Standard Time).
This “text” change will not affect the calculations (see Fig.
Figure 9. Screen shot showing the time zone label.
As I mentioned earlier, these sheets were
designed for the Northern Hemisphere, but they should work
fine in the Southern Hemisphere. I did not have time to run
simulated tests. If any errors are found, I will try to make
And never forget this warning while making
measurements of sunlight: NEVER LOOK DIRECTLY AT THE
SUN!!! Always use good quality sunglasses when making
measurements with the Sun & Sky Monitoring Station.