Sol – An apparatus that depicts pathways of the sun

Created by Jelle Reith, Sol is a custom made apparatus that can depict any position and any trajectory of the sun. Since the sun’s path changes every day, the exact path it takes through the sky depends not only on the date but also on the geographical location of the observer. Sol reveals the different pathways the sun takes from anywhere in the world.

Sol shows the position of the sun in terms of its azimuth and elevation. The azimuth is the angle between the true North and the sun’s vector on the horizontal plane and is expressed in degrees. In other words, if the sun is in the east the sun’s azimuth is 180° and when the sun is facing north its azimuth is 0°. The elevation describes the angle between the observer’s horizon and the sun. If the sun is directly overhead the elevation is 90°, when the sun is on the horizon the elevation is 0°.

“There are a number of things that influence the sun’s position in our sky. Most notably it is influenced by the earth’s rotation around its own axis and by the earth’s orbit around the sun. Secondly, the earth’s axial tilt is 23.5°, which causes the sun to shine on different latitudes at different angles throughout the year. This results in the different seasons. A few other factors, such as the earth’s wobble around its own axis caused by the uneven distribution of the earth’s mass, and the refraction of light as it passes through our atmosphere, influence the sun’s position minimally.”

Jelle Reith

To pinpoint the exact location of the sun the true solar time is needed. Due to the earth’s axial tilt and its elliptical orbit around the sun there is a difference between the true solar time and the local time. The local time might lead or lag the true solar time by up to sixteen minutes depending on the position of the earth. Jelle uses the equation of time to cancel out this effect and calculate the true solar time.

Lastly, there is one variable that Jelle has added with regard to the sun’s position in the sky. This is the user’s own geographical location on earth. Sol continuously recalculates and updates the sun’s path and current position by using an internal clock that tracks the time and date, and by using the geolocation set by the user.

Sol has a few different operating modes, each mode showing some additional data about the sun’s path. The sun’s current path and position will always be shown, regardless of the chosen operating mode.

Solstice and equinox – A solstice is when the sun reaches its highest or lowest elevation. The summer solstice occurs on the 21st* of June and the winter solstice is half a year later on the 21st* of December. Between the longest day (summer solstice) and the longest night (winter solstice) there is a day on which daytime and nighttime are of approximately equal length. This is called the equinox. The autumnal equinox is on the 23rd* of September and the spring equinox is half a year later on the 20th* of March. When this mode is selected Sol displays the path the sun would take on a solstice or equinox as well as its position throughout the day (date may vary depending on leap year, and other mitigating factors).

Orbits in +3, +6 and +9 months – When choosing this operating mode Sol shows the path the sun will be taking in three, six and nine months from now. The brightness varies depending on when the sun will take this path. The brightest path is the current one and the dimmest will be taken nine months from now.      

Solargraph – With this mode selected Sol will display the solargraph as well as the analemma of the sun. The solargraph shows all the pathways the sun will take in a year. The analemma is a figure eight form that you get if you were to document the sun’s position every day of the year at the same exact solar time and location.

Secondary location – When this mode is selected, Sol has the ability to keep track of a secondary sun path and position. The brightest path and position show the primary location and the dimmest path and position represent the secondary location. Both the primary and secondary location can be chosen by the user.

Hardware is designed using Eagle. Software written in C# using the arduino-ide framework. Hardware also includes 960 warm white leds produced by Cree, Microcontroller (ESP32-WROOM-32E), LED Drivers (IS31FL3733B) and two double sided PCB’s. Sliders of the interface are 3D printed.

The device is available for purchase via the link below.

Project Page | Jelle Reith