Solar Geometry - Introduction

The Solar Geometry Model

The solar geometry model takes input of date, time and location of an observer on the earth and returns information about the location of the sun. The model can work in two modes: as a single shot calculation which is carried out each time an input variable is changed or it can be set so to automatically increment time and will run continuously.

User Input

The model takes the following inputs:

The date
- a year in the range 1800 - 2100,
- a month
- the day of the month
The time of day:
- hour (24 hour clock),
- minute
Location on the earth
- latitude (degrees),
- longitude(degrees)
The orientation and tilt of the surface of any building

Model Output

The model provides the following outputs.

the altitude and azimuth (see figure below) of the sun at that time and location,
the geometry of the sun with respect to any specified building.
the length of a shadow cast by a 1 metre pole
tables and graphs of the monthly and diurnal variation of the solar altitude and azimuth

Interfaces

Four interfaces are included here:

A Calculation Applet:
This applet would be used by students needing access to the raw information generated by the algorithm. Architects might use this algorithm to work out how much direct sunlight individual parts of a building might receive - helping them to decide on appropriate window styles and shades. The calculation applet is available from: http://www.jelsim.org/content/applets/solar/solarexpert.html
Solar Graph:
For a more academic analysis of solar geometry, a more graphical applet may be produced. In this applet, the learner can alter the same variables (latitude, time of year) and see how it affects various plots - including solar altitude and solar azimuth. By interpreting the shapes of the graphs produced at different times and locations the learner can begin to build up an understanding of the relationship- asking questions such as 'what happens at the equator?' or 'what happens at the equinoxes?'. The graph applet is available from: http://www.jelsim.org/content/applets/solar/solargraphs.html
For the Novice:
Complex graphs may be beyond the novice user (a primary school child can also benefit from an understanding of solar geometry), so a novice applet can also be created. Here, the display is much more visual (an image of the sun passes across the sky), yet the applet is mathematically correct, so the learner can be asked to 'collect data' such as observing when the sun rises and sets at different times of the year. The novice applet is available from: http://www.jelsim.org/content/applets/solar/solarnovice.html
Supporting Project Work
These applets show how a single model can be used in a variety of ways - supporting different levels of learner, different styles of teaching and different objectives. Materials can also be contextualised and localised. A sundial applet has been prepared which takes the same algorithm and extends it to calculate shadow length, allowing learners to look at the solar altitude and how it affects shadow length.The sundial applet is available from http://www.jelsim.org/content/applets/solar/sundial.html

Whilst other interfaces can be created from the same model, simple amendments to the model could also be carried out. For instance, a move to simClasses would enable creation of an applet which allowed users to compare day length in different cities on the same graph.