What is the Langley method?
Samuel Langley pioneered the measurement of sunlight for the Smithsonian Institution. He used BEER’S LAW to measure the EXTRATERRESTRIAL CONSTANT of sunlight at the top of the atmosphere without leaving the surface of Earth. Though the method is very simple, it gives surprisingly accurate results. Therefore, it has been used by atmospheric scientists for more than a century. Briefly, the Langley method requires that you make measurements of direct sunlight with a Sun photometer for half of a very clear day. You then make a graph which plots the natural logarithm (ln) of your measurements (on the y or upright axis) against the AIR MASS (on the x or horizontal axis) during each measurement. If the day was clear and you pointed the instrument directly at the Sun, the data points plotted on the graph will fall along or very near a perfectly straight line. Extending this line to where it crosses the y axis at an AIR MASS of 0 will give the ln of the extraterrestrial constant for the instrum
