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Derick Rethans: Analemmas

syndicated from on March 6, 2018

In a new post to his site Derick Rethans talks about "analemmas" and shows how to use PHP's own DateTime handling to determine the locations of the sun at different intervals (that's what an "analemma" tracks).

Last week I listened to an The Sceptics' Guide to the Universe where the word of the week was "But as I am currently starting to update the Guide to Date and Time Programming for a second edition, I was wondering whether I could create an analemma from existing PHP functions. Unfortunately, PHP only provides functionality to calculate when the Sun is at its highest point, through date_sun_info().

He includes an example of this function in use to determine the time the sun was at its zenith. While PHP by itself can't calculate the position, Derick remembered a PHP extension he wrote that could help: php-solarsystem. He includes some code using this functionality to iterate and locate the sun via its azimuth and altitude based on his choice of location (London). The result is a CSV export of data that he then drops in to gnuplot to create the graph of the analemma during that time.