Stonyhurst disks

A Stonyhurst disk is a transparent circular grid with lines of solar longitude and latitude that can be overlaid on a solar image to reference the positions of sunspots. This system was originally developed at the Stonyhurst College observatory.Stonyhurst Disk Animation , Data and Activities for Solar Learning, eo.nso.edu,"Daily Sunspot Drawings at the 150-Foot Solar Tower", The 150-Foot Solar Tower at Mt. Wilson Observatory, UCLA

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