Happy equinox! The Sun will cross the celestial equator at 4:57 UT, heralding the first day of spring in the northern hemisphere. To honor the day, NASA released this cool image produced using solargraphy, a technique that follows the Sun’s annual trek across Earth’s sky.
In fact, three analemma curves were captured using a cylindrical pinhole camera by daily making three, separate, one minute long exposures for a year, from March 1, 2013 to March 1, 2014, on a single piece of black and white photographic paper. The well-planned daily exposures began at 10:30, 12:00, and 13:30, CET from a balcony looking south from the Kozanów district in Wrocław, Poland. That year’s two equinoxes on March 20 and September 22 correspond to the mid-points, not the cross-over points, along the figure-8 shaped curves. Apparent gaps in the curves are due to cloudy days. Two solid lines at the lower left were both caused by a timer switch failure that left the pinhole shutter open.