I guess the actual date was yesterday. Ironically, the weather here has been May-like until yesterday, when it suddenly turned chilly again. Still, the hour has come when the warmer weather is sure to come.
So you know about Stonehenge, but here are five sites -- not all "ancient," in spite of the headline, in fact the majority Medieval -- built to align with the spring equinox. One of them is the Basilica San Petronio, which contains a feature that was used to help construct our modern calendar:
In 1575, cosmographer Egnazio Danti arrived in Bologna to teach mathematics and astronomy. In order to continue his work on the commission charged by Pope Gregory XIII with the development of a new calendar, he constructed a meridian line in San Petronia. The meridian line—an astronomical instrument invented by Danti—consisted of a small hole high on the wall of the church; the position of the spotlight created when the sun shined through the hole allowed Danti to define and analyze the sun’s position and movements. This technique was later used by Giovanni Cassini to confirm the elliptical orbital model proposed by Johannes Kepler.