When is the summer equinox and why is it the longest day of the year?
The equinox isn’t until September 22 this year. Summer solstice, the longest day, is June 20th. Wikipedia: Of the many ways in which solstice can be defined, one of the most common (and perhaps most easily understood) is by the astronomical phenomenon for which it is named, which is readily observable by anyone on Earth: a “sun-standing.” This modern scientific word descends from a Latin scientific word in use in the late Roman republic of the 1st century BC: solstitium. Pliny uses it a number of times in his Natural History with the meaning it still has, but the word is in common use in other authors. It contains two Latin-language segments, sol, “sun”, and -stitium, “stoppage.” By this “standing” the Romans meant a component of the relative velocity of the sun as it is observed in the sky. Relative velocity is the motion of an object from the point of view of an observer in a frame of reference; for example, if it is true that seen from a space ship the Earth orbits the sun, it is al
