Today is the summer solstice. This is the longest day of the year. And so it is that I made my way in the frying-pan heat to the Piazza of St. Peter’s Basilica for the one day of the year when I could shoot some interesting photos.
The obelisk casts a shadow on the stones of the piazza, of course, and the length of the shadow is measured by marble markers with dates and indications of the zodiacal signs. Most of the marks have two dates, since the shadow of the obelisk’s summit passes twice during the course of the year. Two of the markers have only one date. One is where the longest shadow of the year at the winter solstice extends and, as today, one where the shortest shadow of the year falls close to the obelisk itself.
I looked at the Vatican’s calendar today for the precise time of solar noon. Solar noon is not to be confused with "regular" noon. First, there is "daylight savings time" and then, the obelisk is some degrees east of the place with
"civil" noon occurs. The solar noon time on the calendar, which alway includes interesting astronomical information, gave the time for the solstice as 13:26. Knowing the Vatican, however, I decided to go early, both so as to fight through the hordes that were at the general audience and also to have time to clear chairs away from the marker if necessary. There were a couple other fellows there with cameras as well! It was good at I went, since solar noon actually occured at around 13:11. The Vatican calendar was wrong, which didn’t surprise me at all.
Here we go!
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Really intresting………..
Yes, very interesting!
Plinius mentions this obelisk in his Historia Naturalis: “Tertius (obeliscus) est Romae in Vaticano Gai et Neronis principum circo – ex omnibus unus omnino fractus est in molitione -, quem fecerat Sesosidis filius Nencoreus. eiusdem remanet et alius centum cubitorum, quem post caecitatem visu reddito ex oraculo Soli sacravit.” (Plin. Bk. 36, no. 74)
(This third obelisk [transported down the Nile and up the Tiber on specially constructed barges] was formerly dedicated by the Pharao as a fulfillment of a vow in thanksgiving for a restored eyesight after blindness.)
Interesting that Plinius (ibid) also mentions how obelisks were used to tell the time of the year:
“Divus Augustus addidit mirabilem usum ad deprendendas solis umbras dierumque ac noctium ita magnitudines, strato lapide ad longitudinem obelisci, cui par fieret umbra brumae confectae die sexta hora paulatimque per regulas, quae sunt ex aere inclusae, singulis diebus decresceret ac rursus augeresceret, digna cognitu res, ingenio Facundi Novi mathematici.”
Andrew: Did you know that Pliny told us about how one of the obelisks (the largest on in Rome) which was once the spina of the Circus Maximus was transported to Rome? It is in his section describing lentils! This was a digression for him, to be sure, but justifiable in that lentils were used as ballast on the ship used to transport the mammoth stone from Egypt to Rome. That ship, if memory serves, the largest in the Western ancient world, was eventually sunk by Claudius to serve as the foundation of a breakwater out at Ostia. The obelisk, after centuries, was rediscovered and moved up to St. John Lateran.
Also, I live but a stone’s throw from the obelisk Augustus Caesar used as the center of his sundial. I should shoot some photos of that and post them soon.