Wednesday, October 7, 2015

Moon: Posidonius

Oblique view of Posidonius from Apollo 15.
A tightly convoluted sinuous rille crosses the raised floor of the crater, turns back,
and follows the rim to a low point in the western rim.
NASA - Apollo 15 Hasselblad camera image. The original image should be public domain it is a work of the U.S

The scarred face of the Old Man in the Moon invites us to learn more about the great astronomers of Antiquity and of Medieval time.

Posidonius Crater
Posidonius is a lunar impact crater that is located on the north-eastern edge of Mare Serenitatis, to the south of Lacus Somniorum. The crater Chacornac is attached to the southeast rim, and to the north is Daniell.
The rim of Posidonius is shallow and obscured, especially on the western edge, and the interior has been overlain by a lava flow in the past. The crater ramparts can still be observed to the south and east of the crater rim, and to a lesser degree to the north.
There is a smaller, semi-circular rim of a concentric, flooded crater within the main rim, offset towards the eastern edge. There is no central peak, but the floor is hilly and laced with a rille system named the Rimae Posidonius. The floor is also slightly bulged due to the past lava uplift, which also likely produced the complex of rilles. The northeast rim is interrupted by the smaller crater Posidonius B. Within the crater rim, offset just to the west of center is another smaller crater Posidonius A.

Posidonius of Apamea
Posidonius (Greek: Ποσειδώνιος, Poseidonios, meaning "of Poseidon") "of Apameia" (ὁ Ἀπαμεύς) or "of Rhodes" (ὁ Ῥόδιος) (c. 135 BC – c. 51 BC), was a Greek Stoic philosopher, politician, astronomer, geographer, historian and teacher native to Apamea, Syria. He was acclaimed as the greatest polymath of his age. His vast body of work exists today only in fragments.
Writers such as Strabo and Seneca provide most of the information, from history, about his life.

Some fragments of his writings on astronomy survive through the treatise by Cleomedes, "On the Circular Motions of the Celestial Bodies", the first chapter of the second book appearing to have been mostly copied from Posidonius.

Posidonius advanced the theory that the Sun emanated a vital force which permeated the world.

He attempted to measure the distance and size of the Sun. In about 90 BC Posidonius estimated the distance to the sun to be 9,893 times the Earth's radius, which was still too small by half. In measuring the size of the Sun, however, he reached a figure larger and more accurate than those proposed by other Greek astronomers and Aristarchus of Samos.

Posidonius also calculated the size and distance of the Moon.

Posidonius constructed an orrery, possibly similar to the Antikythera mechanism. Posidonius's orrery, according to Cicero, exhibited the diurnal motions of the sun, moon, and the five known planets.

Cosmic philosophy
He accepted the Stoic categorization of philosophy into physics (natural philosophy, including metaphysics and theology), logic (including dialectic), and ethics.
These three categories for him were, in Stoic fashion, inseparable and interdependent parts of an organic, natural whole. He compared them to a living being, with physics the meat and blood, logic the bones and tendons holding the organism together, and finally ethics – the most important part – corresponding to the soul.
His philosophical grand vision was that the universe itself was similarly interconnected, as if an organism, through cosmic "sympathy", in all respects from the development of the physical world to the history of humanity.

Excerpts from Wiki texts have been incorporated into the blog as kinds of abstracts for reader's convenience. By clicking the links much more can be learned about these subjects.

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