Parallax in the park

This article describes a parallax experiment performed by undergraduate physics students at Queensland University of Technology. The experiment is analogous to the parallax method used in astronomy to measure distances to the local stars. The result of one of these experiments is presented in this paper. A target was photographed using a digital camera at five distances between 3 and 8 metres from two vantage points spaced 0.6 m apart. The parallax distances were compared with the actual distance measured using a tape measure and the average error was 0.5 ± 0.9 %.

The works of Plato. A new and literal version chiefly from the text of Stallbaum ...

Vol. I translated by Henry Cary, vol. II, by Henry Davis, vols. III-VI, by George Burges.

The works of Plato /

v. 1. The Apology of Socrates, Crito, Phaedo, Gorgias, Protagoras, Phaedrus, Theaetetus, Euthyphron, and Lysis -- v. 2. The Republic, Timaeus, and Critias -- v. 3. Meno, Euthydemus, The sophist, The statesman, Cratylus, Parmenides, and the Banquet -- v. 4. Philebus, Charmides, Laches, Menexenus, Hippias major, Hippias minor, Ion, First Alcibiades, Second Alcibiades, Theages, The rivals, Hipparchus. Minos, Clitopho, The epistles -- v. 5. The laws -- v. 6. The doubtful works ... with lives by Plato by Diogenes Laertius, Hesychius, and Olympiodorus; introductions to his doctrines, by Alcinous and Albinus; the notes of Thomas Gray, and a general index.

Tabulae frisicae lunae-solares quadruplices : è fontibus Cl. Ptolemaei, Regis Alfonsi, Nic. Copernici, & Tychonis Brahe, recens constructae /

Mode of access: Internet.

Platonis Opera quae feruntur omnia : ad codices denuo collatos /

Text in Greek; introd. and notes in Latin.

Platon's werke einzeln erklärt und in ihrem zusammenhange dargestellt,

Vol. 2-3, Erfurt, C. Villaret.

Platonis Opera omnia...

The editions vary.

Platonis opera quae feruntur omnia.

No more published.--cf. Klussmann and Bibliothèque Nationale catalog.

The works of Plato : a new and literal version, chiefly from the text of Stallbaum /

Vol. 1 translated by Henry Cary; vol. 2 translated by Henry Davis; vol. 3-6 translated by George Burges.

Opera quae feruntur omnia. Ad codices denuo o collatos,

Each vol. has also special t.-p.

The Riemann sphere in GeoGebra

The stereographic projection is a bijective smooth map which allows us to think the sphere as the extended complex plane. Among its properties it should be emphasized the remarkable property of being angle conformal that is, it is an angle measure preserving map. Unfortunately, this projection map does not preserve areas. Besides being conformal it has also the property of projecting spherical circles in either circles or straight lines in the plane This type of projection maps seems to have been known since ancient times by Hipparchus (150 BC), being Ptolemy (AD 140) who, in his work entitled "The Planisphaerium", provided a detailed description of such a map. Nonetheless, it is worthwhile to mention that the property of the invariance of angle measure has only been established much later, in the seventeenth century, by Thomas Harriot. In fact, it was exactly in that century that the Jesuit François d’Aguilon introduced the terminology "stereographic projection" for this type of maps, which remained up to our days. Here, we shall show how we create in GeoGebra, the PRiemannz tool and its potential concerning the visualization and analysis of the properties of the stereographic projection, in addition to the viewing of the amazing relations between Möbius Transformations and stereographic projections.