Ancient Greek astronomy

thumb|upright=1.2|Andreas Cellarius's illustration of the Copernican system, from the Harmonia Macrocosmica

thumb|upright=1.35|Figure of the heavenly bodies – An illustration of a Ptolemaic geocentric system by Portuguese cosmographer and cartographer Bartolomeu Velho, 1568 (Bibliothèque Nationale, Paris)

alt=Planispheric Astrolabe made of brass, cast, with fretwork rete and surface engraving|thumb|upright=1.2|North African, planispheric astrolabe. Khalili Collections|Khalili Collection. thumb|upright|A modern astrolabe made in 2013, in Tabriz, Iran.

ancient analog computer designed to calculate astronomical positions

Urania ( ; ; meaning "heavenly" or "of heaven") was, in Greek mythology, the muse of astronomy and astrology. In ancient art, her attributes include the globe and the pointer.

model of objects in the sky

clock with special mechanisms and dials to display astronomical information

thumb|right|The gnomon is the triangular blade in this sundial.

period of very close to 19 years that is nearly a common multiple of the solar year and the synodic (lunar) month

model of planetary motion in which planets moved in a small circle which in turn moves around the Earth

Astronomy as practiced in the Hellenistic world of classical antiquity

assertion that the Earth is (at least approximately) spherical

thumb|250px|right|Philolaus believed there was a "Counter-Earth" (Antichthon) orbiting the "Central Fire" (not labeled) that was not visible from Earth. The upper illustration depicts Earth at night while the lower one depicts Earth in the day. The Counter-Earth is a hypothetical body of the Solar System that orbits on the other side of the Solar System from Earth, e.g. at the L3 Lagrange point of the Sun–Earth system. A Counter-Earth, or Antichthon (), was hypothesized by the pre-Socratic Greek philosopher Philolaus () to support his non-geocentric cosmology, in which all objects in the unive

Length of time

work by Archimedes

thumb|Graphic reconstruction of the dioptra, by Venturi, in 1814. (An incorrect interpretation of Heron's description)

in ancient cosmological models, rotating spheres made of aether in which the stars or planets are embedded

medieval name for an ancient astronomical instrument

Metaphysical description of part of the universe

250px|right|thumb|The basic elements of Ptolemaic astronomy, showing a planet on an [[epicycle (smaller dashed circle), a deferent (larger dashed circle), the eccentric (×) and an equant (•).]]

system

a period of 76 years

An exeligmos () is a period of 54 years, 33 days that can be used to predict successive eclipses with similar properties and location. For a solar eclipse, after every exeligmos a solar eclipse of similar characteristics will occur in a location close to the eclipse before it. For a lunar eclipse the same part of the earth will view an eclipse that is very similar to the one that occurred one exeligmos before it (see main text for visual examples). The exeligmos is an eclipse cycle that is a triple saros, three saroses (or saroi) long, with the advantage that it has nearly an integer number of

angle-measuring device used for astronomical purposes

In astronomy, an octaeteris (, plural: octaeterides) is the period of eight solar years after which the moon phase occurs on the same day of the year plus one or two days.

early astronomical instrument

instrument to determine the moment of the equinoxes

[[File:Bowl of Ahaz refracting scaphe sundial, by Georg Hartman, Nuremberg, c. 1525-1564 - Putnam Gallery - Harvard University - DSC07927.jpg|thumb|right|"Georg Hartmann, German, 1525-1564, Bowl of Ahaz [Refracting scaphe sundial], Nuremberg, 1548, Brass Collection of Historical Scientific Instruments, Department of the History of Science, Harvard"]] The scaphe (; also known as a skaphe, scaphion (diminutive) or ) was a sundial said to have been invented by Aristarchus of Samos (3rd century BC). There are no original works still in existence by Aristarchus, but the adjacent picture is an image

astronomical cycle he created