Astronomical questions

Questions related to the history of Astronomy and the periods displayed on the Antikythera Mechanism

English

What are the Sidereal, Synodic, Tropical, Anomalistic and Draconic months?

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What are the Sidereal, Synodic, Tropical, Anomalistic and Draconic months?

In simple terms these are the periods of time that it takes for the Moon to compete a cycle, traveling from one ‘observable’ reference point, back to the same point. Unfortunately there are a number of different frames of reference, from the perspective of the observer’ and indeed different reference points, and consequently each gives rise to a different type of ‘lunar’ month.

In summary these are:

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In detail:

Sidereal Month

Does it favor a Heliocentric, or Geocentric Universe?

English

Does it favor a Heliocentric, or Geocentric Universe?

In a word neither. The purpose of the mechanism is clearly to position 'heavenly bodies' with respect to the 'celestial sphere', with reference to the observer's position on the surface of the earth. In order to achieve this, the mechanism has to use a geocentric model. However this does not imply that the manufacturer favoured a geocentric model of the universe. In fact it was Aristarchos of Samos (310 - c.230 BC) who first proposed a heliocentric solar system in 297 BC.

What are the Lower Back Dials "Glyphs"?

English

What are the Lower Back Dials "Glyphs"?

The remaining fragments of the lower back dial contain 16 sets of characters which were inscribed within some of the 223 divisions of the spiral dial. Each set of characters or "glyph" consists of 4 to 10 characters. Nearly all the glyphs contain S (lunar eclipse, from SELHNH, Moon) or H (solar eclipse, from HLIOS, Sun). Some glyphs contain both lunar and solar eclipse. In each case the hour (after sunrise, or sunset) is given.

What is a Parapegma?

English

What is a Parapegma?

A ‘parapegma’ is precursor to the modern day almanac. Originally it was a table that related star phases and corresponding weather predictions. Early versions were carved on stone, and had holes next to the descriptions, marking each day. The peg could be advanced each day, and on appropriate days the associated inscription would 'predict' certain astronomical and meteorological events.

What does it tell us about Greek Astronomy?

English

What does it tell us about Greek Astronomy?

Without a doubt it tells us that both Ancient Greek astronomy and mathematics were very advanced. This has to be placed in perspective as part of Greek astronomy comes after the long scientific tradition of the Babylonians, who built up a remarkable collection of astronomical data and discovered the repetitive patterns in that data. The Greeks placed these data into a new perspective. As an indication of the astronomical knowledge represented by the Mechanism, consider the FAQs regarding the Metonic, Callipic, Saros, and Exeligmos Cycles.

What is the Sothic year?

English

What is the Sothic year?

The Sothic year originates with ancient Egyptians. Early Egyptian astronomers discovered that the start of the annual Nile floods coincided closely with the first visibility of the star Sothis, now known as Sirius, in the morning sky (known as the heliacal rising). It is likely that the Egyptian calendar year started on the date of this rising. The Egyptian year was divided into three seasons of four months each. Every month consisted of 30 days. At the end of the year, five additional days were added. Thus a year had 365 days.