Thursday, July 17, 2014

Planet Plotting

Happening upon this video advert for a $330,000 watch that has all the planets rotating in real-time, I thought about older artifacts with similar purpose. I know their names, but have difficulty remembering which is which. I mix up an orrery with an armillary with an astrolabe, and so on. To remind myself, and maybe others who suffer from the same problem, I've collected images of them, all together, to act as a memory aid.

Additional information on each is available at the links provided at each heading.

The Armillary Sphere

Variations are spherical astrolabe, armilla, or armil. A model of objects in the sky (in the celestial sphere), consisting of a spherical framework of rings, centered on Earth, that represent lines of celestial longitude and latitude and other astronomically important features such as the ecliptic. As such, it differs from a celestial globe, which is a smooth sphere whose principal purpose is to map the constellations.

The Orrery

An orrery is a mechanical model of the solar system that illustrates or predicts the relative positions and motions of the planets and moons, usually according to the heliocentric model. It may also represent the relative sizes of these bodies; but since accurate scaling is often not practical due to the actual large ratio differences, a subdued approximation may be used instead. Though the Greeks had working planetaria, the first orrery that was a planetarium of the modern era was produced in 1704, and one was presented to the Earl of Orrery — whence came the name. They are typically driven by a clockwork mechanism with a globe representing the Sun at the centre, and with a planet at the end of each of the arms.

The Astrolabe

An astrolabe (Greek:astrolabos, "star-taker") is an elaborate inclinometer, historically used by astronomers, navigators, and astrologers. Its many uses include locating and predicting the positions of the Sun, Moon, planets, and stars, determining local time given local latitude and vice-versa, surveying, triangulation, and to cast horoscopes. It was used in classical antiquity, the Islamic Golden Age, the European Middle Ages and Renaissance for all these purposes.

The Quadrant and Sextant
An astronomical quadrant is essentially a graduated quarter of a circle, set up to measure the altitude of celestial objects above the horizon. The graduations from 0 - 90° are on the circumference, or limb of the instrument, over which usually a sight or index arm moves. While the quadrant was a quarter of a circle, the sextant was a sixth of a circle (60°) and its smaller arc meant that it was often more portable than a quadrant.

 Hat-tip to Daily Mail
More on celestial navigation HERE.

I really ought to include in this list the ephemeris (plural ephemerides) - hardly an artifact, often in book form, or nowadays available online, it serves much the same purpose as some of the above: tables giving computed positions of Sun, Moon, planets and other celestial bodies for every day of a given period, past, present or future - weeks, years, centuries.


mike said...

Hey, you omitted software! I haven't calculated planetary placements from an ephemeris for at least the past 15 years...or ascendant and house sign-degree from a "Table of Houses". Those were the days...LOL. I'm still amazed by the instantaneous charts that a computer or website can generate. I've become so accustomed to it that it's now a bit of a drag to have to enter the name, birth day, birth time, and place, which takes all of about a minute.

There are several watchmakers producing extremely high-end timepieces for the 1%...these are based on the antikythera:

"This machine has the oldest known complex gear mechanism and is sometimes called the first known analog computer, although the quality of its manufacture suggests that it had undiscovered predecessors during the Hellenistic Period."

Twilight said...

mike ~ I did, I did! I was spotlighting "artifacts" though

an object made by a human being, typically an item of cultural or historical interest.

I suppose software will be an artifact in a few thousand years, but the label doesn't seem to fit right now. :-)
Software did cross my mind, straight after ephemeris did - but I decided to leave it at the early stuff, and for my friendly blog associate to include ;-)

I often use my ephemeris for a quick idea of where stuff was on a given date - and the online ephemerides are valuable for looking up ancient dates or dates in the far future.

I wouldn't know how to begin using any of those artifacts in the post, but someone, somewhere should make an effort to understand 'em because one day, when the grid goes down, when things go really askew - they might be the only methods left.