The Astrolabe.
[ILLUSTRATION OMITTED]The Astrolabe
by James E. Morrison
Published by Janus, 18 Kingsbridge Road, Rehoboth
Beach, DE 19971, USA
Paperback: xiv + 438 pages, 2007
Size: 21.3 x 27.7 x 3.5 cm
ISBN: 978-0-939320-30-1
Price: $60
Available from Amazon.com or the publisher email:
janus.astrolabe@verizon.net
Hardcover: 2008
ISBN: 978-0-939320-31-8
Weight: 1.7 kg
Price: $125
Available from S. D. Myers Publication Services, 180
South Street, Tallmadge, OH 44278 USA
email: Jeanette.Kilchenman@sdmyers.com
Signed copies are available from the publisher. See
also http://astrolabes.org/theastrolabe.htm
Astrolabes have an aura about them that generates fascination among people from all walks of life. Aficionados have ranged from the early English poet Geoffrey Chaucer, whose 'Treatise on the Astrolabe' of 1391 was written for a 10-year old boy, through the nineteenth-century pioneer of spectroscopic astronomy, William Huggins, to George Ellery Hale, the erstwhile promoter of giant telescopes. The attraction of astrolabes must stem from their beauty and collectability. Many of the surviving instruments exhibit exquisite workmanship that displays the most intricate detail and ornamentation.
The development of the astrolabe occurred in the Middle East and it acquired its present form around 900 AD. It reached Europe through Muslim Spain and retained its popularity and usefulness until about 1700. Its main applications were in navigation, timekeeping and astronomical computation. Besides being in part a planisphere, it could be used for making observations of the altitudes of stars. Though many of its features were designed for one specific latitude, various improvements over time made it into a more universal instrument.
The baseplate of the typical astrolabe is called the 'mater' (Latin for mother) and it has a rim, called the 'limb', engraved with time and degree scales. Attached to it is a plate engraved with a stereoscopic projection of sky coordinates appropriate to a particular latitude. Above this is attached a movable 'rete', a kind of openwork graticule bearing little curlicued pointers identifying the positions of the bright stars. The ecliptic is also shown, marked off with the Sun's longitude and the zodiacal signs. Above all these is the 'rule', a movable pointer which helps with finding the time. The mater can be suspended from a hook and its back is calibrated so that, with the aid of a sighting bar called the alidade, the altitudes of the Sun or stars can be observed. The whole instrument is held together by a central screw or pin.
The bulk of James Morrison's weighty and profusely illustrated work, The Astrolabe, is concerned with how the various parts of the instrument are laid out and constructed. He discusses the astronomical theory behind the designs and shows how to make templates and carry out the actual engraving. About half the book deals with planispheric astrolabes. Universal astrolabes, usable at any latitude are also covered. Other chapters treat quadrants, horizontal and more specialised instruments. The pages of the book are large in size and the printing is very clear and precise, allowing the illustrations to be reproduced and used as masters for constructing one's own astrolabes.
The reader has a choice of technical levels at which to become involved. Designs can be made using computer programmes already set out, or the reader can code a unique design, examples being given in QBasic and C++. It is also possible to generate printable Postscript files directly. Pre-prepared designs are available for northern hemisphere latitudes, but certain changes are required when adapting them to the southern hemisphere.
The author of this book is a retired engineer who held a variety of positions at IBM and also worked as a systems software consultant 'The Astrolabe' is clearly a labour of love. It will surely come to be regarded as the standard work on astrolabes for the modern enthusiast.
'The Astrolabe' ends with a set of drawings that can be copied and used for making an astrolabe.
Chapter Titles (abbreviated): The Astrolabe, A Concise History, The Stereographic Projection, The Planispheric Astrolabe, Front, Drawing the Plate, The Rete, The Rule, The Back, Sample Problems, Southern Latitudes, Calculation, Universal Astrolabes, The Saphea Arzachelis, Orthographic Astrolabes, De la Hire's Astrolabe, Quadrants, The Astrolabe Quadrant, The Prophatius Quadrant, Sutton's Quadrant, Horizontal Instruments, Astrolabe Variations, Astrolabe Clocks, Astronomical Background, Calculations, Computers and Astrolabes, Design Layout and Fabrication, Appendices, Glossary, Bibliography, Index.
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| Author: | Glass, Ian |
|---|---|
| Publication: | Monthly Notes of the Astronomical Society of Southern Africa |
| Article Type: | Book review |
| Date: | Dec 1, 2008 |
| Words: | 719 |
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