Long before the Texas Instruments LEDcalculator , or even the slide normal , there was another type of computer : the astrolabe . The equipment involve its name , ultimately , from the Greek word astrolabos , or " star - pickings . “Astrolabeswere used primarily to make astronomical mensuration , typically of the altitude of celestial body , but shrewd philosopher , astrologist and leghorn devised hundreds of uses for the instrument . The astrolabe was , without a doubt , the slide formula of the Middle Ages .
Today , although computers and other technologies have replaced them in practical astronomical and maritime covering , astrolabe carry on to catch technophiles , skill historians and recreational sky watchers . Many educators employ the pecker in their schoolroom to instruct about the heavenly domain and how to plat and predict a mixed bag of astronomic phenomena , including sunrises / sunsets , moonrises / moonsets , star transits , retrogress motions and much more .
So what exactly is this astronomic instrument that compelled Geoffrey Chaucer to write about its structure and function in a fourteenth century treatise and then — intimately 620 years afterward — inspire Autodesk Fellow and software applied scientist Tom Wujec to demo aworking replicafor TEDGlobal ? On the next few pages , we ’ll explore both the nontextual matter and scientific discipline — as well as the rise and fall — of astrolabes .
The Cosmic Ecliptic: History of the Astrolabe
farsighted beforeclocksand calendar , humans turn to the Heaven to value time and point themselves on the planet . Ancient the great unwashed observed cycles/second related to the motions of Earth , the sun and the moon and used these cycles to determine the length of day , calendar month and years . They also watched the stars with great interest , arrange them into pictures — constellations — as a way to bring parliamentary law to the mad bedlam of the night sky .
Another organizing convention was the " celestial firmament , " an fanciful globe think to surround Earth . Like a traditional world , the heavenly empyrean have compass north and south poles , an equator and coordinates similar to latitude and longitude . To an observer on Earth ’s surface , stars existed as fixed item of luminosity on the interior of the welkin . The sunlight , moonshine and major planet were n’t fix to the empyrean , but propel around on a circular path known as the ecliptic .
Now imagine that you want to take the three - dimensional celestial sphere and project it onto a flat , two - dimensional surface . This was the fundamental job that confronted scholars like Hipparchus , who was assume in Nicaea in 180 B.C. Hipparchus kept punctilious disc of 850 stars , an activity that lead to the breakthrough of precession ( wobbling of Earth on its bloc ) and to a unique way of life of describe a star topology ’s location .
The Grecian astronomer was able to construct a map by imagining aperpendicular lineconnecting each star to a full stop on a carpenter’s plane equate to the woodworking plane of the Earth ’s equator . The map , which uphold the angular relationships among the stars , may have been the first object lesson of stereographic projection .
From Ancient Greece to the Islamic World
Claudius Ptolemy drew to a great extent from Hipparchus as he educate his magnum opus , the " Almagest , " and other books . In " Planisphaerium , " published in 150 A.D. , Ptolemy provides a complete verbal description , almost certainly based on ideas from Hipparchus , of the mathematical techniques expect to project point on the heavenly sphere . The book seemed to be a handbook to construct a working instrument , but no evidence exists suggest he actually built an astrolabe . He did , however , design and make the armillary orbit , a complex predecessor of the astrolabe
The first authorised account of what would become the modern , much - easier - to - use astrolabe came from Theon of Alexandria in 390 A.D. OK , so Theon did n’t actually build an astrolabe , but historians imagine he did bring home the bacon a full blueprint . And that design would travel all the way to the medieval Islamic world .
When Islamic astronomers pick up Theon ’s treatise on astrolabes , they saw their economic value immediately . They began making and using the musical instrument — and composing their own manual of arms . The first astrolabe template write in Arabic appeared in the eighth one C . By the eleventh hundred , the devices began appear in Muslim Spain .
From there , it was hop , skip and a jump into Christian Europe , where astrolabe help uranologist — and even talented poets like Chaucer — bring order of magnitude and stability to the night sky . They were an essential tool throughout the Middle Ages , until they became supplanted by newer , more specialized technologies , such as telescopes , sextant and pendulum pin clover .
Of Alidades and Almucantars: Anatomy of an Astrolabe
If you had an ancient astrolabe in front of you , whether it originated in 11th - one C Islam or 16th - century Europe , it would come with the same basic parts . Here they are , knead from the bottom of the legal instrument to the top :
Mater
The mater ( Latin for " mother " ) do as the base of an astrolabe . This circular plate , normally made of brass , extend about 6 inch ( 15 centimetre ) in diameter and a quarter - inch thick . Its center was hollow out out so one or more plate could baby-sit on top , nest in the Great Depression .
Limb
The flange of the mater , known as the tree branch , bore two scale — an inner scale for mensurate hours of the day and an out one for measuring degrees from 0 to 360 . A toilet bear a ring baby-sit above the noon marking , defining the top of the astrolabe and providing an attachment point . When he wanted to use the instrument , an uranologist would tie a rope through the ring and allow the twist fall straight down .
Plates
Next fall a serial of plates , with each home plate corresponding to a specific latitude . This was necessary because an observer located at the equator saw a different section of the dark sky compared to an observer , say , at mid - latitude . For the astrolabe to puzzle out the right way , it necessitate a plate specific to a give latitude .
Each plate came engraved with two kinds of circles . The first were roundabout of unvarying altitude known as almucantars , with the horizon being the most of import almucantar . The 2d were azimuths , which met the almucantars at ripe angles . The most important azimuth was the meridian .
Rete
The plexus ( sound like " pact " ) rested on top of the home plate . Modern retes are often made of transparent charge plate so you could see through them to the plates below . To get the same effect in the ancient world , astrolabe makers skip away large portions of the metal , leaving behind a skeletal - comparable hoop .
The rete was mark with a numeral of stars and several important constellations . As it rotated around a central rowlock ( the north celestial magnetic pole ) , the plexus demonstrate the daily apparent motion of the supernal area . The border of the rete contained an outmost scale divided into time of day and an inmost scale marked with days of the year .
Rule and Alidade
On some astrolabe , a clocklike hand called the rule , marked with declinations from -30 degrees to +70 academic degree , lay on top of everything . A bowling pin passed through the kernel of the pawn , holding all of the pieces together , but grant the pattern and the plexus to go around over the scale .
The back of the instrument contained a form of utilitarian plate and tabular array . All astrolabes included exfoliation for measuring angles and define the sun ’s longitude for any date . Many also had scale to solve simple trigonometry problems . An alidad also confiscate to the back , reserve a user to measure the ALT of a heavenly object .
Using an Astrolabe For Altitude Measurements
In the tenth century , Iranian stargazer ( and astrolabe adorer ) Abd al - Rahman al - Sufi compose a book claim 1,000 uses for an astrolabe . The Persian may have been exaggerating slightly , but in the bridge player of a skilled practitioner , the instrument could provide answer to many problem . With an astrolabe , astronomers could work out the position of object in heavenly sphere , the fourth dimension of Clarence Shepard Day Jr. ( or nighttime ) , the clip of year , the altitude of any target , different latitudes , and much more .
One of the easiest calculations to make with a universal astrolabe is the EL of an object above the horizon . The physical object could be anything — a tree , a mountain superlative , a star . To obtain its EL , take these steps :
Using an Astrolabe to Calculate the Sunset
Cool , huh ? Now get ’s say you need to employ the astrolabe to determine when the sun will set on a fussy day . Here ’s what you do :
More fun hand - on stuff next .
Telling Time With Your Amazing Astrolabe
Did you misplace yoursmartphone ? No worries , just draw in out your astrolabe to feel the time of day or night . During the day , you would base your calculations on the altitude of the sun . At night , you would utilize the ALT of a seeable principal . As an illustration , permit ’s walk through the gradation to shape the time of night :
The website of the Oxford Museum of the History of Science provide an excellentinteractive demoof this last recitation , using a reproduction of an ancient astrolabe . As it steps you through the operation , it also demonstrate the markings on the instrument ’s various scale of measurement .
Getting Your Own Astrolabe
If you ’re an astronomy buff , you ’ve probably already invest in a respectable telescope . Now you might want to add an astrolabe to your collection . The simple-minded matter is to buy an astrolabe that ’s ready to go right out of the box . you could get some antique astrolabes on eBay , although any pre-20th - century instrument will set you back some serious dough .
A unspoilt option is to buy a replica , which will give you an authentic ancient - astrolabe experience without the hefty monetary value ticket . you’re able to source a plane astrolabe and other variety on many websites .
Modern material do offer some advantages over establishment and pewter . A good blending of old and new schoolhouse comes from Janus , a Delaware - based caller behind several popular astrolabe resources . If you really need to kick it one-time school , you ’ll want to build your own astrolabe from scratch .
To get the full experience , start by register " A Treatise on the Astrolabe , " the first English - linguistic communication manual of arms on the instrument . James E. Morrison , the owner and creator of Janus and The Personal Astrolabe , has translated Chaucer ’s work out of Middle English into kinder , gentler language we all can understand ( a PDF of the translation is availablehere ) .
Building Your Own Astrolabe
To build an astrolabe you could habituate as you read the 14th - century treatise , your best bet is to depart with pre - existent templates . In " The History and Practice of Ancient Astronomy " ( Oxford University Press , 1998 ) , author James Evans provides a stage set of everlasting practice to make an astrolabe . You just photocopy the pattern onto paper ( or onto an acetate foil in the case of the rete ) , glue them down to tease stock , rationalise out the parts , perforate a hole in the plaza and tie up everything together using a bolt and nut . He specifically provides patterns for two elevation plates — Seattle and Los Angeles — but you’re able to also discover others in the body of the Christian Bible .
Another corking resource is a hand - on astrolabe bodily function developed by the Institute for Astronomy at the University of Hawaii . The site let in aprogramthat forecast a perfect set of astrolabe guide for any locating . Once you specify your localisation , the broadcast generates files you may save to yourcomputeror print out .
No matter which route you take , shop - grease one’s palms astrolabe or DIY , you ’ll possess your own rendering of the populace ’s first analog reckoner . And with it , you ’ll have a greater understanding of the nighttime sky — and a deeper connection to the world of ancient astronomy .
