web metrics

Archive for October, 2007

Typical Celestial ModelHave you ever had to calculate the positions of astronomical objects? Orbital calculations relative to an observer on the Earth require derivations and time-consuming solutions of spherical trigonometric equations. And yet, these kinds of calculations were accomplished in the days prior to the advent of calculators or computers!

For example, to find the zenith angle (angle to overhead) and azimuth (angle from North) of the sun at any day and time of the year for any location on Earth, the laws of spherical trigonometry produce the formulas below. Here the solar declination δ is a function of the solar longitude λ and ecliptic angle ε as shown in the figure to the left.

Typical Solar Calculations

These calculations can be automated today—but did I mention that these solutions were found before electronic calculators?

… or slide rules, or logarithms?

 … or trigonometric formulas? 

… or even algebra??

In fact, Vitruvius (ca. 50) and Ptolemy (ca. 150) provided mathematical and instrumental means of calculating the sun’s position for any hour, day, and observer location by the use of geometric constructions called analemmas (only indirectly related to the figure-8 analemma on globes). An important application of analemmas was the design of accurate horizontal and vertical direct and declining sundials for any observer location. These analemmas are awe-inspiring even today, and as the study of “Descriptive Geometry” has disappeared from our schools they can strike us as mysterious and wondrous inventions!

(more…)

Comments 7 Comments »

AnalemmaThis journal attempts to capture my occasional encounters with the technically elegant but nearly forgotten in the mathematical sciences—artistically creative works that strike me as particularly brilliant. These can be small, clever things (say, an algorithm for calculating roots), or they can be ingenious technical inventions of more general application, basically anything that makes me think ‘Wow, that’s neat!’ Think of pendulum clock escapements; of beautiful precision sundials, astrolabes and other antique scientific instruments; of music theory and instrument design; of early, desperate attempts to calculate logarithms and trigonometric values; of stereo photography and linkage mechanisms; of difference engines, trinary arithmetic and slide rules; of old map projections and vacuum tube op-amps.

Posts here are brief or not-so-brief essays of unusual things of this nature that I read or hear about, supplemented with references and some amount of research I typically do on these topics. Any longer papers that emerge (particularly on mental calculation and antique scientific instruments) will be placed in my main website area http://www.myreckonings.com. To avoid printing difficulties with this wide format, there will be a link to a PDF version at the end of each entry.

Comments on the posts are appreciated! A forum has also been added for discussing anything related to lost art in the mathematical sciences at http://www.myreckonings.com/forum. Also, feel free to use the Contact link to send me general comments or any ideas (or text!) for new topics.

Ron Doerfler

(The figure above is from Oronce Fine’s Second Book of Solar Horology, translated with interpretation by Peter Drinkwater)

Comments 5 Comments »