Tracing the history of medieval astronomy
From the full scale plans we started cutting out pieces today.
First we cut out the arcs which will hold the scale. As noted previously, the idea was to have several to choose from so we could see which had the smoothest arc. If nothing else, it just reduced the amount of plywood we had laid out.
Continue reading “Instrumentation – The Great Quadrant: Day 2”
Now that we’ve introduced a bit about Ptolemy’s math we can take a look at his derivation of the chord tables. Exactly what those are we’ll get into later, once we have played around with some geometry that will hopefully clarify that issue.
To start, Ptolemy considers the following figure.
Continue reading “The Almagest – Book I: Special Angle Chords”
Before continuing into the math portion of this book, a brief interlude is necessary to explore how Ptolemy does his math. Chiefly, he uses the sexagesimal system which is a base 60 (as opposed to our base 10). The reason for this is that 60 has a large number of factors, which means it’s ideal for quick math since it you can make lots of fractions out of it.
This may sound odd at first, but consider that in some respects, it’s one we already use for telling time. There are 60 minutes to an hour and 60 seconds to a minute. In fact, that’s where the word “second” for measuring time comes from as it was the second division of the whole number. Continue reading “The Almagest – Book I: Sexagesimal & Ptolemy’s Math”
Work began today on the prototype of the great quadrant. I’d drawn up a set of plans for the quadrant arm last week (each box = 1″) so that’s where we started today (we being my father and I since he does construction and contracting professionally and has a workshop we can use).
To begin, we used a sheet of plywood to draw out a full sized set of blueprints. Mathematically, the most important parts of the entire structure is the arc which will display the scale, and that the pivot around which it rotates and from which the plum bob will hang is exactly in the center of the circle the arc lies on.
So to start, we measured the box in the upper left corner on the plywood, found the center, and screwed a long wood arm in the center. Holes were drilled in that arm at 36″ and 34″ from the center to draw the arc 2″ wide.
Continue reading “Instrumentation – The Great Quadrant: Day 1”
Ptolemy begins by drawing a distinction between practical and theoretical philosophy. The distinction is not defined here although Ptolemy gives “moral virtues” as an example of the former and “understanding of the universe” as an example of the latter. Likely, he is referring to Aristotle’s work, Metaphysics (Ptolemy almost never cited sources and Aristotle is the one name which is later cited which indicates how much Ptolemy drew from him), which defined three types of philosophy: The theoretical (knowledge for its own sake), the practical (morality), and the productive (works of utility and beauty). Continue reading “The Almagest – Book I: Introduction”
To help keep track of my working through the Almagest, below is an index of posts, grouped by book and chapter.
Continue reading “Almagest: Index”
The main thrust of this chapter is Kepler exploring the ghosts in the shell. The topic is centered on these two diagrams:
Continue reading “Astronomia Nova – Chapter 2”
As the long term goal of my project is to collect measurements in order to produce a star catalog and determine planetary orbits, this will obviously require some way to collect these measurements.
The master instrumentationalist whose data Kepler used was Tycho Brahe. He had numerous devices and their meticulous crafting and exceptionally large sizes allowed for the most accurate measurements of the age.
But for me, one stood out: Tycho’s Great Quadrant which is the one I’ll be modeling my own after.
Continue reading “Instrumentation – The Great Quadrant: Alignment”
Kepler begins the chapter by saying:
The testimony of the ages confirms that the motions of the planets are orbicular. Reason, having borrowed from experience, immediately presumes this: That their gyrations are perfect circles.
Kepler’s introduction to Astronomia Nova is somewhat of a lengthy ramble: 20 pages skipping from topic to topic and back again. In addition, he lays out somewhat of a preview of the structure of the book itself. But since we’ll be digesting that chapter by chapter anyway, I won’t discuss most of it and will instead sift through for the important parts. In addition, my summation won’t strictly follow the format Kepler does as I will try to group ideas on a similar topic.
The first important topic Kepler hits on is the
schools of thought among astronomers, one distinguished by its chief, Ptolemy… and the other attributed to more recent proponents [Copernicus], although it is the most ancient.