Tracing the history of medieval astronomy
Now that we’ve worked out the distance to the moon at the time of the observation, we can put this information back into our lunar model diagram to work out the true scale. We’ll begin with a drawing of our lunar model at the time depicted:
Continue reading “Almagest Book V: Scale of the Lunar Model”
So far, we’ve stated that the effect of the second anomaly is to magnify the first anomaly. In the last chapter, we worked out how much larger. Since this second model works by bringing the moon physically closer and further by offsetting the center of the lunar orbit with an eccentric and having that eccentre orbit the Earth, we can determine how far that center must be. In other words, the eccentricity of this second anomaly. Continue reading “Almagest Book V: Second Anomaly Eccentricity”
Now that we’ve laid out how the two hypotheses work and explored how they sometimes function similarly, it’s time to use one of them for the sun. But which one? Or do we need both?
For the sun, Ptolemy states that the sun has
a single anomaly, of such a kind that the time taken from least speed to mean shall always be greater than the time from mean speed to greatest.
In other words, the sun fits both models, but only requires one. Ptolemy chooses the eccentric model due to its simplicity.
But now it’s time to take the hypothesis from a simple toy, in which we’ve just shown the basic properties, and to start attaching hard numbers to it to make it a predictive model. To that end, Ptolemy states,
Our first task is to find the ratio of the eccentricity of the sun’s circle, that is, the ratio of which the distance between the center of the eccentre and the center of the ecliptic (located at the observer) bears to the radius of the eccentre.
Continue reading “Almagest Book III: On the Anomaly of the Sun – Basic Parameters”
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”
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.