Month: December 2020

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Data: Stellar Quadrant Observations – 12/9/2020

Yesterday, the highs here in Three Rivers climbed into the 60’s. It’s December. This isn’t normal. But the weather was absolutely stunning and not even the sort that whips around to bone-chilling cold the next day as it was again in the 60’s today. This brief stability in the weather brought clear, calm skies, so despite it being a work night, I knew I needed to get out to observe.

Fortunately, with it getting dark so early, I could observe for several hours and still be home by a reasonable hour, even if I headed out to the further site I like observing at, Danville Conservation Area. And boy what a night it was! Continue reading “Data: Stellar Quadrant Observations – 12/9/2020”

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Almagest Book V: Calculation of the Lunar Position

It’s been awhile since I’ve done an Almagest post so quick recap. In Book IV, we worked out a first model for the moon, which was a simple epicycle model inclined to the plane of the sun’s sphere. In this book, Ptolemy showed us that this model was insufficient as the moon’s speed varies more than should predict and so we added an eccentric as well as having the center of the eccentre rotate around the observer. Finally, we introduced the concept of a “mean apogee” which is the position on the epicycle we’ll need to measure from in order to do calculations.

That’s been a lot, but with all of this completed, we should now be able to use it to calculate lunar positions which Ptolemy walks us through in this chapter. Unfortunately, he does this in the form of a generic prescription of steps instead of a concrete example. Fortunately, Toomer provides an example1 that I’ll use to supplement Ptolemy’s narration. Continue reading “Almagest Book V: Calculation of the Lunar Position”