Author: VoijaRisa

Posted on

Almagest Book III: Hypotheses for Circular Motion – The Two Hypotheses

So far in Book III, we’ve been looking at the mean sun1. However, the sun’s motion along the ecliptic is not even. In other words, its speed along the ecliptic is not constant. This poses a problem because, to Ptolemy:

the rearward displacements of the planets2 with respect to the heavens are, in every case, just like the motion of the universe in advance, by nature uniform and circular. That is to say, if we imagine the bodies or their circles being carried around by straight lines, in absolutely every case the straight line in question describes equal angles at the center of its revolution in equal times.

Here, Ptolemy states that he accepts uniform circular motion as true. So the question becomes how can something moving at a constant speed appear to have not constant speed? Continue reading “Almagest Book III: Hypotheses for Circular Motion – The Two Hypotheses”

Posted on

Data: Stellar Quadrant Observations – 8/24/19

Life has been eating me pretty heavily lately so I haven’t had any time to work on the Almagest, and barely any time to observe. But last weekend, I took the quadrant to Baroness Wars over in the Midrealm. The location wasn’t all that great. The dark sky map said it was like being in the suburbs of St Louis, and the fact that they left some lights on illuminating a racetrack or something next to the county fairgrounds we were in also sucked, but I was still able to get a few observations in over the two nights I was there.

Continue reading “Data: Stellar Quadrant Observations – 8/24/19”

Posted on

Data: Stellar Quadrant Observations – 7/27/19

Last month, I came across this dark sky finder website. Unsurprisingly, dark skies in the Eastern half of the US are fairly hard to come by. However, Mark Twain National Forest in southern Missouri puts a significantly large dent in light pollution that much of the surrounding area is quite dark. Sadly, as the name suggests, the forest doesn’t have many clear sites suitable for astronomical observing, but I was able to find a campsite that’s part of the Rocky Creek Conservation Area that what looked to be a large field based on Google Maps that sat in the dark area.

This weekend I found someone to take over my herald duties to Their Majesties and made the 2.5 hour drive to check it out. Continue reading “Data: Stellar Quadrant Observations – 7/27/19”

Posted on

Statistical Review of the Great Quadrant

Kingdom A&S is in just over a month and coincidentally falls on the one year anniversary of first light of the quadrant. Originally, I’d planned to do a deep dive statistical review of the quadrant, looking at sources of error, but this would be a modern mathematical review of an instrument that isn’t entirely period. Discussing it with friends, we decided it was a little too meta/degrees of separation.

Instead, I’ll do a blog post! So if you really want to get into the accuracy on the quadrant, hold on because I’m about to get mathy. Continue reading “Statistical Review of the Great Quadrant”

Posted on

Data: Stellar Quadrant Observations – Lilies War

This past week was Lilies War, north of Kansas City. With a bit of packing tetris, I was able to fit the full quadrant along with most of my camping gear3 to attend. Despite Lilies being traditionally extremely hot4 and stormy, the weather was quite nice this year with highs in the 70’s most days and lows in the 50’s5. This unseasonably cool weather did bring some storms, but nothing like what we’ve experienced the past few years. Yet between storms I was able to get in a few nights of observing, getting in observations of 59 stellar targets, 26 of which are new to the catalog.

As always, data below the fold. Continue reading “Data: Stellar Quadrant Observations – Lilies War”

Posted on

Data: Stellar Quadrant Observations – 5/31/19

Yesterday promised a beautiful night. Temperatures in the low 70’s falling to mid 60’s overnight, clear skies, and no moon. So I packed up the quadrant and met Hugo at Brommelsiek to do some observing.

Unfortunately, despite the skies being clear, there was a lot of humidity and spotting stars past 3rd magnitude was challenging. Hugo was only able to stay a little over an hour, but I stayed out almost 4, and only had 15 observations at the end of the night.

As usual, details below the fold. Continue reading “Data: Stellar Quadrant Observations – 5/31/19”

Posted on

Almagest Book III: Table of the Mean Motion of the Sun

To help us determine where the sun is on a given date, Ptolemy sets out a table to allow us to more quickly look this up instead of needing to calculate how far around the ecliptic the sun has moved. This table is very similar to another set of tables Ptolemy would produce later: The Handy Tables. However, there are some notable differences between this table and the Handy Tables. Continue reading “Almagest Book III: Table of the Mean Motion of the Sun”

Posted on

Almagest Book III: On the Length of the Year

If I were to summarize the books of the Almagest so far, I’d say that Book I is a mathematical introduction to a key theorem6 and an introduction to the celestial sphere for the simplest case of phenomenon at sphaera recta. In Book II, much of that work is extended to sphaera obliqua, but in both cases, we’ve only dealt with more or less fixed points on the celestial sphere: The celestial equator, ecliptic, and points within the zodiacal constellations based on the immovable stars.

But the ultimate goal of the Almagest and my project isn’t to study the unchanging sky; it’s to understand the changing sky: The sun, moon, and planets. Ptolemy decides to start with the position of the sun is a prerequisite to understanding the phases of the moon, and planets are more complicated with their retrograde motions. And to kick off the investigation of the motion of the sun, Ptolemy first begins by carefully defining a “year” noting

when one examines the apparent returns [of the sun] to [the same] equinox of solstice, one finds that the length of the year exceeds 365 days by less than $\frac{1}{4}$-day, but when one examines its return to the fixed stars, it is greater [than 365 $\frac{1}{4}$-days].

Continue reading “Almagest Book III: On the Length of the Year”