Author: VoijaRisa

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Almagest Book VII: On the Poles of Precession

From the above, it has become clear to us that the sphere of the fixed stars, too, performs a rearward motion along the ecliptic, of approximately the amount indicated. Our next task is to determine the type of this motion, that is to say, whether it takes place about the poles of the equator or about the poles of the inclined circle of the ecliptic.

Now that Ptolemy has determined that precession does indeed happen at a rate that agrees with Hipparchus, he now asks whether that precession is happening in the same direction as the ecliptic or the celestial equator.

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Data: Stellar Quadrant Observations – 9/16/2022 (Gryphon’s Fest)

Gryphon’s Fest was this past weekend and since I was in charge of the event I wasn’t really focused on observing. However, Jupiter was nearing opposition Friday night, so I wanted to make sure I got some observations there. While that went well, there’s still something much bigger that happened there. Continue reading “Data: Stellar Quadrant Observations – 9/16/2022 (Gryphon’s Fest)”

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Data: Stellar Quadrant Observations – Lilies War (6/19-21/2022) & Saturn Opposition (8/22/2022)

Oof. I haven’t been posting much. This year has been busy. With the SCA starting up again, a lot of time and emotional energy has been spent on prepping for wars, new classes, competitions, and planning an event I’m running next month. Not much time for astronomy.

However, there has been some recent observing. Details below the fold. Continue reading “Data: Stellar Quadrant Observations – Lilies War (6/19-21/2022) & Saturn Opposition (8/22/2022)”

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Data: Stellar Quadrant Observations – 5/27/2022

The weather this year has been frustrating. Winter held on far longer than normal. While temperatures weren’t freezing in March and April, they stubbornly refused to get into a temperature range that would allow me to open the windows. Then, after a few nice days, it immediately jumped into the early summer. Needless to say, such turbulent weather is not good for observing and I’ve only been out twice this year1

However, temperatures have cooled back off and, should a clear night occur, it would be a quite pleasant night to observe. This past Friday, despite solid cloud cover all day, the weather reports said it should clear by around $8$pm, so I headed out to Danville with the quadrant to do some observing. Although there was some high humidity, an adjustment in how I select what objects to observe made this likely one of the most productive observing sessions I’ve yet had. Continue reading “Data: Stellar Quadrant Observations – 5/27/2022”

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Queen’s Prize 2022 – The Astronomical Epoch for Solar and (First) Lunar Models

Thanks to Corona, it’s been quite awhile since we’ve really had an Arts & Sciences competition here in Calontir. While we had a virtual Kingdom A&S in $2020$ the last one we had in person was Queen’s Prize in $2019$.

However, this past weekend we finally had another in person Queen’s Prize and I entered my latest paper revising Ptolemy’s models for use in the present day. My previous entry attempted to update the solar model but contained critical errors2. This was revealed when I started attempting to update the lunar model. Realizing that it was predicting solar positions that would have made the eclipses necessary to calibrate the lunar model impossible, I revisited the solar model and made the necessary corrections.

That, plus the first lunar model were included in this year’s entry which was rewritten using LaTeX for a smoother editing and reading experience as Google’s equation editor was rather poor. The paper ended up being $62$ pages (although roughly $45\%$ of that was front material and appendices) which was a lot to expect anyone to read. As such, I also created a TL;DR version for passerbys.

Continue reading “Queen’s Prize 2022 – The Astronomical Epoch for Solar and (First) Lunar Models”

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Almagest Book VII: On Precession

At the beginning of the last chapter, Ptolemy noted that the celestial sphere appears to have a rearward motion of its own known as precession of the equinoxes. This motion means that the position of the sun in the zodiacal signs slowly increase in advance as time passes. In particular, the sun was at the beginning of Aries in Ptolemy’s time, but since then has advanced such that today it lies near the beginning of Pisces.

We can see this mainly from the fact that the same stars do not maintain the same distance with respect to the solstical and equinocital points in our times as they had in former times: rather, the distance [of a given star] towards the rear with respect to [one of] the same points is found to be greater in proportion as time [of observation] is later.

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Almagest Book VII: Hipparchus’ Star Alignments

Ptolemy lays out the arrangements described by Hipparchus by going through stars in various constellations:

Stars in Cancer. [Hipparchus] records that the star in the southern claw of Cancer [α Cnc], the bright star which is in advance of the latter and of the head of Hydra [β Cnc], and the bright star in Procyon [α CMi] lie almost on a straight line. For the one in the middle lies $1 \frac{1}{2}$ digits to the north and east of the straight line joining the two end ones, and the distances [from it to each of them] are equal.

First, we should discuss the identification of the stars. The designations of the stars in the brackets are the modern Bayer designations first created in $1603$. For Ptolemy’s part, he described the positions of the stars based on how they should appear in the representation of the constellation. For example, we see him here describing α Cnc as the “southern claw of Cancer”. However, because the depiction of the figures in constellations is somewhat subjective, this leads to some ambiguity in which stars are which, making assessing the validity of Ptolemy’s statements somewhat difficult. Continue reading “Almagest Book VII: Hipparchus’ Star Alignments”