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Almagest Book II: Arcs of the Horizon between Equator and Ecliptic

Let us take as a general basis for our examples the parallel circle to the equator through Rhodes, where the elevation of the pole is 36º, and the longest day $14 \frac{1}{2}$ equinoctial hours.

Immediately starting the second chapter, we’re given a lot to unpack. First off, Ptolemy chooses to work through this problem by means of an example, selecting Rhodes, a city in Greece as the exemplar. I’m assuming that the “elevation of the pole” is the latitude, as Rhodes’ latitude is 36.2º. But what of these equinoctial hours? Continue reading “Almagest Book II: Arcs of the Horizon between Equator and Ecliptic”

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Data: Stellar Quadrant Observations – 7/27/18 (Mars Opposition)

One of the long term goals of this project is to collect enough data to derive the orbit of Mars. However, because Kepler didn’t know the orbit of Earth, he couldn’t use the observation on any given night. Instead, he only used observations from when Mars was at opposition1. This happened to be last night, so we packed up the quadrant and headed out.

Continue reading “Data: Stellar Quadrant Observations – 7/27/18 (Mars Opposition)”

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Thoughts on an Observing Team

When I first started thinking about how an observing team would work, I originally envisioned two people being necessary, with three being ideal. The thought was that one person would use the sight to locate the star as it crossed the meridian, a second would read the observation off the scale aloud, and a third would record it in a log book. If necessary the second person could do the writing.

This division of duties well matches an engraving Tycho had of his mural quadrant:

If we ignore the giant Tycho in the background as this is a heavily stylized image, we see the observer at far right sighting the star, one reading off the time, and a third recording the observation.

However, the past few days I’ve been working on a list of stars to observe and think it may be necessary for my purposes to have even more. Continue reading “Thoughts on an Observing Team”

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Data: Converting Alt-Az to RA-Dec – Example

In the last post, we derived equations to demonstrate that the right ascension (α) and declination (δ) of an object can be gotten by knowing four other variables: altitude (a), azimuth (A), sidereal time (ST), and latitude (φ).

In this post, I’ll do an example of using these equations to do just that. For my data, I’ve jumped into Stellarium and selected Altair3 as it’s a nice bright star that I’ll certainly be observing.

Continue reading “Data: Converting Alt-Az to RA-Dec – Example”