This past week, I started a new job which allows me to sleep in a few hours later. This has meant that doing a bit of observing on work nights suddenly became a possibility. So when Yseult messaged me noting that the weather would be ideal for observing and it was a new moon, I was happy to observe on a Sunday night. Continue reading “Data: Stellar Quadrant Observations – 4/11/21”
Data: Stellar Quadrant Observations – 4/3/21
With the weather finally warming up, last night1 was was one of the nicest nights of observing one could really ask for. The daily high was in the low 70’s and the overnight lows were supposed to be in the mid-50’s. Humidity and winds were both low.
But with nicer weather happening and Easter today, everyone seemed to have plans already so I ended up heading out to Danville by myself. I’ve been wanting to capture some time lapse video of this so I took my GoPro out and tried the night lapse setting.
Continue reading “Data: Stellar Quadrant Observations – 4/3/21”
Almagest Book V: Components of Parallax – A First Approximation
So far in this chapter, we’ve explored how to use the table of parallax to calculate the parallax of the moon and sun by knowing its distance from the zenith. But this in and of itself isn’t particularly useful. For example, when we did a sample lunar parallax calculation, we determined in that situation, the moon was about $1;10º$ off from its true position. But $1;10º$ in which direction?
Thus, the next step will be to break that down into its components, determining how far off in both ecliptic latitude and longitude the parallax makes the moon appear. Ptolemy again gives steps, but no example, so we’ll continue the previous example we did for the moon, following Neugebauer2. Continue reading “Almagest Book V: Components of Parallax – A First Approximation”
Almagest Book V: Calculating Solar Parallax Along a Great Circle Through the Zenith
Having computed the lunar parallax,
the sun’s parallax for a similar situation [i.e., as measured along an altitude circle] is immediately determined, in a simple fashion (for solar eclipses) from the number in the second column corresponding to the size of the arc from the zenith [to the sun].
Well that sure sounds easy. Let’s look at a quick example. Continue reading “Almagest Book V: Calculating Solar Parallax Along a Great Circle Through the Zenith”
Almagest Book V: Calculating Lunar Parallax Along Great Circle Through Zenith
Now that we’ve completed the parallax table, we should discuss how to use it. As usual, Ptolemy will now walk us through the steps, but does not provide an explicit example so I’ll follow an example from Neugebauer3, to help illustrate the procedure.
As our goal, Ptolemy states that our goal is to find
the moon’s parallax at any given position, (first) with respect to the great circle drawn through the moon and zenith
Continue reading “Almagest Book V: Calculating Lunar Parallax Along Great Circle Through Zenith”
Data: Stellar Quadrant Observations – 3/6/2021
As usual, the weather in January and February of this year hasn’t cooperated. Nights were consistently cloudy during good moon phases or the temperatures well below freezing.
But as March has rolled around, temperatures have begun to warm, and the forecast called for a clear night with a good moon phase so Yseult and I headed out to Danville Conservation Area to do some observing. Continue reading “Data: Stellar Quadrant Observations – 3/6/2021”
Class Schedule
Almagest Book V: Parallax Table
In the previous chapter, we worked out the parallax for the sun and the moon at 4 different positions. Next, we determined how we might make some corrections for the moon if it were between the positions we described, breaking the corrections into ones for the epicycle and for the eccentre. From that work, Chapter $18$ presents the results in tabular format. Since this one is pretty wide, I’ve again made the decision to put it into a Google Sheet.
Update – 2/5/21: New Classes Are Coming
It’s been a few weeks since I’ve posted anything but it’s not because I haven’t been busy on astronomy. My recent activity just hasn’t been in the Almagest or observing. Rather, I’ve been working on some classes.
Almagest Book V: Lunar Distance Adjustments for Eccentre
So far in this chapter, we’ve reviewed how to calculate the lunar parallax for certain limits of the lunar position and looked at what’s necessary to estimate the effects for lunar positions away from those limits due to the epicycle. Now, we need to discuss the impact of the eccentre and how that we can estimate the effect on parallax due to it bringing the moon closer and further.
So let’s set up a generic diagram of our eccentric model, ignoring the epicycle and only concerning ourselves with the mean moon:
Continue reading “Almagest Book V: Lunar Distance Adjustments for Eccentre”