It’s getting to that time of year where the weather becomes extremely unpredictable. Warm enough to have the windows open one day and an ice storm the next.
Despite it being cold this past Friday night, the sky was at least clear with no wind so Yseult and I went out to do some observing.
We did have a bit of a hiccup due to some items missing from the bag of loose parts. Specifically, we have a set of small wood blocks that go underneath the base for the leveling screws to dig into so they don’t sink into soft ground. But these have gone missing. As an emergency replacement, we pulled all of the floor mats out of the car and were able to use those although leveling was still quite tricky.
But once we did get things sorted out, we were able to get started mostly doing stars in Eridanus, Cetus, and Taurus.
This time we tried out using the list of stars I’d put together when I originally envisioned this project to help ensure that we didn’t skip stars simply because they were faint. I’d updated the list prior to going out to ensure that we included all stars in these constellations down to magnitude $4.5$. However, it appears we’d done a reasonably good job previously as, out of $28$ stars we observed, only $6$ of them were new to the catalog.
When observing, Yseult and I tend to both take observations of the same star. There’s two reasons for this. The first is that, once we select a target, getting a second reading is generally pretty quick and easy. This means we build up the number of observations more quickly, thus increasing the statistical certainty on the object.
Second, it’s fun to be somewhat competitive and see who the better observer is. In general, we’re both pretty close.
But this time we noticed that, while our altitudes were generally within $\frac{1}{2}º$, our azimuths were typically $1.5-2º$ apart with mine being higher. Ultimately, theirs ended up being significantly more accurate which means that something went wrong on my end.
Knowing this, it’s pretty clear what the issue is. First, when we align the instrument on Polaris, Yseult was the one that sighted it while I aligned the azimuth ring.
When observing, we have slightly different techniques for doing so. For my part, I tend to first align the altitude. Then, I can hold the rotating part of the quadrant against the “wings” we added behind it to hold the altitude steady while I rotate it left and right to align the azimuth. However, there’s a bit of play in the quadrant which means that, when I pin it against the wings, it points the sights slightly to the left. Therefore, I have to rotate the quadrant further to the right to make up for this.
When observing by myself, this isn’t an issue since this I do the same thing when aligning, making the offset caused constant for all observations. But since we aligned based on Yseult’s techniques, which allow the quadrant to hang freely, this introduced a bias in my observations. One which was far more significant than I anticipated.
As a result, I threw out nearly all of the observations I made and in the future, I don’t think we’ll continue taking turns observing the same object since there’s such an issue.
Ultimately, the data weren’t nearly as good as they’ve been in the past, with the right ascension averaging low by $0.27º$ with a standard deviation of $0.43º$. The declination also tended high by $0.43º$ with a standard deviation of $0.32º$.