Having finished the quadrant this past weekend, I was finally able to take it out for it’s first light1. A special thanks to Her Excellency Slaine for helping me transport parts that wouldn’t fit in my car as well as Padrig for being my chief observer.
So how’d it go?
Before we went out, I printed out star charts from Stellarium for each star which I hoped would help us find them quickly. For the most part it did, but some fading daylight prevented some from being found. The bright moon wasn’t a huge help either since many of the target stars were fairly nearby.
Another problem was that the sites are rather difficult to use. They are sufficiently far apart that there’s no way to even come close to have both in focus. This means that you have to constantly switch your focus, but in the dark, trying to figure out where the forward one is means moving a bit, which gets you right back out of line. Padrig noticed that it ended up being easier to site down the side of the arm but I haven’t really tested that much.
The next challenge is that the quadrant needs to be aligned on the meridian. While this is quite easy to do, the central column rotates too freely. My dad and I discussed some plans on how to remedy this which we’ll likely build into the design in the near future.
Lastly, stars near the zenith are really hard to observe. The contortion necessary to get there is next to impossible.
Ultimately, we were able to observe nine stars in about 40 minutes. Not too bad. The Astronomy Society of Eastern Missouri was also at the location having an open to the public star party so there were a lot of passers by which also slowed us down. But I think with a line of trained observers we could easily double this number.
Here’s a copy of the log. All objects were viewed on the south meridian so with an azimuth = 180º.
| Object | Altitude | Sidereal Time |
| ε Oph | 46º | 16:20 |
| σ Sco | 25.2º | 16:23 |
| α Sco | 24.8º | 16:29 |
| β Her | 72.6º | 16:33 |
| τ Sco | 24.3º | 16:35 |
| ζ Oph | 40.6º | 16:37 |
| ζ Her | 81.7º | 16:41 |
| ε Sco | 17º | 16:50 |
| κ Oph | 60.7º | 16:57 |
These were then converted to RA-Dec which would allow me to compare the values from our measurements with published values. However, since each star was on the meridian, that means that each of their hour angles would be zero. In turn, that means that their RA would equal the sidereal time. Since I only concerned myself with sidereal time to the minute, as long as the reading was taken in the same minute, the RA always comes out with no deviation. Thus, it’s not much of a meaningful measurement.
Rather, we get a better idea of the instrument’s capabilities from the Declination.
When averaging all the residuals, the average came out to be 0.15º or 9 arcminutes. This is a very nice start.
However, there was quite a bit of scatter. For example, our declination for τ Sco was -1.22º and ζ Her was +1.18º. These two pretty much canceled themselves out for the average, but notably increase the standard deviation to 0.65º which is 39 arcminutes.
Ultimately, I think the instrument is a pretty big success. Working on better techniques for sighting, not being rushed and interrupted while observing, and some minor improvements to the quadrant will all probably help beat those errors down, as will numerous observations of the same stars.