Last night was the much hyped Great Conjunction of Jupiter and Saturn. I was asked if this had any meaning for my project. It really doesn’t have any special astronomical meaning, but it was fun to look at through a telescope. However, I decided that this would be an interesting stress test for the quadrant. After all, Jupiter and Saturn were only $6$ minutes of arc apart. This is a single division on the quadrant’s scale. So could I actually tell them apart?
To find out, I took the quadrant out to Broemmelsiek. Knowing that it was going to be crowded, I decided to go in full garb, and indeed, it prompted several people to stop by and ask questions. So if you’re one of the people I handed a card out to, welcome!
Unfortunately, I forgot to bring the azimuth ring with me, so I’ll have to look up the azimuth in Stellarium which is cheating, but the best I can do since by the time I got home to grab it, the event would have been nearly over, even if I didn’t come back out.
However, this does mean that I essentially eliminated the azimuth as a variable so any error must be the result of errors in the altitude or the sidereal time. With sidereal time, I take this number off an app on my phone so it’s highly reliable. However, because I don’t suspect that period clocks could be accurate to the second, I round down to the nearest minute since it takes me a bit to clamp the quadrant arm and climb down the ladder. However, even $30$ seconds here can be a notable difference in the right ascension: about $0.15º$. So really, I think this potential error entirely swamps the potential for determining if the quadrant can read down to $0.10º$ ($6$ arcminutes) if it could.
That being said, I was able to take $4$ measurements of both Jupiter and Saturn before they were too low to point the quadrant at and the overall error for both was right about $0.33º$ which is clearly larger than any potential error due to the sidereal time. So clearly, from a few measurements, the quadrant is not that precise. At least, from a few measurements. As we’ve seen from the larger averages, it gets closer.
I think there’s definitely some improvements to be made with the sights which would help, so that’s going to be on my project list for the coming year!
If you’re looking for some historical information on the great conjunction, the Renaissance Mathematics blog has a great post.