Astrolabes were designed to be hand held and as a result had to be fairly small. The small size limited their precision. An astronomical quadrant or sector could be made much larger. Tyco Brahe was said to have had one that was said to have been 2 meters tall that supposedly allowed measurements in the sub-arcsecond range.
Some quadrants were fixed mounted on walls and as such that they were usually aligned north-south. This enabled them to measure objects only as they transited the meridian. Others were able to rotate, and it was possible to read the azimuth (heading) too. The second type had to have the azimuth scale aligned to the north pole prior to use. The alignment was possibly done by the same methods you used to find north above.
Construct an astronomical quadrant. It doesn’t have to be as large as the one in the picture but try to make it at least one foot on a side so it is significantly larger than your astrolabe. It should be noted that an astrolabe is self leveling while a quadrant is not. Make sure to level your quadrant prior to using it.
Here are the instructions of the quadrant I plan to build.
Here are pictures of the construction of my quadrant.
Practice using your quadrant by measuring:
1. the height of Polaris
2. the elevation of a few bright stars as they cross the meridian at night (transit)
3. the altitude and azimuth of the moon and planets.Record the dates and times along with your observations.
I was planning on going out Sunday Feb 4, 2024 to capture the four Orion navigation stars transiting. The night before, we got 6 inches of wet snow.
I scooped out the area of snow, south of the streetlight so I could setup there tonight. I need to be south of the streetlight, which is in front of the white truck in the picture above, so the light doesn't illuminate the end of my site tube and I can see the second magnitude stars of Orion tonight.
By the time I am ready to observe the transiting stars about 8 pm, this area will be dry.
Items 1 & 2:
Compare the use and results from your work with an astrolabe and quadrant.
Do you have a preference?
I found using the Astrolabe easier than setting up the quadrant, aligning it and then making readings of the azimuth and altitude scales in the dark. As can be seen in the table above, the Astrolabe was quite accurate when compared to my quadrant altitude readings.
Does one seem easier to use?
I liked using the Astrolabe. It is very accurate and simple to use. I did need a red headlamp to light up the two pointers in the dark. But that was easy to do and in a few seconds, I had the pointers aligned on the stars.
Does one give better data?
Both the Astrolabe and Quadrant gave very similar readings.
It is interesting to know that Kepler used data from one of Brahe’s quadrants to get the data to verify his three laws of planetary motion.
I built my quadrant with a 12" long piece of 1/2" PVC tubing. I found that there was some variation in where the star was centered in the tube, depending where my eye was positioned at the bottom end of the tube. I found that with care, I could center the stars/planets with consistent accuracy.
If I were to do this Program again, I would increase the size of my quadrant significantly. I would also use a board with a V-channel in it so that aligning the quadrant on a target would remove the need to have your eye in a certain position. I would sight up the groove and my eye would always be in the correct position.
Items 3:
