Use your astrolabe, quadrant and cross-staff to measure (pick the tool which you think is best for the task):
1. pick a star and measure
2. how far it moves in an hour, how far the moon moves versus a star you choose in an hour
3. angular diameter of the moon, (is your instrument precise enough to do this?)
4. the two diagonals of the Great Square, (is it really a square?)
5. the azimuth of the rising full moon for three months in succession
6. the altitude of the full moon one hour after it rises for three months in succession
7. the angle(s) between the following:
- Betelgeuse and Rigel
- Castor and Pollex
- The three stars in the Summer Triangle
- two planets at conjunction
For the above four measurements, I used my Jacob's Staff. I found my results surprisingly close to the actual values.
While making these measurements, I was positive I had the stars just at the edge of each marker before recording the measurements. I noticed the farther the distance is between the markers, the less reliable this tool was in making an accurate measurement of the separation of the stars. That can be seen in the measurements between Betelgeuse and Rigel, Deneb and Altair and Vega and Altair.
I used my closed fist as 5 degrees and the separation between the two planets was about two-thirds of the distance across my knuckles.
When I started this program, Venus (upper) and Jupiter (lower) were in conjunction. This picture was taken minutes after making the Venus and Jupiter reading with my Jacob's Staff.
- Venus and the Sun monthly for ½ a cycle from when it first appears in the evening (or morning) sky until it disappears about ten months later. Plan your observation for just after the Sun sets (or before it rises in the morning). Don’t look directly at the Sun. Wait until it just dips below the horizon.
Many amateur astronomers use their fists (10 degrees), three fingers (5 degrees), and a pinky finger (1 degree) to estimated angular distances in the sky. Do you find that these earlier instruments give equal or better measures?
