NavList:

Hello Frank,

Thank you very much for your valuable comments.

Here goes some additional information:

• You pinpointed the exact location where I was taking the sights. From that position I could see around 180 degrees of river view and I was able to use the river as a natural horizon for both the sun and the month.
• The fact that it is next to the Buenos Aires’ regional airport is just coincidence. That place is also around 15 minutes’ drive from my apartment in Buenos Aires.
• Both average lunar and sun altitudes are the real altitudes taken with the sextant. When available, I always try to take the actual altitudes (an average them), because I after doing the lunars calculation, I use those same sights and times to do a regular sight reduction (LOP or cosine rule method) to check the position error (which in this case it was 1.2 nm).
• In case I can not take the actual altitude against the horizon of one of the celestial bodies, I always have the A12 bubble sextant handy.
• As you explained in the course, and I was able to confirm in the last lunars, a small variation in the sextant index error makes a significant difference in the cleared lunar distance, so I use the regular LOP sight reduction to confirm that the index error taken when calibrating the sextant makes sense. In my experience in doing regular sight reductions with the Mark II sextant the position error varies between 0.8 and 1.5 nm.
• The average times are the correct ones, but the Mark II has a very small horizon mirror, so it is always a kind of difficult “to kiss” the sun and the moon, so it took me around 5 minutes to take four lunar distances.
• As you said, the moon’s bight limb was clear enough to take lunar distances, but the altitude of the moon respect to the horizon was not a good one because the lower limb was too dark. That might have introduced a little error in the position calculation with the LOP method.
• I always use your app to see the lunar results and then I compare it with the spreadsheet I developed. This spreadsheet calculates both the cleared lunar distance and the true lunar distance, and that is another reason that I need to take the precise moon and sun altitudes with the sextant (and the corresponding times). In general, both results are very close to the ones on your app.
• With both your app and my spreadsheet, I always play by changing some inputs that might be estimated such as height of eye, temperature, and pressure. Index error is not estimated, but it is also interesting to see the a decimal change makes a significant diference in the cleared lunar distance.

Learnings from this experience:

• Sextant calibration and using the correct index error is critical in the lunar’s precision.
• Always run a regular sight reduction using the moon and the second body (if using real altitudes imputs) to make sure the sextant is working properly.
• The Mark II sextant reading marks are 0.5 separated, so I had to estimate what decimal to use.
• The Mark II telescope is not very powerful and that combined with the small horizon mirror makes it not the most appropriate one for lunars.   
• Although I also own a 1953 C. Plath and a1967 Tamaya sextants that are better for lunars, the Mark II is the only one that fits my carry-on luggage. I am not putting a sextant in the checked luggage.  

Again, thank you very much for taking the time to read and make comments on these lunar’s experiences.

Martin (from Buenos Aires, Argentina)