Forum Replies Created
September 11, 2021 at 12:01 pm #10505
I have been sailing for over 20 years now, and flying for about 10 years, so I always had to use charts to create navigation and flight plans. Although you can create a either a marine or flight plan with the computer, during the instruction and license test you have to demonstrate you can do it manually.
Celestial navigation came naturally after that, in theory as a back up plan (in particular in a sailboat), but more for fun and also to give my amateur astronomy hobby a practical application.September 11, 2021 at 11:50 am #10504
Hi Joseph, there are a couple of software to do sight reductions that have the nautical almanac until 2050 or even 2100. If you want the current copies of both the nautical and air almanacs, go to http://www.thenauticalalmanac.com and download them from there.September 8, 2021 at 8:51 pm #10500
Thanks JDavHouston for your comments.
I tried a couple times to do “lunars”, but the tables available with the angles between the moon and the stars and planets are not very clear to me. If you can recommend any publication to learn more about the technique, I would appreciate it.
As you probably know, the nautical almanacs stop publishing the lunar tables back in the 1910’s
On the other hand, with the bubble octant, I have tried a couple of time the meridian passage sight of the moon, using the same technique you would use with the sun to calculate latitude and longitude. I did it both when the moon crosses the local meridian during the day and also during the night, and worked pretty well.
In both cases, the sights were taken at from my home’s backyard in Miami.
The next challenge is to try the meridian passage sights of the planets and some of the navigational stars.
By the way, I also have a commercial, instrument single and muti engine pilot license. I only fly for fun around Florida and I have around 500 hours of experience.September 8, 2021 at 3:40 pm #10497
Bubble octants can be used anytime of the day you cannot see the horizon for meteorological reasons, or anytime at night that is convenient for you based on the starts, planets and moon available.
This is the great advantage of the bubble octants over regular marine sextants. However, if you are on a ship in the middle of mid to heavy weather (day or night) when the ships rolls and pitch all over, it would be quite a challenge to take a sight with the bubble moving all over the display. The same would apply for a plane under heavy turbulence. In relative calm seas or on the ground, that problem is gone and you can use the octant anytime, anywhere in the world.
The nautical almanac and sight reduction tables are 24 / 365, so you can use them anytime, with the respective interpolation when need it. The main difference between the nautical and the aeronautical almanacs, is that the nautical almanac gives the data by hour (from zero to 24 hs) and the aeronautical gives the every ten minutes, every hour, so it is easier to interpolate when need it.
Regarding the Mark V octant, it was designed in the 1930’s and weights around 4.5 pounds. It is a little heavy, but no problem to handle with both hands. This model, also has a natural horizon option, so you can also use it as a regular marine sextant.
By the way, in case you do not know why the bubble ones are called octants and the marine versions sextants, here goes the explanation:
it is because in the case of octants, the altitude range you can measure goes from 0 to 90 degrees but the range of the scale only moves 45 degrees (because of the double reflection principle). 360 degrees / 45 degrees range = 8 (octant).
The marine sextants can measure altitudes with a range from o to 120 degrees, but the range of the scale only moves 60 degrees (same principle of reflection): 360 degrees / 60 degrees range = 6 (sextant).
If you measure any celestial body with an altitude higher than 90 degrees (only with a sextant), it would mean that body is actually “behind you back” respect to the natural horizon you are using as a reference. Why you would do that ? In case the natural horizon on the same side of the body your are taking a sight of is not visible for any reason (weather or even the coast), you can use the opposite side horizon as a reference, as long as the body is at least with an altitude of 60 degrees or higher to respect to the body same side horizon.
With a bubble octant, you do not need to take any angle higher than 90 degrees, because you always have an artificial horizon as a zero reference for altitude. It the altitude of the body is higher than 90 degrees, just turn around towards the azimuth where the body is located. That is another great advantage of the octants.
I hope my explanations are clear enough, and please let me know if you have any questions.
Best regards, MartinSeptember 6, 2021 at 11:02 pm #10495
In my case, I have been using a regular marine sextant for a couple of years and a few months ago I got an A12 and recently a Mark V both with artificial horizons. (the Mark V have both artificial and natural horizons)
I have tested both on land taking sights of the sun, moon, planets and starts in different location in Florida, Spain and Argentina. The A12 worked fine with errors between 3 and 8 miles, and the Mark V worked even better with errors between 2 and 6 miles compared to the real GPS positions.
Considering that both the A12 and the Mark V were built in the 1940’s, I would say that the results were quite satisfactory.
The great thing about a sextant with artificial horizon, comes at night because you can take sights of the moon, planets and stars (and a combination of them for a more accurate fix), any time at night and not necessarily during nautical twilight.