Lunars are easy when you have a Nautical Almanac and the pre-computed lunar distance tables! The lunar distance tables have not been published in the Nautical Almanac since 1906 but ezLunars has brought them back.
The lunar distances of up to 6 navigational bodies are provided at 3-hour intervals, along with the proportional logarithm value needed to interpolate the distance to the universal time at the time of your observation. A proportional logarithm table, moon augmented semidiameter, and second differences table are also provided. All tables can be easily printed to a wireless printer or saved to a PDF file for use outside the app.
ezLunars includes functions to guide you through the process of making the observations and using the tables to compute universal time, guiding you through the process and demonstrating how to use the tables.
The lunar distance tables show daily lunar distances of the best 6 objects along the ecliptic to use. The distances are shown at 3-hour intervals and include a proportional logarithm value necessary to interpolate to the correct distance at the time of the observation. This is the same data published in the Nautical Almanac until 1906.
The proportional logarithm table is included to convert between the logarithm value and time. The "Second Difference Correction" table from the 1906 Nautical Almanac is also included. This correction adds additional accuracy when objects very close to the moon have a higher than normal rate of distance change.
The Bowditch "Common Logarithms of Trigonometric Functions" tables are useful for clearing the lunar distance using simple addition and subtraction when doing lunars manually.
All tables support highlighting by dragging in the table when used manually from the app. When the app functions to perform lunars are used, table values used can be highlighted in the table to demonstrate table usage. Nautical Almanac values needed to correct your observations and determine Sun and Moon semi-diameters can also be highlighted on the correct almanac page.
All lunar tables can be printed via AirPrint or exported to a PDF file for manual use outside the app.
App functions walk you through the steps to select the object to use, make and correct the object altitudes and lunar distance measurements with your sextant, and finally clear the lunar distance and determine universal time.
A starmap function aids in determining the best navigational body to use and the best times to make your observations. The app functions support using any navigational body along the ecliptic (shown in red on the starmap) for your lunar.
All functions show the table values used in the function displayed on a button. Press the button to highlight that value in the table that it is found.
Each function page has an accompanying user guide page that explains each field and control.
In-app users guide pages explain the controls and values on each function page. In addition, a users guide page, "Your First Lunar!", walks you through the steps to use the app functions to make your observations and clear the lunar distance to determine universal time.
The paper "About Lunars" by George Huxtable is included in the app. It is a very easy to read and understand explanation of lunars and how to perform them. It discusses both the Young and Borda methods for clearing the lunar distance. These are 2 equivalent and mathematical correct methods that are both supported by ezLunars.
The include paper "Longitude Mathematics" by Wong Le Nah is an excellent discussion of the history, and shows the full detail of the math involved. Very Interesting!