Nautical Astronomical Almanac, 2025-2026

DOI: 10.32876/NavalAlmanac.2025-2026

Preface

Institute of Applied Astronomy of the Russian Academy of Sciences (IAA RAS) submits the next issue of "The Nautical Astronomical Almanac for the years 2025-2026" biennial (NAA-2).

NAA-2 is based on the "[The Nautical Astronomical Yearbook] (../../nautical-yearbook)" (NAY), also prepared by the IAA RAS. NAA-2 provides an easy access to a useful navigation publication which is constantly present aboard a ship and has a longer period of validity as compared to standard navigation manuals. The almanac does not require any other publications for observation processing
and gives the same accuracy of basic astronomical parameters as NAY does. NAA-2 contains detailed algorithms of solving the navigational tasks, such as determination of compass correction and finding a ship's position by means of the Sun's and stars's observations. It also contains instructions for the use of the marine sextant, the celestial globe, star charts and fixing position plotter for the determination of a ship's location.

The structure of "The Nautical Astronomical Almanac for the years 2025-2026" has not undergone essential changes in comparison with the previous issue of NAA-2. The theoretical basis of ephemerides is the EPM2011m theory of movement of the Solar system bodies created in IAA RAS. In accordance with the resolutions of XXIV and XXV General Assemblies of International Astronomical Union positions of stars are published in the system of FK6 and HIPPARCOS catalogues referred to International Celestial Reference System (ICRS) based on the observations of extragalactic radio-sources. Thus, consistency is achieved between the data published in NAA-2 and Russian "Astronomical Yearbook" which is the basis for planning and carrying out astronomical and geodetic programs. The Explanation and part of auxiliary tables are given in both Russian and English versions. The detailed description of theoretical basis of modern astronomical ephemerides, as well as algorithms for their calculation may be found in "[The Extended Explanation to the Astronomical Yearbook] (../../transactions / t10)" published in "Transactions of IAA RAS", 2004, v. 10 (in Russian).

The basic contents of NAA-2 are daily tables. They include ephemerides of hour angles of the first point of Aries, the Sun and the Moon, declinations of the Sun and the Moon for each hour, and also hour angles and declinations of planets (Venus, Mars, Jupiter and Saturn) with a 5^h^ step and to within 0.1'. Besides, the times of sunrises and sunsets are given for 68 values of latitude. Azimuths of the upper limb of the Sun for risings and the opportunity time of the beginning of morning and evening observations of stars are also included.

The apparent places of 160 navigational stars are given for the beginning of each month in a special table, with the apparent places of 77 brightest stars being available in daily tables for every three days of a year (accuracy 0.1'). The tables of azimuths of Polaris (North Star) are given with accuracy 0.1°.

NAA-2 contains brief data on solar and lunar eclipses, configurations of planets, phases of the Moon and dates of the beginning of astronomical seasons. It also contains tables for the calculation of time of moonrises and moonsets to within 0.1^h^ according to the time of lunar culmination and latitude of the observer. There are some auxiliary tables for interpolation and calculation of altitude and azimuth in NAA-2.

Calculations of ephemerides in NAA-2 for 2025-2026 have been executed by the following researchers of the Laboratory of Astronomical Yearbooks of IAA RAS:

• hour angles of the first point of Aries, coordinates of the Sun, Moon and planets, the moments of culminations, parallaxes, visible semi-diameters and phases of the Moon, configurations of planets, the beginnings of seasons - N.B. Zhelesnov;

• conditions of visibility of planets, apparent places of stars, tables of azimuths of Polaris - G.A. Kosmodamianskiy;

• the time of sunrises and sunsets, azimuths of the upper limb of the Sun for the time of sunrise, the time of the beginning of morning and evening observations, tables of corrections to the time of the culmination of the Moon for calculation of moonrises and moonsets, eclipses of the Sun and the Moon - M.V. Lukashova.

The Explanation for NAA-2 (2025-2026) is revised by G.A. Kosmodamianskiy, M. V. Lukashova. Examples for NAA-2 are calculated by G.A. Kosmodamianskiy. The data control over various sections of NAA-2 is made by G.A. Kosmodamianskiy, M.V. Lukashova, I.A. Lebedeva, and A.M. Yurchenko.

The original of the Explanation for NAA-2 is prepared by M.V. Lukashova and G.A. Kosmodamianskiy. Presentation of the fixing position plotter, star charts and diagrams of visibility of planets in PS-format is made by G.A. Kosmodamianskiy. Editing version of the tables is made by D.A. Ryzhkova by means of the "PUBLISHER", an imposition system for tabulated editions developed in IAA RAS.

The work on editing the Almanac has been headed by editor-in-chief G.A. Kosmodamianskiy, with active participation of all the researchers of the Laboratory.

With the intention to solve basic astronavigation tasks, described in NAA-2, IAA RAS has developed the first version of a remote access system "The Navigator". The solving of tasks is carried out in accordance with the accepted in this edition accuracy (0.1') with output of a solution algorithm in the form of examples published in it (M.V. Lukashova, V.I. Skripnichenko, G.A. Kosmodamianskiy). The system "The Navigator" is available from the Internet\break https://iaaras.ru/dept/yearbooks/shturman/.

In conformity with the STCW-95 Code provisions, every navigator should be able to use classic methods of Nautical Astronomy. Therefore, they will undoubtedly appreciate the new "Nautical Astronomical Almanac" presented.

"The Nautical Astronomical Almanac" has been approved by the Department of Navigation Safety of the State Marine Fleet Service (ROSMORFLOT) of the Ministry of Transport of the Russian Federation, and it is recommended for navigators in the Russian Federation.

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