Identify the source used to compute times of sunrise and sunset.  

Compute times of sunrise and sunset using the Sunrise and Sunset tables.

Identify the procedures used to convert Local Mean Time to Local Standard Time and Universal Time Coordinated.

Define twilight, and identify the tables and procedures used in twilight computations.

Identify the table, graphs, and procedures used to compute sunrise, sunset, and twilight for locations north of 72 N.

The positional relationship of the Sun and Earth is critical to the climatic controls influencing Earths environment. Because of Earths elliptical orbit around the Sun, the amount of sunlight varies with latitude. As we have already discussed in AG2 - Volume 1, some regions of Earth spend 6 months of the year in darkness, while other regions get more sunlight than darkness and vice versa.  

The Earth-Sun relationship can also play an important part in naval operations. The length of daylight versus darkness, or the time of sunrise and sunset can be critical to many peacetime, as well as wartime, operations.

Aerographers Mates are usually tasked with computing the times of sunrise and sunset for their own stations. Usually, the times are computed months in advance, and the daily information is published in the plan of the day and/or the daily weather bulletin.

Table 6-7-1 is a sample of the Sunrise and Sunset tables as taken from the 1989 edition of Air Almanac. The top table is for sunrise computations, while the lower table is used to compute sunset.

The tables are formulated in the same manner. Latitudes between 72N and 60S are listed vertically on the left in various increments. Two-degree increments are used between 72N and 50N; five-degree increments are used between 50N and 30N, etc. The months and dates are listed horizontally across the top of each table in 3-day increments.

The Sunlight and Twilight table, which I will discuss further later, is used to compute sunrise and sunset for latitudes north of 72N. Air or below the horizon, symbols are used in place of the hours and minutes. The symbol is printed for those latitudes and dates when the Sun is continuously above the horizon, and is used when the Sun is continuously below the horizon. The times are in Local Mean Time (LMT) and must be converted to Local Standard Time (LST) or Universal Time Coordinated (UTC). I will cover the time conversion later in this lesson.

Learning Objective: Compute times of sunrise and sunset.

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