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Floppy Almanac


The Floppy Almanac was the first accurate astronomical ephemeris program for personal computers, and the first computer application produced by the U.S. Naval Observatory for unlimited distribution. The USNO Nautical Almanac Office developed the Floppy Almanac in the mid-1980s to run on the earliest Intel-based PCs. The program did not require a hard drive; it could execute on a computer with only 256K of memory (some calculations were, however, a bit sluggish!). The executable was self-contained; it required no external files. The entire product fit on one 360K floppy diskette. Just like its paper counterpart, the Astronomical Almanac, the Nautical Almanac Office issued a separate edition for each calendar year. Distribution of the first two Floppy Almanac editions, for the years 1986 and 1987, started in the fall of 1986. The Floppy Almanac rapidly became popular.

The original Floppy Almanac featured source code entirely written in ANSI standard Fortran 77 and a user interface designed for a "dumb" terminal. Therefore, the Floppy Almanac was easily portable to many kinds of computers, including IBM 370 mainframe systems and DEC MicroVAX systems.

By the late 1980s, the Nautical Almanac Office created a friendlier user interface for the Floppy Almanac, but it was of necessity PC-specific. At the time, portability seemed less important than ease of use for the large number of PC users. The Nautical Almanac Office also developed a version of the Floppy Almanac that provided data for extended periods of time—the Interactive Computer Ephemeris (ICE).

In 1993, Version 1.0 of MICA, the Multiyear Interactive Computer Almanac, superceded the Floppy Almanac. The initial version of MICA, for both DOS-based PCs and Macintosh systems, had a much more modern user interface than did the Floppy Almanac, provided a wider range of tabulations, and supplied astronomical data for ten years. The Nautical Almanac Office continues to develop and support MICA.

The Nautical Almanac Office no longer develops or supports the Floppy Almanac.