Introduction

Main Input Screen

Body Selector Window

Calendar and Print Options

Sunrise, Sunset, and LAN

Moonrise and Moonset

Accuracy and References

Arc to Time Table

StarPilot Programs

Almanac Accuracy and References

The accuracy level of SPA matches or surpasses that of the Nautical Almanac. The data for sun and stars are valid for essentially any year, but prior to 1582 one must be sure that Julian dates are being used. The moon data contain uncertainties of up to several minutes prior to 1620, as some critical input are not known prior to then. Likewise moon data must be updated for accurate data after 2011, but this should become available well before then.

Specific accuracy specifications are itemized below.

Body

Accuracy

Sun

2" [ A ]

Moon

10" [ B ]

Mer, Ven, Mar

< 10" [ C ]

Jup, Sat

< 10" [ D ]

173 Stars

2" [ E ]

A . Planetary programs are used to analytically compute positions. Corrections for nutation and aberration are also included. (Ref: 10, 9)

B . ELP-2000/82 Lunar theory is used in addition to corrections for nutation and aberration. (Ref: 7, 9)

C . As in C with corrections for planetary aberration. (Ref: 10, 9)

D. Planetary tables are used for the period 1960-2100 AD. For years not in the stated period VSOP 87 planetary theory is used. Corrections for nutation and aberration are also included, with additional corrections for planetary aberration. (Ref: 10, 7, 9)

E . Star positions for the ecliptic of 1975 are transformed to the positions relative to the ecliptic of date, with additional corrections for nutation and aberration. (Ref: 3, 9)

Bibliography

  1. Nautical Almanac, US Naval Observatory, Washington DC, 1978,1981,1988,1991,1996.
  2. Almanac for Computers, US Naval Observatory, Washington DC, 1985.
  3. Astronomical Almanac, US Naval Observatory, Washington DC, 1975.
  4. Astronavigation Now it's Child's Play, Mike Harris, Practical Boat Owner, No 258, pg. 58, 1988.
  5. Which Star?, John Jeffrey, Practical Boat Owner, No 273, pg. 145, 1989.
  6. Practical Ephemeris Calculations, Oliver Montenbruck, Springer-Verlag Heidelberg, 1989.
  7. Astronomy on the Personal Computer, Oliver Montenbruck, Springer-Verlag Heidelberg, 1989.
  8. Astronomical Algorithms, Jean Meeus, Willman-Bell, Inc., 1991.
  9. Astronomical Formulae for Calculators, Willman-Bell, Inc., 1988.
  10. Practical Astronomy with Your Calculator, Peter Duffett-Smith, Cambridge University Press, 1988.
  11. Planetary Programs and Tables from -4000 to +2800, Pierre Bretagnon and Jean-Louis Simon, Willman-Bell, Inc., 1986.
  12. Celestial Navigation in the Computer Age, Alton B. Moody, Van Nostrand Reinhold Company, 1982.
  13. Navigation Afloat, Alton B. Moody, Van Nostrand Reinhold Company, 1980.
  14. Piloting/Navigation with the Pocket Calculator, Jack Buchanek and Ed Bergin, Tab Books, 1976.
  15. Coastwise Navigation, Stafford Campbell, Ziff-Davis Publishing Company, 1979.
  16. On the Overdetermined Celestial Fix, Thomas R. Metcalf and Frederic T. Metcalf, Navigation: Journal of the Institute of Navigation, Vol. 38, No 1, 1991.
  17. Advancing Celestial Circles of Position, Thomas R. Metcalf, Navigation: Journal of the Institute of Navigation, Vol. 38, No 3 1991.
  18. Manual for the Tamaya NC-77 Digital Navigation Computer, Tamaya Technics, Inc., Tokyo, Japan, 1978.