Book contents
- Frontmatter
- Contents
- Preface
- Using your personal computer for astronomy
- DEFAULT: default value input routnine & YESNO: ‘Y’ or ‘N’ input routine
- MINSEC: converts between decimal hours/degrees and minutes/seconds form
- JULDAY: calendar date to Julian day number since 1900 January 0.5
- CALDAY: Julian day number since 1900 January 0.5 to calendar date
- TIME: converts between local civil and sidereal times
- EQHOR: converts between equatorial and horizon coordinates
- HRANG: converts between right ascension and hour angle
- OBLIQ: calculates the value of the obliquity of the ecliptic
- NUTAT: finds corrections for nutation in longitude and obliquity
- EQECL: converts between equatorial and ecliptic coordinates
- EQGAL: converts between equatorial and galactic coordinates
- GENCON: converts between any of the coordinate systems
- PRCESS1: approximate precession of equatorial coordinates & PRCESS2: rigorous precession of equatorial coordinates
- PARALLX: converts between geocentric and apparent position
- REFRACT: calculates the effect of atmospheric refraction
- RISET: finds the circumstances of rising and setting
- ANOMALY: solves Kepler's equation for elliptical motion
- SUN: finds the ecliptic coordinates of the Sun
- SUNRS: finds the circumstances of sunrise and sunset
- PELMENT: returns the orbital elements of the major planets
- PLANS: finds the position of a planet
- MOON: finds the position and parallax of the Moon
- MOONRS: finds the circumstances of moonrise and moonset
- MOONNF: finds the times of new and full moon
- ECLIPSE: finds the circumstances of lunar and solar eclipses
- DISPLAY: displays an eclipse in graphical form
- ELOSC: finds positions from osculating elliptical elements
- RELEM: converts elliptic orbital elements from one epoch to another
- PCOMET: finds the position of a comet from parabolic elements
- PFIT: finds parabolic elements from observations & EFIT: finds elliptical elements from observations
- List of variables
- Bibliography
- Index
- PROGRAMS AVAILABLE ON DISK
NUTAT: finds corrections for nutation in longitude and obliquity
Published online by Cambridge University Press: 17 February 2010
- Frontmatter
- Contents
- Preface
- Using your personal computer for astronomy
- DEFAULT: default value input routnine & YESNO: ‘Y’ or ‘N’ input routine
- MINSEC: converts between decimal hours/degrees and minutes/seconds form
- JULDAY: calendar date to Julian day number since 1900 January 0.5
- CALDAY: Julian day number since 1900 January 0.5 to calendar date
- TIME: converts between local civil and sidereal times
- EQHOR: converts between equatorial and horizon coordinates
- HRANG: converts between right ascension and hour angle
- OBLIQ: calculates the value of the obliquity of the ecliptic
- NUTAT: finds corrections for nutation in longitude and obliquity
- EQECL: converts between equatorial and ecliptic coordinates
- EQGAL: converts between equatorial and galactic coordinates
- GENCON: converts between any of the coordinate systems
- PRCESS1: approximate precession of equatorial coordinates & PRCESS2: rigorous precession of equatorial coordinates
- PARALLX: converts between geocentric and apparent position
- REFRACT: calculates the effect of atmospheric refraction
- RISET: finds the circumstances of rising and setting
- ANOMALY: solves Kepler's equation for elliptical motion
- SUN: finds the ecliptic coordinates of the Sun
- SUNRS: finds the circumstances of sunrise and sunset
- PELMENT: returns the orbital elements of the major planets
- PLANS: finds the position of a planet
- MOON: finds the position and parallax of the Moon
- MOONRS: finds the circumstances of moonrise and moonset
- MOONNF: finds the times of new and full moon
- ECLIPSE: finds the circumstances of lunar and solar eclipses
- DISPLAY: displays an eclipse in graphical form
- ELOSC: finds positions from osculating elliptical elements
- RELEM: converts elliptic orbital elements from one epoch to another
- PCOMET: finds the position of a comet from parabolic elements
- PFIT: finds parabolic elements from observations & EFIT: finds elliptical elements from observations
- List of variables
- Bibliography
- Index
- PROGRAMS AVAILABLE ON DISK
Summary
The combined gravitational fields of the Sun and the Moon acting on the nonspherical Earth cause the direction of the Earth's rotation axis to gyrate slowly with a period of about 25 800 years. This effect, called precession, is calculated by routines PRCESS1 (2500), and PRCESS2 (2600). Superimposed on the regular motion there are also small additional periodic terms caused by the varying distances and relative directions of the Moon and Sun, which continuously alter the strength and direction of the gravitational field. This slight wobbling motion is called nutation, and it must be taken into account when accuracies of better than half an arcminute are required. The routine given here calculates the effects of nutation on the ecliptic longitude (DP) and on the obliquity of the ecliptic (DO). It has an intrinsic accuracy (reduced by lack of precision in your machine) of about 1 arcsecond.
The calculations are made by the routine for the date input as DY (days), MN (months), and YR (years). Execution is controlled by the flag FL(6). If this flag is set to 0 before calling NUTAT, execution of the routine continues normally. It is set to 1 at line 1865. Subsequent calls to NUTAT with FL(6) = 1 do not result in any new calculations, but control is returned immediately to the calling program.
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- Astronomy with your Personal Computer , pp. 55 - 58Publisher: Cambridge University PressPrint publication year: 1990