astrolibR (version 0.1)

nutate: Calculate the nutation in longitude and obliquity for a given Julian date

Description

Calculate the nutation in longitude and obliquity for a given Julian date

Usage

nutate(jd)

Arguments

jd

Julian ephemeris date, scalar or vector

Value

nut_long

nutation in longitude, same number of elements as jd

nut_obliq

nutation in latitude, same number of elements as jd

Details

This function uses the formula in Meuss (1998, Chpt. 22) which is based on the 1980 IAU Theory of Nutation and includes all terms larger than 0.0003".

References

Meeus, J., 1998, ``Astronomical Algorithms'', 2nd ed.

See Also

cirrange polyidl

Examples

# Find the nutation in longitude and obliquity 1987 on Apr 10 at Oh.
# Result: nut_long = -3.788    nut_obliq = 9.443
# This is example 22.a from Meeus

jul = jdcnv(1987,4,10,0)
nutate(jul)
       
# Plot the large-scale variation of the nutation in longitude 
# during the 20th century. This plot will reveal the dominant 18.6 year
# period, but a finer grid is needed to display the shorter periods in 
# the nutation.


yr = 1900 + seq(0,100)    # establish sequence of years      
jul = jdcnv(yr,1,1,0)          # find Julian date of first day of year
out = nutate(jul)               # compute nutation
plot(yr, out$nut_long, lty=1, lwd=2, xlab='Year', ylab='Nutation longitude (degrees)')