Earth's Nutation Visualized
[NOTE: The three diagrams on this sheet can take minutes each to
draw on slower (200 MHz) machines. If this is the case for you, just hit
the escape key and OK. This will allow you to scroll down and examine the
sheet without live graphics.] (If viewing the
web version ignore  graphics are static)
Nutation is a small cyclical motion superimposed upon the steady
26,000year precession of the Earth's axis of rotation. It is mainly
caused by the gravitational effect of the 18.6year rotation period of the
Moon's orbit. The main component of this 18.6year oscillation is
illustrated clearly in the graphs below.
19Year Nutation Cycles Chart
Nutation graphed here is
divided into components along (longitude) and perpendicular (obliquity) to
the ecliptic  not the Earth's equator. The chart is setup to display two
cycles of this phenomena.
Chart Input Parameters 

Enter Start Date 
Enter Day Increment and Year Span of chart 


Calculate Nutation Function
Arguments
The range of day numbers are
used to generate dates in Julian century format. These are charted along
the Xaxis and used as arguments on the Yaxis functions.
19Year Nutation
Cycles
19Year Obliquity
vs Longitude Cycle Chart
These next two graphs
illustrate the motion of the Earth's pole in the ecliptic reference frame
due to the combined nutation in obliquity and longitude. The effect of
graphing motion in obliquity versus longitude will illustrate the path of
the planet's pole due to nutation.
Chart Input Parameters 
Enter Year Span 
Enter Day Increment 


Calculate Nutation Function
Arguments
The range of day numbers are
used to generate dates in Julian century format. These are charted along
the Xaxis and used as arguments on the Yaxis functions
19Year Obliquity vs Longitude
Cycle

This is the line the
Earth's pole would
"draw" in space due
to nutation alone. 
Closeup of a Knot on
Chart
The closeup below illustrates
how complex this motion can be in the region of a knot in the above
graph. To see a daybyday animation of the motion click the Movie Icon
below the graph.
Chart Input Parameters 
Start and End Year 
Increment Step in Days 


Calculate Nutation Function Arguments 
Calculation of Julian Century per Days Incremented
in Selected Range 



Animation Frame Calculations 



Closeup of a Nutation Knot
Astro
Utilities Electronic Book Copyright © 1999
Pietro Carboni. All rights reserved.
EBook
Navigation User Constants
Usage Notes Astro Terms
Support 