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 26,000-year precession of the Earth's axis of rotation. It is mainly caused by the gravitational effect of the 18.6-year rotation period of the Moon's orbit. The main component of this 18.6-year oscillation is illustrated clearly in the graphs below.

19-Year 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 X-axis and used as arguments on the Y-axis functions.


19-Year Nutation Cycles                                                      

19-Year 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 X-axis and used as arguments on the Y-axis functions

 


19-Year Obliquity vs Longitude Cycle                

This is the line the
Earth's pole would
"draw" in space due
to nutation alone.

Close-up of a Knot on Chart

The close-up below illustrates how complex this motion can be in the region of a knot in the above graph. To see a day-by-day 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

 


Close-up of a Nutation Knot

Click Icon to View
Animation

(Caution! If viewing on the web, clicking the hand will start downloading  a 620KB AVI movie file.)

Astro Utilities Electronic Book Copyright 1999 Pietro Carboni. All rights reserved.

 

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