Earth Nutation Visualized

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.