Earth SystemsPolar Motion Monitor HomepagePolar Motion Monitor

Wobble Tracker

by Davis Chapman

wobtrac_98-2001min.gif (5322 bytes)

The current location of the pole as of April 1, 2001  is shown by the leftmost tip of the spiral. The spin axis of the Earth (North Pole) constantly changes location in a spiral form which is known as Chandler's Wobble.  The North Pole constantly spirals in and out in a 6.5 year cycle to form small circles nested inside larger ones.  This spiral for 2001 is not normal  It probably shows a strong skewing towards the left which means that the entire plot of Chandler's wobble (which means the average location of the spin axis or North Pole of the Earth) may be moving or drifting at a much more more rapid rate than the past towards Y+, which means Longitude West 90 (through the Great Lakes). The X+ equals the Greenwich Meridian (through England).

The Amazingly Fun Way To Track Chandler's Wobble
and make correlations with tectonic activity

Use the Wobble Tracker to find what changes in Chandler's Wobble are connected with world volcanism, such as the peaks and valleys which are shown in this chart.

Chart: The Tempo & Rhythm In World Volcanism Compared With The X Wave 1890-1993

Table103_PM_World_volcanism_correlation_1890_1993.gif (21588 bytes)

Quite clearly the rhythm of   worldwide volcanic activity directly reflects the tempo of the 6.5 year X Wave in Chandler's Wobble. This same direct correlation can be seen when just the activity in major arcs and groups of volcanoes is charted.  Similar correlations can be found with earthquake activity.  You can use the Wobble Tracker to see what was happening to the spiraling motion of the spin axis at the same time as these tectonic events.  To see same sample charts on which you may find some correlations with world volcanism, click here.

Wobble Tracker is available for downloading over the internet for $15.00 or is available on a CDROM for $18.00  To order go to the How To Obtain The Phoenix Trilogy & Other DocumentsCosmic Catalog

More Technical Details

Wobble Tracker 1.0

Wobble Tracker is a shareware program that enables you to see Chandler's Wobble on a 2-D chart. The purpose of this is so that you can view the wobble and see how much drift the pole position is undergoing, along with the direction of the drift. All data included with Wobble Tracker is publicly available from the IERS Web site (, and the Wobble Tracker has the functionality built in to download the latest wobble data so that you can keep up-to-date on the state of the pole position. The X+ line is the Greenwich meridian. The Y+ line is on the 90-degree West meridian, passing through North America.

This application was created for the use of individuals for monitoring the current state of Chandler's Wobble. It is intended to enable the user to see the direction and amount of drift has taken place in the location of the pole over time.

For technical support, registered buyers can send an e-mail to:

This application has been tested on Windows 2000 and NT 4. It has not been tested on any other Microsoft operating system. If it does not run on your OS, please send an e-mail to the above address, specifying the OS you are running, and a description of the problem you are encountering.

To connect with a user group, send a blank email message addressed to:

Displaying Wobble Data

To display daily wobble data starting with 1962, select the year from the drop-down box labeled "Year To Draw". To draw all daily data, at the bottom of this list is an option for "ALL." Selecting this option will draw all of the daily wobble data starting with 1962.

To draw historical wobble data from 1846 to 1961, select the year from the drop-down box labeled "Historical Year To Draw" and select the number of sequential years to draw from the drop-down box labeled "Number of Years To Draw." Historical data from 1846 to 1889 contains only 10 data points per year. Starting in 1890 through 1961 there are 20 data points per year.

The Draw menu provides options for selecting a color to draw for any years specified after selecting the color. This menu also contains and option to specify the line width to be used when drawing the wobble data. The final option on this menu will clear the current drawing.

The View menu provides options for turning the grid display on and off, along with configuring the scale of the grid, and the scale of the wobble data display. In general, the best settings for the drawing scale are 0.7 to 0.6 range. The default setting for the grid is 0.05, which draws the grid lines at 1/20 arc-seconds, which is slightly more than 5 feet, or a little over 1.5 meters.

A chart of grid settings and their equivalent distances in included in a Readme.txt file, along with all of these instructions.

The File menu provides options for specifying the location of the data files containing the wobble data. By default, this is initialized in a directory called "data" directly below the directory where the Wobble Tracker application has been installed. Another option on the File menu, labeled "Get Data Update" will download the latest daily data file for the current year from the IERS web site and install the data file in the data directory.