The Motion of the Sun Along the Ecliptic

Applet

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If you can't run this applet properly, please download the latest version of the Java Runtime Environment (JRE) at http://java.sun.com/j2se/.

This applet was made together with Tey Meng Khoon and Frederick H. Willeboordse of CITA (Centre for Information Technology and Applications) for the course Heavenly Mathematics: Cultural Astronomy.

Video Clip

I have recorded a video clip that explains this applet. It's available in several formats.

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  RealVideo SureStream, click on the embedded player or click on the link to view in a separate window. The quality and file size of the clip is determined by the preference settings in your RealPlayer.
• RealVideo LAN/150Kbps, click on the link to view in a separate window or right-click to download and view it from your hard disk. This file is big, so this is only for people with fast connections.
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  QuickTime, click on the picture to view in a separate window or right-click the link to download and view it from your hard disk. This file is big, so this is only for people with fast connections.

If you can't get any sound in the QuickTime file, you may need to download the latest version of QuickTime.

Discussion

This Java applet shows the motion of the Sun along the ecliptic. It is similar to “The Apparent Motion of the Sun” applet, but here we have added the zodiac.

Notice how the sun moves backwards along the ecliptic in the course of the year. What I want you to understand is how the “spiral of circles” is caused by the daily motion of the ecliptic and the annual motion of the sun along the ecliptic.