If you prefer to view the applets offline, you can download them. Just unzip astro-applets.zip, and open astro-applets.html in your browser.
If you can't run this applet properly, please download the latest version of the Java Runtime Environment (JRE) at java.com.
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.
I have recorded a video clip that explains this applet. It's available in several formats.
If you can't get any sound in the QuickTime file, you may need to download the latest version of QuickTime.
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.