The Apparent Motion of the Sun at Different Latitudes

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 < a href="http://java.sun.com/j2se/">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 as seen from the Earth. You can select your geographical position, and you will see how this changes the Sun's path across the sky. The observer is always on “top” of the sphere as indicated by the bright dot on the sphere. The place turns dark when the sun sets but is lighted when the sun rises. You can move the time slider or just let the animation continue to see the motion of the sun in the course of the year. You can slow down the animation to see the effect more clearly.

• What I want to you understand here is how the Sun moves in a spiral of circles up and down. In the course of one day, the declination does not change much, so the path of the sun is almost a circle, but in the course of the year, the declination changes.
• Can you tell when the equinoxes and solstices occur?
• Experiment with choosing different geographical locations. How does this change the length of the day?
• Where and when will there be midnight sun?
• What can you say about night and day at the poles?
• What can you say about where along the horizon the sun rises in the course of the year?
• Do you understand the meaning of the word “Tropics”?
• Do you understand the relationship between this applet and the one that shows the apparent motion of the Sun around the Earth?