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Motion of the Sun
 

The Sun, as any other luminary, rises above the horizon at the eastern side of the skyline every day, and sets at the West. The Sun reaches its maximum elevation at noon (local time). Lower transit occurs at midnight. In the polar areas, the Sun does not set in summer; and its lower transit point may be observed.

The visible daily path of the Sun is either decreasing or increasing in mid-altitudes. The Sun's altitude is minimal at winter solstice (approximately on December 22) and it is maximal at summer solstice (approximately on June 22). The length of the day is equal to the length of the night at the times of spring and autumnal equinoxes (March 21 and September 23, respectively) since the Sun is at the celestial equator's intersection with the ecliptic.

This model illustrates all the major lines and points of a celestial sphere: the horizon, the polar axis, zenith and nadir, celestial equator, ecliptic, equinox and solstice points. A large yellow circle outlines the Sun's current position.

Press the "Run" button to activate the model. Watch the Sun and the ecliptic move around the celestial sphere in a Diurnal Motion mode. Variations in the background color outline the changes between day and night. A separate window displays the virtual date and time.

Annual Motion mode records time and displays the annual motion of the Sun along the ecliptic. Use the latitude input window to adjust the observation point's latitude, and increases it up to 60? to observe the phenomena of polar day and polar night. (60? latitude corresponds to the location of the polar circle).

 
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