HomeHelpContact usBack

Modules Open College - e-Learning Content Library
 
Solar Eclipse
 

The condition when the Moon covers the Sun as the Moon crosses the ecliptic plane during the new Moon phase is known as the solar eclipse. A solar eclipse is a beautiful and rare phenomenon.

A total eclipse occurs when the lunar disk covers the solar disk completely. The Moon in perigee is 21,000 km closer to the Earth, compared to the average distance. The Moon is 21,000 km farther than average in its apogee. The ecliptic nature of the lunar orbit causes the Moon's angular position to change.

If the angular diameter of the lunar disk (which is around 0.5?) is slightly smaller than the angular diameter of the solar disk (which is around 0.5? too), then a bright narrow ring is the only visible part of the Sun during the apogee of the eclipse. Such eclipse is called a ring-shaped eclipse. The Sun may also be partially covered by the lunar disk because of a lack of convergence of their centers in the sky. Such eclipses are known as partial eclipses.

A magnificent phenomenon known as the corona may be observed only during total eclipses. Observations of the corona still make significant contributions to our understanding of astronomy. Astronomers from many countries travel to the locations of total solar eclipses to study that phenomenon.

A solar eclipse begins with sunrise in the Western areas of the Earth's surface, and it ends in the Eastern areas during sunset. A total solar eclipse normally lasts for several minutes (a maximal duration of total solar eclipse, equal to 7 minutes 29 seconds, will occur on July 16th, 2186). Solar eclipses may only be observed in those regions of the Earth where the Moon's umbra strip is passing. The umbra's diameter cannot exceed 270 km, thus, total solar eclipses may only be visible over relatively small sections of the Earth's surface.

Although solar eclipses occur more frequently than lunar ones, solar eclipses are rarely observed at any specific location on the Earth's surface.

This model illustrates a solar eclipse that took place on August 11, 1999. The areas that correspond to the locations where total and partial phases of the eclipse could be observed are shown on the map. You may select an observation location by clicking any of blue circles that designate different cities. You may also select an observation location by choosing a particular city from the list that the model provides.

Press "Run" button to activate the model. Observe the Moon overshadowing the solar disk. The sky grows dark. As the lunar disk completely blocks the solar photosphere, a corona will become visible if you choose an observation location that lies within the total eclipse zone (Bucharest, Teheran). Local city time at the moment of the eclipse is shown in the model's top right corner. Note that the model operates under accelerated temporal conditions, as a total eclipse lasts for several minutes in real time.

Press "Stop" button to bring the animation to a halt. "Reset" button will return the model to its initial state.

 
© OpenTeach Software, 2007