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| | A solar eclipse occurs when the Moon comes between the observer and the Sun and covers it. Since the Moon glows with a reflected light and before an eclipse, the moon faces us with its dark side, then the new moon, i.e. when the moon is not visible, occurs immediately before an eclipse. An impression is created that the Sun is covered by blackness of an unknown nature. During a solar eclipse, astronauts, who are in orbit, can observe the umbra of the moon on the surface of the earth. Who so ever is present on Earth fall into this umbra and observe a solar eclipse.
The cone of the moon’s umbra, naturally, is less in diameter than the earth; therefore, a solar eclipse can be viewed only on the territory through which the lunar umbra passes during an eclipse. Since the moon’s orbit is elliptic, the distance between the Earth and Moon at the time of an eclipse can be varied, accordingly the diameter of the lunar umbra on the surface of the earth varies. At a sufficiently close position of the moon and the suitable relative positioning of the Earth, Moon and Sun, the cone of the lunar umbra reaches the surface of the earth. Such an eclipse is called a total solar eclipse. The observer on the earth, who is in the pass band, can see the Moon obscuring the Sun completely, the sky becomes dark and stars become visible. It is possible to observe the solar corona, which is not visible during usual bright sun light, around the solar disc, covered by the moon. If the eclipse is viewed by a stationary ground observer, the totality of the eclipse lasts no more than several minutes. The minimum speed of movement of the lunar umbra on the surface of the earth hardly constitutes more than 1 km/sec.
The total eclipse pass band can reach about two hundred km in breadth. Observers, who are closer to the total eclipse pass band, can view it as a partial solar eclipse. During a partial eclipse, the Moon passes around the solar disc not precisely along the centre covering only part of the Sun. Thus, the darkness in the sky is comparatively poorer than during a total eclipse and the stars are not visible. A partial eclipse can be observed by the naked eye from a distance of about 2000 km from the total eclipse zone.
The totality of a solar eclipse is also expressed by the phase F. The maximum phase of a partial eclipse is usually expressed in a hundred fractions of a unit, where 1 - is the total phase of an eclipse. The total phase can be more than a unit, for example 1.01, if the diameter of the visible lunar disc is more than the diameter of the visible solar disc. Partial phases have designations of 0.90, 0.85, etc. At the edge of the lunar penumbra, the phase is equal to 0, i.e F= 0.
The astronomic classification of solar eclipses:
According to astronomical classification, if the eclipse is observed as a total one somewhere on the surface of the Earth, it is called a total solar eclipse. If the eclipse is observed only partially (such thing occurs when moon’s umbra passes near the surface of the earth but does not intersect it), the eclipse is classified as partial. When the observer is situated in the moon’s umbra, he observes a total solar eclipse. When he is in penumbra, he can observe a partial solar eclipse. Apart from total and partial solar eclipses, there are annular eclipses. An annular eclipse occurs when the Sun is closer to the Earth during the eclipse and the umbra passes above the surface of the earth without intersecting it. Visually, during an annular eclipse, the moon passes along the sun’s ring but appears to be smaller than the sun with respect to diameter and cannot obscure the sun completely. In a maximum eclipse phase, the Sun is obscured by the Moon but the bright ring (annulus) of the uncovered portion of the solar ring is visible round the Moon. During an annular eclipse, the sky remains bright, the stars do not appear and it is not possible to view the Sun’s corona.
Phenomena during solar eclipses:
Shadow bands;
Baily beads;
Diamond ring;
Crescent-shaped umbra (camera obscura);
Decrease in atmospheric temperature;
Radiant ring.
Solar Eclipse in the news: Scientists are gathering with tourists the world over to take in the first total eclipse of the sun in years. The eclipse will be a solar show that will sweep northeast, beginning in Brazil and heading to Mongolia. The sun will be blotted out across large swathes of the world's poorest lands. The last such eclipse of the sun was in November of 2003. It was visible from most of Antarctica, according to Alex Young who is a NASA scientist involved in solar research. The eclipse will block the sun over some very highly populated areas, including West Africa. NASA has advised that it won't be visible from the United States. The moon is expected to first begin blocking out the sun during the morning hours in Brazil before the path of greatest blockage migrates to Africa, then onward to Turkey and finally up towards and into Mongolia. The eclipse will fade out with the sunset at that location. With the eclipse, superstition will follow around the world, as it has for generations and generations. One Indian newspaper continued the superstitions and advised pregnant women not to go outside during the eclipse to avoid having a blind baby or one with a cleft lip. Another of the superstitions that is making the rounds sets forth that food cooked before the eclipse should be thrown out afterward because it will be impure. Another sets forth that those who are holding a knife or ax during the eclipse will cut themselves, as was reported in the Hindustan Times.
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