As you know, the planets and their satellites are not standing still. The earth rotates around the Sun, and the Moon revolves around the Earth. And from time to time there are moments when the Moon in its motion completely or partially covers the Sun.
Figure 1. Diagram of the solar Eclipse
A solar Eclipse is the moon's shadow on the Earth's surface. This shadow is a diameter of about 200 km, which is many times smaller than the diameter of the Earth. Therefore, a solar Eclipse can be observed only in a narrow strip on the way Moonshadow:
Figure 2. The moon's shadow on the Earth's surface during a solar Eclipse
If the observer is in the band the shadows, he sees a total solar Eclipse, when the Moon completely obscures the Sun. When the sky darkens, and it may become visible stars. Gets a little cooler. Birds abruptly fell silent, scared by the sudden darkness, and try to hide. Animals start to worry. Some plants curl the leaves.
Figure 3. Phase of a total solar Eclipse
Observers that are near band total Eclipse can be seen by private solar Eclipse. In partial Eclipse, the Moon passes through the disk of the Sun is not exactly in the center, and hides only a portion of this disk. When the sky darkens much weaker than in a total solar Eclipse, the stars are not visible. Private Eclipse can be observed at a distance of about 2 thousand kilometers from the zone of total Eclipse.
Figure 4. Private solar Eclipse
A solar Eclipse always occurs at the new moon. At this time the Moon on the Earth is not visible, because the side of the moon that faces the Earth, not the Sun (see figure 1). Because of this, it seems that during an Eclipse the Sun closes a black spot, suddenly, out of nowhere.
The shadow that the Moon casts in the direction of the Earth looks like a sharply converging cone. The tip of the cone is slightly beyond our planet (see figures 1 and 2). Therefore, when a shadow falls on the Earth's surface, it is not the point, and relatively small (150-270 km in diameter) black spot. After the Moon, this spot is moved over the surface of our planet at a rate of about 1 kilometer per second:
A diagram of the solar Eclipse of 22 July 2009 NASA site
Therefore, the moon's shadow with great speed moving along the earth's surface, and can permanently close any one place on the globe. The maximum possible duration of the complete phase - only 7.5 minutes Private Eclipse lasts about two hours.
The solar Eclipse on Earth is a truly unique phenomenon. It is possible because on the celestial sphere diameters of the moon and Sun are nearly identical, despite the fact that the diameter of the Sun is about 400 times the diameter of the moon. And it happens because the Sun is about 400 times farther from Earth than the Moon.
But the orbit of the moon is not round, but elliptical. Therefore, in points, conducive to the occurrence of eclipses, lunar disk can be larger than the sun, equal to or less than him. In the first case comes complete Eclipse. In the second case, there are a total Eclipse, but it lasts only a moment. And in the third case, the annular Eclipse: around the dark disk of the moon can be seen shining ring of the Sun's surface. This Eclipse can last up to 12 minutes.
During a total solar Eclipse is possible to observe the solar corona - the outer layers of the Sun's atmosphere, which in ordinary light of the Sun is not visible. This is a stunningly beautiful sight:
Figure 6. Solar Eclipse August 11, 1999
Read also: How often you get a solar Eclipse?