The word eclipse darkening of the light of one celestial body by another. If we examine the shadow cast by the Earth or the Moon, we discover two regions of different degrees of darkness. The darkest and smallest region is known as the umbra. This region is completely blocked from the Sun during a solar eclipse. The semidark region is called the penumbra. Here a portion of the Sun can be seen. A solar eclipse occurs when the Moon is at or near New Moon and is in line between the Earth and the Sun. The Moon's shadow falls on the Earth. A total eclipse occurs in the umbra region and a partial eclipse in the penumbra. The average length of the Moon's umbra is 373,000 km, which is slightly less than the distance between the Earth and the Moon. From the Earth, the Sun appears slightly larger than the Moon. During total eclipse, a bright ring, or annulus appears around the dark moon. This condition is known as an annular eclipse. The penumbra region may be as large as 104 km in diameter at the surface of Earth, while the maximum diameter of the umbra at the Earth's surface is 270 km. This occurs when the Sun is furthest from Earth (in July) and the Moon is closest, that is at perigee. The shadow of the Moon moves Eastward at a speed f 1600 km/hr. The greatest time for a total eclipse is 7.5 minutes with an average value of 3 to 4 minutes. A lunar eclipse when the Moon is at or near full Moon, and in line with the Sun and the Earth. The shadow of the Earth conceals the Moon. The average length of this shadow is 1.4 x 106 km, and the total eclipse can last 1.5 hours, with a partial eclipse lasting 3 hours and 40 minutes.
Thus, eclipses occur either when the Earth lies between the Sun and the Moon, and its shadow falls on the moon, or when the Moon lies between the Sun and Earth and its shadow falls on the Earth. The former is called a Lunar Eclipse and happens on a full moon, while the latter is called a Solar Eclipse and falls on a new moon. Since the orbit of the Moon around the Earth is at a 5 degree angle, every full moon or new moon will not be an eclipse. Eclipses occur only when the Sun, the Earth, and the Moon are collinear. For photographs and dates of eclipses, click below.
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