A solar eclipse happens when the new Moon goes between the Sun and the Earth. The shadow of the Moon falls upon the Earth's surface and a part of the Sun is eclipsed when the Moon covers it. A solar eclipse lasts no more than 7.5 minutes, with the shadow passing quickly west-to-east. The black disk of the Moon, surrounded by what is called a gossamer halo, a two million degree plasm, replaces the Sun’s brightness.
There are three types of solar eclipses, partial, full, and annular. The shadow of the Moon consists of two parts: the penumbra, the outer shadow, within which a partial solar eclipse is visible; and the umbra, the dark inner shadow, within which a total solar eclipse is visible. When the penumbral shadow hits the Earth, a partial eclipse occurs in that region. A partial eclipse cannot be viewed with the naked eye because of its extreme brightness. A filtering device with a small opening should be used to see it or it can be viewed from telescopes at planetariums.
When the Moon's umbral shadow goes across Earth's surface, total solar eclipse occurs. The Moon's umbral track across Earth is called the Path of Totality. This path is usually 10,000 miles long and approximately 100 miles wide, covering less than 1% of the Earth's surface. A total eclipse can only be seen in this narrow path of totality. Because a total eclipse is visible from a narrow track, it can only be seen from one single location every 375 years. An annular eclipse occurs when the umbra does not touch the earth and is too small to cover the Sun, and the shadow takes the form of a ring called the annulus.
There are about 2.4 solar eclipses yearly. The reason a solar eclipse does not occur every 29 and 1/2 days, is because there is a tilt of 5 degrees when the Moon orbits around the Earth and Earth’s orbit around the Sun. Thus, the shadow of the New Moon misses our planet when it passes it. This is because the new Moon's shadow is 232,100 miles long, and 234,900 miles away from the nearest point of the Earth’s surface, missing Earth by about 2,800 miles. The geometry of an alignment, therefore, occurs twice a year, which means that a portion of the Moon’s shadow lands on Earth’s surface and a solar eclipse can be seen.