A total solar eclipse is visible from some place on Earth around every two to three years. While this seems often, it is still a rather rare occurrence since it's only visible from a narrow path along the Earth. So within a lifetime, any point in the world will likely only see a total solar eclipse every hundred years or so.
A solar eclipse happens when the moon blocks the path from Earth to sun, casting a shadow on Earth. Those areas that get into the darkest part of the shadow, called the umbra, will experience a total solar eclipse. But consider the fact that the moon is 400 times smaller than the sun. How is something so small able to block Sun's light to Earth? It just so happens that although moon is 400 times smaller than the sun, it's also 400 times closer to Earth, giving it the same apparent size as the sun, and allowing it to block the sun's light, giving us a total solar eclipse.
A Total solar eclipse can only take place when the moon is near perigee, the point of the Moon's orbit closest to Earth and the moon is able to completely block the Sun.
An annular solar eclipse occurs when the Moon's disk is not big enough to cover the entire disk of the Sun, and the Sun's outer edges remain visible to form a ring of fire in the sky. An annular eclipse of the Sun takes place when the Moon is near apogee, the point of Moon's orbit farthest from Earth.
If Sun and Earth do not perfectly align and the moon only partially covers the sun’s disk, then a partial solar eclipse occurs with sometimes just a small part of the sun eclipsed.
Between 1951 and 2050, the lower 48 states will only see a total of 8 total solar eclipses. The next one occurs in 2024 and covers 13 states.