WHAT IS ?

SOLAR ECLIPSE

A curious mix of celestial sizes, distances and orbits make solar eclipses possible.
"The Sun is far larger than the Moon -- about 400 times larger in diameter," explains James C. White II, executive director of the Astronomical Society of the Pacific. "Yet a happy circumstance is that the Sun is also about 400 times farther from the Earth than the Moon."
This makes the Moon and Sun appear roughly the same size in the sky. When the Moon's orbit about the Earth takes it directly between the Sun and us, the Moon can obscure all or part of the Sun. Exactly what happens depends on minor changes in distance and position.
Orbits are not perfectly circular, but instead are slightly egg-shaped, so the distance between the Earth and the Sun changes as Earth orbits around its host star, and the same thing happens as the Moon revolves around our planet.
Eclipse Terms
Partial eclipse The Moon covers only part of the Sun. Total eclipse The Moon covers the entire disk of the Sun along a narrow path across the Earth. Annular eclipse The Moon is too far from Earth to completely cover the Sun. A thin ring of the Sun's disk surrounds the Moon.
Also, the Moon's orbit around Earth is tilted, so much of the time the Moon is above or below our line of sight to the Sun, making an eclipse impossible. When the three bodies line up just right, which only happens at a new Moon and when the lunar orbit is in the proper point of its orbital plane, an eclipse can occur.
If things are aligned just right, a total eclipse occurs. There are at least two solar eclipses (partial, total or annular) per year somewhere on Earth, researchers say, and the maximum number of all eclipses that can occur in a year is five. Total solar eclipses happen about once every 1.5 years.
But Earth is a big place, and these total eclipses can be rare in any given location.