Total Solar Eclipse

A solar eclipse occurs when a portion of the Earth is engulfed in a shadow cast by the Moon which fully or partially blocks sunlight. This occurs when the Sun, Moon and Earth are aligned. Such alignment coincides with a new moon (syzygy) indicating the Moon is closest to the ecliptic plane. 

In a total eclipse, the disk of the Sun is fully obscured by the Moon.

A total eclipse occurs when the dark silhouette of the Moon completely obscures the intensely bright light of the Sun, allowing the much fainter solar corona to be visible. Also The Moon's umbral shadow is at most 267 km across on the Earth.

Totality lasts at most about 7.5 minutes, with the shadow sweeping rapidly west-to-east.

Only observers in the umbra(Inner core of total darkness, when the disc of the Sun is completely blocked)see a total solar eclipse. Observers in the penumbra (Outer, partial shadow, when Sun's disc is only partly blocked, with a bit peeking over the edge) see a partial solar eclipse.

Everyone else sees nothing.

While we often sketch the penumbra as uniform, in reality the penumbra shades gradually from the completely dark umbra out towards the edges. The reason is simple: as you move outwards away from the edge of the umbra, you will see an increasing fraction of the Sun peeking out from behind the Moon.

Now, the phases observed during a total eclipse are called:

First contact—when the Moon's limb (edge) is exactly tangential to the Sun's limb.

Second contact—starting with Baily's Beads (caused by light shining through valleys on the Moon's surface) and the diamond ring effect. Almost the entire disk is covered.

Totality—the Moon obscures the entire disk of the Sun and only the solar corona is visible.

Third contact—when the first bright light becomes visible and the Moon's shadow is moving away from the observer. Again a diamond ring may be observed.

Fourth contact—when the trailing edge of the Moon ceases to overlap with the solar disk and the eclipse ends.