A total solar eclipse has foul-stages: first contact, second contact (or start of totality), third contact (or end of totality), and fourth contact.
In your eclipse-trip planning, check astronomy magazines and almanacs for the exact time ot each stage.
The eclipse begins at first contact, the moment when the lunar disk first touches the solar one. First contact can be detected only through a telescope prepared for solar viewing.
Over the next hour, the partial phase unfolds, as the Moon steadily creeps across the Sun. At first, there is little apparent change. But then you will notice a difference in the quality of the light. Shadows grow sharper, while the light becomes more like that on an overcast day. The air grows cooler, and insects, birds, and other animals begin to act as if it is nightfall. If you are standing near a tree that is in leaf, look down. The small gaps between the leaves act like pinhole lenses, throwing hundreds of images of overlapping crescent Suns onto the ground.
The diminished light may tempt you to look at the Sun with the naked eye, but the Sun is still bright enough to damage your vision.
A few minutes before second contact—the start of totality—changes begin to occur in rapid succession. The sky grows quite dark, and the air feels distinctly cool. A breeze usually picks up, perhaps blowing dust across delicate equipment. In the gloom, observers may fumble over camera settings.
Then, the last rays of sunlight stream through walley on the edge of the moon, a phenomenon called Bailey's beads, after an English solar observer, FRancis Baily, who first described them, in 1836. The last beads may linger a moment, creating what is known as the diamond-ring effect. Then comes a flash of pinkish light from the chromosphere, the first layer above the sun's surface- and totally begins.