During a particular solar eclipse (when the moon and sun are precisely in line), the eclipse can be either total (sun completely covered) or annular (sun not quite covered) when viewed from the eclipse centerline because:

annular (Sun not quite covered) when viewed from the eclipse centerline

Explanation:

It is when the earth is engulfed in a shadow caused by the moon which is partially or fully blocks the sunlight. This occurs when the sun moon and earth are aligned.  In an annual or partial solar eclipse, only some part of the sun is obscured. Thus looking directly at the sun can be harmful to eyesight. The effect is in the form of a  ring around the sun. In this elliptical orbit, the distance from the sun can vary from 6%. Thought the solar eclipse are rare events, occurring every 18 months of less than 7 min and 2 seconds.