Footnote

a Since the orbits of the moon and the earth are elliptic, the apparent size of the sun and the moon vary a little according to where they are in their orbits. When the moon is at the point in its orbit farthest from the earth, the darkest part of the moon’s shadow may not quite reach the surface of the earth. When this occurs, observers on earth who are in line with that shadow experience an annular eclipse, with the sun visible as a bright ring around a dark shadow.