The instant of greatest eclipse occurs when the distance between the Moon's shadow axis and Earth's geocenter reaches a minimum. It's usually expressed at greatest eclipse. Eclipse magnitude is strictly a ratio of diameters and should not be confused with eclipse obscuration which is a measure of the Sun's surface area occulted by the Moon. Eclipse obscuration is defined as the fraction of the Sun's surface area occulted by the Moon.
Fourth contact is the instant of last external contact and it marks the end of the partial eclipse.
V is defined as the contact angle measured counter- clockwise from the zenith point of the Sun's disk. This occurs at and defines the instant of greatest eclipse. Gamma takes on negative values when the shadow axis is south of the Earth's center. The chart is not directly comparable with Figures 9 to 11 because of national differences in data collection. However the patterns of heavy and light cloudiness are similar.