Explanation of Solar Eclipse Data Tables
by Fred Espenak
The following tables contain brief explanations for the various parameters used in the prediction of solar eclipses.
| Eclipse Characteristics |
| Parameter |
Description |
| Eclipse Magnitude | the fraction of the Sun’s diameter occulted by the Moon at the instant and geographic location of Greatest Eclipse;
the Eclipse Magnitude is less that 1.0 for partial and annular eclipses; the Eclipse Magnitude is equal to or greater than 1.0 for total eclipses |
| Eclipse Obscuration | the fraction of the Sun’s area occulted by the Moon at the instant and geographic location of Greatest Eclipse;
the Eclipse Obscuration is less that 1.0 for partial and annular eclipses; the Eclipse Magnitude is equal to or greater than 1.0 for total eclipses |
| Gamma | the distance (in units of equatorial Earth radii) of the Moon’s shadow axis from the center of Earth at the instant of Greatest Eclipse; since this is the instant when the Moon passes closest to the center of Earth, Gamma is, by definition, the minimum distance of the lunar shadow axis from center of Earth
|
| Conjunction Times |
| Parameter |
Description |
| Greatest Eclipse | the instant when the axis of the Moon’s shadow passes closest to the center of Earth
(by convention the date of an eclipse is fixed to this instant) |
| Ecliptic Conjunction | the instant when the Sun and Moon have the same ecliptic longitude; this defines the instant of the New Moon phase |
| Equatorial Conjunction | the instant when the Sun and Moon have the same celestial longitude in the equatorial coordinate system; this is the instant when the Sun and Moon have the same Right Ascension |
| Geocentric Coordinates of Sun and Moon |
| Parameter |
Description |
| Right Ascension | the longitudinal position (in the equatorial coordinate system) of the Sun and the Moon at the instant of greatest eclipse |
| Declination | the latitudinal position (in the equatorial coordinate system) of the Sun and the Moon at the instant of greatest eclipse |
| Semi-Diameter | the apparent angular radius of the disk of the Sun or Moon at the instant of greatest eclipse |
| Eq. Hor. Parallax | Equatorial Horizontal Parallax, the angle subtended by the radius of the Earth at the distance of the Sun or Moon at the instant of greatest eclipse |
| Geocentric Libration of Moon |
| Parameter |
Description |
| l | the Moon’s geocentric libration in longitude at greatest eclipse |
| b | the Moon’s geocentric libration in latitude at greatest eclipse |
| c | the Moon’s geocentric libration in position angle of lunar rotation axis with respect to celestial north |
| Prediction Paramaters |
| Parameter |
Description |
| Ephemerides | identifies the ephemerides used to calculate the postions of the Moon and Sun |
| ΔT | the value of ΔT used in the eclipse predictions |
| k (penumbra) | the mean radius of the Moon measured in equatorial Earth radii and used in calculating the size of the penumbral shadow |
| k (umbra) | the mean radius of the Moon measured in equatorial Earth radii and used in calculating the size of the umbral shadow |
| Saros Series | the Saros series number followed by the sequence number and total number of eclipses in the series |
