Explanation of Lunar Eclipse Data Tables
by Fred Espenak
The following tables contain brief explanations for the various parameters used in the prediction of lunar eclipses.
| Eclipse Characteristics |
| Parameter |
Description |
| Penumbral Eclipse Magnitude | the fraction of the Moon’s diameter occulted by Earth’s penumbral shadow at the instant of Greatest Eclipse;
the Penumbral Eclipse Magnitude is less that 1.0 for partial penumbral eclipses (and equal to or greater than 1.0 for total penumbral eclipses); the Penumbral Eclipse Magnitude is equal to or greater than 1.0 for most partial eclipses and for all total eclipses |
| Umbral Eclipse Magnitude | the fraction of the Moon’s diameter occulted by Earth’s umbral shadow at the instant of Greatest Eclipse;
the Umbral Eclipse Magnitude is less that 1.0 for partial eclipses (and less than 0.0 for penumbral eclipses); the Umbral Eclipse Magnitude is equal to or greater than 1.0 for total eclipses |
| Gamma | the distance (in units of equatorial Earth radii) of the center of the Moon’s disk from the center of Earth’s umbral shadow at the instant of Greatest Eclipse; since this is the instant when the Moon passes closest to the axis of Earth’s umbral shadow, Gamma is, by definition, the minimum distance of the shadow axis from center of the Moon
|
| Epsilon | the apparent geocentric angular distance (in degrees) of the center of the Moon’s disk from the center of Earth’s umbral shadow at the instant of Greatest Eclipse; Epsilon is, by definition, the minimum angular distance of the Moon from the shadow axis during a lunar eclipse
|
| Conjunction Times |
| Parameter |
Description |
| Greatest Eclipse | the instant when the Moon’s disk passes closest to the center of Earth’s shadow
(by convention the date of an eclipse is fixed to this instant) |
| Ecliptic Opposition | the instant when the Sun and Moon have ecliptic longitudes differing by 180° this defines the instant of the Full Moon phase |
| Equatorial Opposition | the instant when the Sun and Moon have celestial longitudes differing by 180° in the equatorial coordinate system; this is the instant when the Sun and Moon Right Ascensions differing by 12 hours |
| 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 geocentric 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 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 |
| Earth’s Shadows |
| Parameter |
Value |
| Penumbral Radius | the apparent geocentric angular radius (in degrees) of Earth’s penumbral shadow at the distance of the Moon at the instant of Greatest Eclipse |
| Umbral Radius | the apparent geocentric angular radius (in degrees) of Earth’s penumbral shadow at the distance of the Moon at the instant of Greatest Eclipse |
| Prediction Parameters |
| 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 |
| Shadow Rule | the computational method used for enlarging Earth's radius to compensate for the effects of the atmosphere on eclipse contact times; see Earth’s Shadow for more information |
| Shadow Enlargement | the fractional enlargement of Earth's penumbral and umbral shadows used in the eclipse predictions; see Earth’s Shadow for more information |
| Saros Series | the Saros series number followed by the sequence number and total number of eclipses in the series |
