Explanation of Lunar Eclipse Contact Tables

by Fred Espenak

The following tables contain brief explanations for the various contact times and associated parameters used in the prediction of lunar eclipses.


Lunar Eclipse Contacts
Contact Event Contact Description
Penumbral BeginsP1 the instant of first exterior tangency of the Moon with the Penumbra
(Penumbral Eclipse Begins)
Partial BeginsU1 the instant of first exterior tangency of the Moon with the Umbra
(Partial Umbral Eclipse Begins)
Total BeginsU2 the instant of first interior tangency of the Moon with the Umbra
(Total Umbral Eclipse Begins)
Greatest Eclipse- the instant when the center of the Moon's disk passes closest to the axis of Earth’s shadows
Total EndsU3 the instant of last interior tangency of the Moon with the Umbra
(Total Umbral Eclipse Ends)
Partial EndsU4 the instant of last exterior tangency of the Moon with the Umbra
(Partial Umbral Eclipse Ends)
Penumbral EndsP4 the instant of last exterior tangency of the Moon with the Penumbra
(Penumbral Eclipse Ends)

The following parameters are given for each eclipse contact.
  • Time TD - the Terrestrial Dynamical Time (TD) of the event
  • Time UT1 - the Universal Time (UT1) of the event
  • Zenith Latitude - the geographic latitude where the Moon appears in the zenith
  • Zenith Longitude - the geographic longitude where the Moon appears in the zenith
  • Position Angle - the position angle of Moon with respect to the center of the shadow measured counter-clockwise from celestial north
  • Axis Distance - the geocentric angular distance (degrees) of the center of the Moon from the axis or center of the shadow

Eclipse Durations
Parameter Description
Penumbral (P4 - P1) the elapsed time (hours, minutes, seconds) between the penumbral contacts P1 and P4; this is the duration of the penumbral phase for penumbral eclipses; for partial and total eclipses, this period encompasses the entire eclipse (including all penumbral, partial and total phases)
Partial (U4 - U1) the elapsed time (hours, minutes, seconds) between umbral contacts U1 and U4; this is the duration of the partial phase for partial eclipses; for total eclipses, this period encompasses the entire umbral eclipse (including all partial and total phases)
Total (U3 - U2) the elapsed time (hours, minutes, seconds) between umbral contacts U2 and U3; this is the duration of the total phase for total eclipses