Lunar Eclipse Basics

Fred Espenak

Types of Lunar Eclipses

Eclipses of the Moon can only occur when the Moon is near one of its two orbital nodes during the Full Moon phase. It is then possible for the Moon to partially or completely pass through Earth's penumbral and umbral shadows thereby producing an eclipse. There are three types of lunar eclipses:

  1. Penumbral - Moon traverses Earth's penumbral shadow (Moon misses Earth's umbral shadow)
  2. Partial - Moon traverses Earth's penumbral and umbral shadows (Moon does not pass completely into Earth's umbra)
  3. Total - Moon traverses Earth's penumbral and umbral shadows (Moon passes completely into Earth's umbra)

Furthermore, total eclipses can be classified as either central or non-central.

The visual appearance of each of these eclipse types differs dramatically from one another.

The recurrence of lunar eclipses is governed by the Saros cycle. For more information, see Periodicity of Lunar Eclipses.

Lunar Eclipse Dates

By convention, the date and time used to identify a lunar eclipse is the instant of greatest eclipse. This time corresponds to the instant when the center of the Moon passes closest to the axis of Earth’s shadow. While the instant of greatest eclipse is used to indentify an eclipse, the eclipse itself generally lasts several hours and may span across two days.

The instant of greatest eclipse is usually expressed in either Terrestrial Dynamical Time (TD) or Universal Time (UT1). The parameter ΔT is used to convert between these two times (i.e., TD = UT1 + ΔT).

Calendar

The Gregorian calendar (also called the Western calendar) is internationally the most widely used civil calendar. It is named for Pope Gregory XIII, who introduced it in 1582. On this website, the Gregorian calendar is used for all calendar dates from 1582 Oct 15 onwards. Before that date, the Julian calendar is used. For more information on this topic, see Calendar Dates. The Julian calendar does not include the year 0. Thus the year 1 BCE [1] is followed by the year 1 CE (See: BCE/CE Dating Conventions ). This is awkward for arithmetic calculations. Years in this catalog are numbered astronomically and include the year 0. Historians should note there is a difference of one year between astronomical dates and BCE dates. Thus, the astronomical year 0 corresponds to 1 BCE, and astronomical year -1 corresponds to 2 BCE, etc..

Footnotes

[1] The terms BCE and CE are abbreviations for "Before Common Era" and "Common Era," respectively. They are the secular equivalents to the BC and AD dating conventions. (See: Year Dating Conventions )

Links to Additional Lunar Eclipse Predictions

Eclipse Predictions

The eclipse predictions presented here were generated using the JPL DE406 solar and lunar ephemerides. The lunar coordinates have been calculated with respect to the Moon’s Center of Mass.

Acknowledgments

Some of the content on this web site is based on the book Thousand Year Canon of Lunar Eclipses 1501 to 2500. All eclipse calculations are by Fred Espenak, and he assumes full responsibility for their accuracy. Permission is granted to reproduce data from this page when accompanied by an acknowledgment:

"Eclipse Predictions by Fred Espenak, www.EclipseWise.com"