Moon Phase Software

Moon tools

Lunar eclipse calculation methods

A lunar eclipse occurs as the Moon passes through Earth's penumbral and umbral shadows. Previous and next global eclipse peaks bracket a selected UTC instant, while each event's shadow phases determine its type and contact times.

This method hub separates event timing from coverage measures. Contacts and durations describe when shadow phases begin and end. Obscuration describes covered disc area at peak, while umbral magnitude is a different diameter-based catalogue quantity and is not emitted by the current calculator.

Earth shadow and lunar eclipse diagram inside a dark observatory

Calculation sequence

How this method is divided

  1. 01

    The eclipse calculation returns a strictly previous and strictly next peak. Events are penumbral, partial, or total. The nearest result is selected by elapsed time, without treating a larger or total eclipse as automatically nearer.

  2. 02

    Penumbral, umbral, and totality contacts fall symmetrically around the peak by their available semi-durations. Phases that do not occur are absent. These are global events; local horizon and visibility questions require observer coordinates and conditions.

Working sheets

Two focused guides

Method selection

Where this method fits

  • Use the finder to bracket one exact instant with the previous and next global eclipse peaks.
  • Use the position calculator at a contact instant to inspect the Moon against an observer's ideal horizon.
  • Umbral obscuration is covered disc area and is different from the catalogue quantity called umbral magnitude.

Put the method to work

Use the working calculation

Evaluate another exact instant with the calculator described here, or return to the overview for the shared time conventions and supported era.

Open Lunar Eclipse Finder

Method overview · Calculation sources