HMNAO Eclipse Portal

Explanatory Material

Solar Eclipse diagrams

Information on solar eclipses is presented in the form of a diagram consisting of two parts. The upper panel shows the umbral and penumbral shadows of the Earth as an orthographic projection. The lower panel gives timing and positional information on the progress of the eclipse. The solar eclipse of 2001 June 21 is used in the example below.

The title of the upper panel includes the type of eclipse, its place in the sequence of eclipses, both solar and lunar, for the year and the Greenwich calendar date of the eclipse.

Each diagram has up to three types of shading. In those areas where no shading is present, the eclipse is not visible. Those regions in the umbral or antumbral shadow are shaded dark grey. The movement of these shadows correspond to the paths of totality and annularity respectively. In the case of a hybrid or annular-total eclipse, both annular and total eclipses can be seen depending the observer's position along the path. The region encompasses those areas of the globe where the eclipse irrespective of its type will be seen as a partial eclipse is shaded medium grey. Finally, the light grey regions indicates those areas where the whole eclipse is not visible because the Sun is either rising of setting during the course of the eclipse. Where both the northern and southern limits to the penumbral shadow exist, the regions where the Sun rise and sets are separate teardrop-shaped lobes. Where only one penumbral limit exists and in partial eclipses, these lobes are joined in a distorted "figure of eight".

In this particular example, no southern penumbral limit exists and the regions where the Sun rises or sets during the eclipse are joined close to where the Greenwich Meridian crosses the coast of Antarctica. The line bisecting these regions denotes where maximum eclipse takes place at either sunrise (western lobe) or sunset (eastern lobe). Those observers in the western half of the western lobe e.g. northern Argentina, will see less than half of the eclipse after sunrise whereas observers in the eastern half of the western lobe e.g. southern Brazil, will see more than half of the eclipse after sunrise.

A symbol showing the location at which the Moon's shadow makes its first contact with the Earth is denoted by . Similarly, the last contact of the Moon's shadow with the earth is denoted by . In the case of a partial eclipse, the location of greatest eclipse is denoted by . The value of ΔT used for the calculation of the eclipse circumstances is given below the diagram. Country boundaries are also provided to assist the user in determining the visibility of the eclipse at a particular location.

The bottom panel provides a summary of the times and locations of the global circumstances of the eclipse. The symbols used in the main diagram and described above are given next to the appropriate entry in the summary. All times are given in Universal time.