Key to Google Eclipse Maps

Fred Espenak

Introduction

The interactive Google Eclipse Maps each show the path of the Moon's penumbral shadow. This is the geographic region from which a partial eclipse can be seen. The northern and/or southern penumbral shadow path limits are plotted as green curves. The magenta loops represent the locus of all locations where the partial eclipse begins or ends at sunrise or sunset. Inside these regions the partial eclipse is in progress at sunrise or sunset. An orange curve also appears inside this region and represents the locus of all locations where the partial eclipse is at its maximum phase at sunrise or sunset. You MUST be somewhere within the region enclosed by these curves in order to see the partial eclipse. Outside this region no eclipse is visible.

For total, annular or hybrid eclipses, the Google Eclipse Maps also show the path of the umbral (total) or antumbral (annular) shadow. (This path is much narrower than the penumbral shadow of partial eclipse.) The northern and southern path limits are blue and the central line is red. You MUST be somewhere within the central path (shaded zone framed by the blue lines) to see the central phase (i.e., totality or annularity) of the eclipse. The eclipse is longest on the central line (red). The yellow lines crossing the path indicate the position of maximum eclipse at 10-minute intervals.

The green marker labeled GE is the point of Greatest Eclipse. The magenta marker labeled GD is the point of Greatest Duration. This is the location where the total (or annular) eclipse lasts the longest along the entire path. These predictions do not take into account the mountains and valleys along the edge of the Moon. For the sake of speed and simplicity, the effects of the lunar limb profile are NOT used in the Google Eclipse Maps.

You can be hundreds of miles from the theoretical point of Greatest Duration and still enjoy totality or annularity lasting within a second of the maximum possible (as long as you stay within several miles of the central line).

Google Maps uses a close variant of the Mercator projection, and therefore cannot accurately show areas around the poles. As a consequence, eclipse paths at high latitudes will appear highly distorted and may degrade into a series of straight line segments.

Note: Your web browser must have Javascript turned on in order to see a solar eclipse path plotted on Google Maps. See compatible browsers for more information.

User Directions

The zoom bar (left edge of map) is used to change the magnification [1]. The four-way toggle arrows (upper left corner) are for navigating around the map. If you hold your left mouse button down while the cursor is on the map, you can also drag the map around to reposition it. The two map buttons (top right) let you switch between map view and satellite view.

Click anywhere on the map to add a red marker. A popup window appears above the marker with the calculated eclipse times and duration of totality for that location (see explanation of Eclipse Circumstances below). The 'x' in the upper right corner of the popup window closes the popup window. Additional markers can be placed anywhere on the map. Move the cursor over a marker to reveal a popup window with the eclipse times for that position. The predictions in the popup window can also be displayed in a new web page via the Eclipse Times Popup button (bottom right). You can select and copy this infomation to paste into a word processor.

All the markers can be removed by using the Clear Marker button (below the eclipse map). Choose the Large Map check box to produce a bigger map (hint: enlarge the browser window to its maximum size before selecting the Large Map check box). This option is especially useful to users with large monitors.

Below the lower left corner of the map are three readouts. The first gives the geographic coordinates (latitude and longitude) of the map center while the second gives the geographic coordinates of the cursor. The third line gives the distance of the cursor from the last marker. For more information, see Google Eclipse Map Instructions.

Eclipse Circumstances

When you click on the map a red marker is added and a popup window opens giving the Eclipse Circumstances calculated for that location. The predictions in the popup window can be divided into two sections.

In the top part of the window, the decimal Latitude and Longitude of the marker are given. The Eclipse Type (either total, annular or partial) seen from that position is given. The duration of Totality (or duration of Annularity) lists the length of the total (or annular) phase in minutes and seconds. The Eclipse Magnitude is the fraction of the Sun's diameter eclipsed. The Eclipse Obscuration is the fraction of the Sun's area eclipsed.

The bottom part of the window consists of a table listing the times for important stages of the eclipse. The Event column lists eclipse phase, followed by the date and time (both in Universal Time). Finally, the Altitude and Azimuth of the Sun is given for each event. The altitude is measured from the horizon (0°) to the zenith (90°). The azimuth is measured from due North and rotating eastward (North = 0°, East = 90°, South = 180°, and West = 270°).

Important Note: The eclipse predictions in these interactive maps DO NOT include the effects of mountains and valleys along the edge of the Moon. Such corrections for the lunar limb profile may change the contact times and eclipse durations by ~1-3 seconds. The exact location of Greatest Duration may also change by ~10-20 kilometers.

Footnotes

1. This web page approximates the curved eclipse path by using a series or To maintain the validity of this approximation, the maximum zoom level is limited to ~1 mile/inch (~0.7 kilometers/centimeter). This should prevent over-interpretation of the eclipse path accuracy. You can disable the zoom limit using the link by adding the string "?zoom=1" to the URL of a Google Eclipse Map and then reload the map. ↩

Links to Additional Solar Eclipse Predictions

  • Home - home page of EclipseWise with predictions for both solar and lunar eclipses