Input, select, or point to your location for the eclipse.
Then press the Do the Calculation button.

The map shows the eclipse path across the Earth. The path is shown by a red line with green lines depicting the northern and southern limits of totality. The dot marker indicates a specific position or location.

Locations can be selected from a list. These locations are pre-stored in the program and are intended to simply show key points or cities along the path of totality. Input your location by either manipulating the dot marker on the map with the pointing device, selecting one from the list, or by typing in the coordinates directly.

You can enter latitude and longitude in degrees/minutes/seconds, degrees/minutes, or just degrees. Decimal places are allowed. For example, the value 10 degrees, 12 minutes, 45 seconds can be input as 10d 12m 45s, 10d 12.75m, or 10.2125 d.

UT is coordinated universal time. Enter the number of hours (+/-) from UT to your local time zone. Pre stored locations already have the UT offset stored. Set the UT offset to zero for results in UT.

Lunar Limb Profile analysis is included in the calculations. The position of the moon and its orientation towards the observer are taken into account to obtain a detailed profile. The profile is compared again the position of the Sun to find the valleys and peaks along the edge that will contribute to Baily's Beads.

When the Do the Calculation button is pressed thousands of computations are performed to determine the exact contact times for the location you supply. These contact times are displayed on the map as the page is regenerated. Below the map you will find more details about the eclipse including a figure showing Baily's Beads at one second before (and after) the primary contacts for totality. After the calculations have been run other eclipse chaser resources for the location just calculated are made available such as a count down timer and Lunar Limb Profile graphics.

The Solution at dot marker shows the duration and time at central eclipse (or partial coverage information) for the current dot marker position. Move the dot marker by picking a point on the map or dragging it there. The duration computation does not include the center of figure and lunar limb correction available when the Do the Calculation button is pressed.

Select a different eclipse path has a list of the solar eclipses known to this program. Additional solar eclipses can be added by request. Eclipse names that start with an "A" are annular eclipses. "E" names are total solar eclipses. Eclipses are listed by year and month abbreviation. To select a different eclipse, pick it from the list and press the Select button.

Understanding the Results: Results from pressing the Do the Calculation button are displayed both on the map and web page for the four primary contacts. First contact (C1) is when the partial eclipse starts. Second contact (C2) is the beginning of totality. Third contact (C3) is the end of totality. Fourth contact (C4) is when the partial eclipse ends. The results show the time of each major contact to the tenth of a second. The altitude above the horizon for the sun is provided with each contact in degrees. Zero degrees is right on the horizon. Ninety degrees is directly overhead.

Directly below the map you can see the current location of the cursor/pointer as it is moved around the map. After calculating an initial result, click on another location and the distance from the "C" marker to the new marker point is shown in kilometers and miles.

The graphic below the map depicts the lunar limb (exaggerated 10x) at the time of eclipse. This is useful for determining limb corrections as well as where the diamond ring and Baily's beads will appear.

All computations assume a stationary observer. Relative speed (such as in aircraft and ships) are not accounted for when computing circumstances.

Refraction: Atmospheric refraction of light applies only to eclipses that are near the horizon. Eclipses that are less then ten degrees in altitude will be slightly higher in the sky. This calculator does not currently account for atmospheric refraction which can be as much as half a degree (a full lunar diameter) right on the horizon. Fortunately the closer the sun is to the horizon the more refraction helps make it look higher in the sky. When the calculator indicates an eclipse that is at zero degrees in altitude, it will actually appear to be half a degree up from the horizon. The calculator will display "NV" for Not Visible when the eclipse contact is below the horizon.

Time information: The calculations use UTC (Coordinated Universal Time). If you are using a GPS please note that time data may be in GPS time and not UTC when the GPS is first turned on. Leap second updates are sent to the GPS network about every quarter hour and if your GPS is set up to work with the data then the clock will be updated. GPS time is over ten seconds ahead of UTC. To learn the current GPS offset as well as other time systems click here.

Calculation Method: Elements used in the calculations are based on the lunar center of mass as determined by NASA/JPL using the DE200/LE200 ephemeris. The position of the center of mass (as seen by an observer on Earth) is slightly different than the actual "center of figure" which shifts depending on libration (slight wobble of the moon) and the position on Earth of the observer. The actual center of lunar mass is about 2 kilometers closer to Earth. Views from various points along the eclipse path see a different profile of the moon. The resulting shift means that the observed position of the moon can be almost 0.5 seconds of arc different than the calculated center of mass position. For the majority of eclipses the deviation is less than a second in totality duration time.

Lunar Limb Profile Corrections: When the lunar limb corrections are incorporated the actual observed center of figure is determined and used. Corrections may be several seconds of time at either or both 2nd and 3rd contacts. The majority of the correction value is the result of the lunar profile.

To compute the corrections this program uses either the Watts Lunar Limb Profile data from CDS along with correction algorithms developed through the study of a large data set of lunar-stellar occultation timings (links below) or a more recent set of data provided by Dave Herald after reducing laser altimeter readings from the Japan Aerospace Exploration Agency's (Kaguya) Selene lunar orbiter. The difference between the center of mass and center of figure are also included. When run the program reads a copy of the Watts or Kaguya/Herald data on the eclipse-chasers server and creates a list of points every 0.2 degrees describing the profile. The profile is then compared against a sliding circle that represents the solar disk. When the disk of the sun is completely obscured the eclipse is total and the amount of shift required determines the time change. The approach compares favorably with other methods of contact corrections and better accounts for profile features near, but not exactly at, the computed points of contact.

The Kaguya/Herald profile was derived from the Kaguya Laser-altimeter time series dataset by Dave Herald of Canberra Australia. It provides the angular height of the lunar limb above a mean lunar limb centered on the center of mass of the moon, with the moon being at its mean distance. The dataset has been tested against the historical list of lunar occultations to validate the accuracy of the conversion. The reference point for the lunar profile is the center of mass of the moon. When using the dataset the position of the moon as derived from DE421 (or previous versions of the JPL Development Ephemeris) does not need to be corrected for any difference between center of mass and center of figure.

Graphic Presentation: The eclipse path shown inside Google Maps is an approximation. The path was generated with an elevation of zero meters above sea level and does not account for terrain changes. Specific location input for the latitude and longitude are processed by a different calculation for the local circumstances. The centerline graphics are meant to serve as a general guideline to the eclipse path. In some places the actual edge or center may be shifted by several kilometers. Use the Do the Calculation button to determine local circumstances that account for elevation and the lunar limb profile.

Baily's Beads: When the photosphere of the sun peeks through valleys along the lunar profile a series of bright points of light are visible. The rugged profile of the moon can sometimes cause a string of bright points just as the eclipse goes total (or the total phase ends). The term "beads" was first coined by the 19th century British eclipse chaser Francis Baily hence they are known as Baily's Beads. A side effect of the lunar limb profile correction calculation is that the same data can be used to render Baily's Beads configurations for times near the umbra contacts. Comparisons to actual observed bead configurations are welcomed by the web master of eclipse-chasers.

Elements Data - The Besselian Elements used by the calculator can be supplied from various sources. Most of them come from the NASA GSFC web site. The common aspect is that they all use the center of mass for the moon. Very short eclipses and grazing eclipse conditions are difficult to predict well in advance. The accuracy of the calculation needs to be verified by multiple sources. If you notice that the elements data in use is out dated or that a more recent set of exists then please alert the webmaster so that the files can be updated.

Acknowledgements: Written 2008/2009 by Bill Kramer using the HTML/PHP/Javascript programming languages. The following were important contributors to the programming.

• Elements of Solar Eclipses 1951-2200 by Jean Meeus.
• Textbook on Spherical AstronomySpherical Astronomy by W.M. Smart.
• A Manual of Spherical and Practical Astronomy V-1 by William Chauvenet
• The Mathematical Theory of Eclipses According to Chauvenet's Transformation of Bessel's Method by Roberdeau Buchanan
• Explanatory Supplement to the Astronomical Ephemeris (1974 printing)
• Besselian elements and expert guidance provided by Fred Espenak, NASA's GSFC.
• Mapping system courtesy of Google Maps.
• Lunar Exploration Program at JAXA. Data processed and provided by Dave Herald for eclipse prediction purposes.
• Lunar limb-profile data obtained from CDS/Vizier/122.
• Analysis of Lunar Occultations by Morrison and Appleby.
• Additional input and valuable feedback provided by Glenn Schneider, Dave Herald, Fred Espenak, Michael Zeiler, Xavier Jubier, Raymond Dubois, and John Irwin - Thanks!

Do you have a location to suggest or did you find a bug in the data/calculation/description? Send email with the eclipse date/month, location name, latitude, longitude, elevation, and UT hour offset. Clear sky!