Solar Eclipse Computer: U.S. Cities and Towns

This form is for U.S. cities and towns only.  For all other locations, in the U.S. or worldwide, specify the latitude and longitude using this form. You can obtain the circumstances of recent and upcoming solar eclipses by following these simple steps:

• Select the eclipse from the first pop-up list.
• Specify the location, using the fields provided in the form.
• Click the "Get data" button at the end of the form to compute a table of local circumstances.
• Be sure to read Notes on the Data (at the end of the form) for an explanation of the items in the table.

For general information on eclipse circumstances and visibility, see Upcoming Eclipses of the Sun and Moon.

Notes on the Data:

The place name you enter above must be a city or town in the U.S. The place's location will be retrieved from a file with over 22,000 places listed. Either upper- or lower-case letters or a combination can be used. Spell out place name prefixes, as in "East Orange", "Fort Lauderdale", "Mount Vernon", etc. The only exception is "St.", which is entered as an abbreviation with a period, as in "St. Louis". You need only enter as many characters as will unambiguously identify the place.

The table of local circumstances gives the UT1 time of each eclipse "event" that is visible from the location. The altitude and azimuth of the Sun at each of the events is given as well. The azimuth is reckoned eastward from North. The altitude is corrected for refraction assuming standard atmospheric conditions.

The computation of Eclipse Local Circumstances is started by iteratively computing topocentric positions of the Sun and Moon to find the time of Maximum Eclipse. Another series of position computations is performed going backwards and forwards from the time of Maximum Eclipse to find the times of contacts. The solar and lunar angular diameters are calculated at each position (using radius values from DE405 (Sun 696000km; Moon 1737.4 km) to determine if contact conditions have occurred. Lunar limb profiles and center of mass/center of figure corrections are not used.

After contact times have been computed, a check is made to determine of Sunrise and/or Sunset occurred during the course of the eclipse. If so, the time of Sunrise and/or Sunset is computed.

The body of the table contains the time of each contact point, the Sun's topocentric position at that time, and its Position and Vertex Angles. The time of sunrise or sunset is also noted in the table if it occurs during the eclipse. The summary at the bottom contains the Duration, Magnitude, and Obscuration.

The Position Angle of a given contact point on the solar limb is measured eastward (counterclockwise) around the solar limb, from the point on the Sun that is farthest north.

Vertex Angle is similar to Position Angle, except that it is measured from the point on the Sun that has the highest local altitude.

Duration is the amount of time from the beginning of the eclipse to the end.

Duration of Totality is the amount of time from the beginning of the central phase eclipse to the end of the central phase. For an annular solar eclipse, it will read Duration of Annularity .

Magnitude of the eclipse is the fraction of the apparent diameter of the solar disk covered by the Moon at the time of greatest phase, expressed in units of solar diameter.

Obscuration is the percentage of the area of the apparent solar disk obscured by the Moon at maximum eclipse.

More information on eclipses can be found at the USNO Eclipse Portal.

For information on the definitions of terms used, see Rise, Set, and Twilight Definitions. If you need to check the times of sunrise and sunset around the time of the eclipse, see Complete Sun and Moon Data for One Day.