Solar Eclipse Computer
This data service calculates the circumstances of recent and upcoming
solar eclipses
(2017 - 2024). Use the following
steps to find the visible circumstances at any given location:
- Select the eclipse from the first drop-down list.
- Specify the location of interest using the fields provided
on the form. Use the buttons
to find coordinates of cities or towns in the U.S. or its territories,
or to convert between Degrees-Minutes-Seconds (DMS) and Decimal Degrees.
- Click the "Get Data" button at the end of the form to compute a
table of local circumstances.
Be sure to read the
Notes
on the Data
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
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 adopted by the International Astronomical Union (Sun 696000 km; 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 if 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
Eclipses Online 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.
Application Programming Interface
This data service uses one of our Application Programming Interfaces (APIs). The API returns data in JavaScript Object Notation (JSON) format for users who wish to manipulate data into a customized format. For more information on the API, please see the documentation page.
