This calculator is a project of
ecliptomaniac Chris O'Byrne.
This calculator is in constant development - if you find any bugs, or
if you are getting answers that are definitely wrong, then please
let me know by email at chris (at) obyrne (dot) com - thank you! This
program is distributed under the terms of
the GNU General Public
License in the hope that it will be useful, but WITHOUT ANY
without even the implied warranty of MERCHANTABILITY or FITNESS FOR A
PARTICULAR PURPOSE. See the GNU General
Public License for more details.
the eclipses, which means that it does not depend on
any CGI script or web server to do it's work - all the calculations are
done by your computer in your browser.
The software to do the calculations is hidden within this web page -
this is, essentially, an intelligent web page!
To use this calculator while not connected to the Internet, choose
"File", "Save as..." from your browser's menu, and
save to a location on your hard drive. Then you can load the saved file
into your browser at any time by finding the
saved file on your hard drive and double-clicking it! Remember,
however, to check back here
regularly for updates to the calculator!
To find the circumstances of an eclipse, select the eclipse
and enter your location and time zone information. Then
click on the "Click here to do the calculation" button. The results
will appear in the boxes below that button.
The information given in the first 5 boxes is -
The local date and time of the event
If the event occurs while the sun is below the horizon,
an asterix (*) will appear
Alt - The altitude of the sun, in degrees, above the
Azi - The azimuth of the sun (0 = due north, 90 = due
P - The angle between the north point on the sun's disk
and the contact point with the moon
V - The "o'clock" position on the sun's face of the
contact point with the moon (eg V=12.0 means
that the contact point is in the "12 o'clock" position - ie the top of
the sun's disk)
LC - the correction (in seconds) that was applied to
the time of start or end of total or annular
eclipse due to the irregular lunar limb. Such corrections are currently
only available (courtesy Fred
Espenak, NASA/GSFC) for the 2003 May 31 annular eclipse
The information in the next 6 boxes is -
Eclipse type - the type of the eclipse as seen at your
location (taking into account that the sun may
not be above the horizon until the eclipse is in progress etc)
Duration - the duration of the total/annular eclipse.
(This box will display "n/a" if the eclipse is
partial only, or "???" if the total/annular eclipse is underway at
sunrise or sunset)
Coverage - the percentage of the sun's disk covered at
mid eclipse. (This box will display "???" if
the sun is below the horizon at mid eclipse)
Magnitude - the fraction of the sun's diameter covered
by the moon at mid eclipse
Ratio - the ratio of the apparent size of the moon to
that of the sun
(Ant)Umbral depth - the percentage of the way from the
edge of the total/annular eclipse to the centre
line that this location is at
This calculator does not account for refraction, which
makes a difference if the eclipse happens
close to sunrise or sunset
At present, corrections for the irregular lunar limb are
only available for the 2003 May 31 annular eclipse - this can make a
difference of a few seconds
to the time of the start and end of the total/annular eclipse
Also, this calculator uses eclipse elements that I
calculated myself, and they appear to differ slightly
from elements used by others. (An exception is that the elements for
2003 May 31 annular eclipse were calculated
by Fred Espenak, NASA/GSFC).
Finally, the earth rotates at a slightly irregular rate, so
it's not possible in advance to know precisely where the moon's
shadow will fall.
Fred Espenak (aka Mr.
Eclipse) and Jay Anderson - who have been
serving the eclipse-chasing community for many years with
Eclipse Bulletins. Also, Fred
has calculated all the data for the 2003 May 31 annular eclipse that
this page depends on.
Stephen McCann - who wrote the eclipse duration code
Brian Seales - the organiser behind the ecliptomaniacs
expeditions, which have provided me with much joy and many precious