This calculator uses Javascript to do the calculations for 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 horizon
Azi - The azimuth of the sun (0 = due north, 90 = due east etc)
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
Limitations
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
(courtesy of Fred Espenak, NASA/GSFC) 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 have not been
checked - I calculated those elements myself, and they appear to differ
from elements used by others.
Finally, it is not possible to predict in advance precisely how fast the
earth will rotate.
Acknowledgements
Jean Meeus - for his excellent books Elements of Solar Eclipses
1951-2200 and Astronomical Formulae for Calculators, which provided
the algorithms for this page
Fred Espenak (aka Mr. Eclipse) and
Jay Anderson - who have
been serving the eclipse-chasing community for many years with the NASA Eclipse
Bulletins. Fred, in particular, provided the lunar limb profile data and
the eclipse elements for the 2003 May 31 annular eclipse
Stephen McCann - who wrote the eclipse duration code
Brian Seales - the organiser of the Irish 1999 Bulgaria, 2001 Madagascar
and 2002 South Africa ecliptomaniacs eclipse expeditions
which have provided me with much joy and many precious memories