No 9, 4th Street, Kalyannagar, Tambaram West, Chennai 600 045, INDIA
Telefax : +91 44 2226 1742, Cell : +91 98403 69677, Email : prohithar@gmail.com
பிரதேச கிரஹண விபர அவதானம்
Javascript Eclipse Calculator
Instructions
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
