(We have fixed a bag on the Julian date of the leap
year between 1584 and 1752.)
This program offers a traditional Indian calendar based mainly on the
The Suuryasiddhaanta has a long history. The `original' version is quoted
in Varaahamihira's Pancasiddhaantikaa in the mid-6th century. (See
Neugebaur-Pingree's translation, Kopenhagen 1970.) The so-called `modern'
Suuryasiddhaanta was most popular and influential all over India after
about the 10th century. This text, together with the English translation
by E. Burgess in 1860 (Journal of the American Oriental Society), has been
a good starting point for the students of Indian astronomy. The
astronomical constants in the two texts are slightly different. We can
distingush the different sets of constants by the option B (with
biiija or without biija) in the setting. For the time after AD 1000, the
option with bija will fit better.
The later Suuryasiddhhaanta (as well
as the Aryabhatiiya) had a strange theory that the size of epicycles
slightly changes according as they are in the odd quadrants or in the even
quadrants of the deferent. In this programs, however, following the easier
method of karaNa texts, we used the mean size of the epicycles, thinking
that this would not yield significant difference. Although the planetary
positions are expressed to the unit of seconds, such accuacy should not be
In traditional Indian calendar civil
days in a half month are named by the current tithi at sunrise. We have
given the fraction of tithi at sunrise in the verbose menu so that we can
guess the possibility of different dates.
The default time of this program is
set to the local time in Ujjain, the ancient center of astronomy, which
played the role of Greenwich in the history of Indian calendar. The
latitude of Ujjian is 23.2 degrees north and its longitude is 75.8 degrees
east from Greenwich. In order to get the sunrise time of any intended
locality, you need the latitude and longitude of the place. The difference
in latitude can not be neglected, especially near the two solstices. The
local latitude can be entered with the optional menu L in the first
setting mode. The difference in longitude can slightly affect the time of
conjunction and thus it can be one of the causes of one day difference of
the date. From this version we added the option O , where the
geographical longitude can be entered. Since, however, we do not know to
what extent the longitudinal difference of the places (dezaantara) was
taken into account in ancient calendar, we can proceed with the default
In this version we offer the following three menus.
T: to find the modern date from the given
You can choose Saka samvat or Vikrama samvat. Sometimes you should take
care whether a given year is expired (atiita) or current (vartamaana).
Expired years are more common. Note that in the Indian Calendar
Sewell-Dikshit used current years.
You should also take care whether
the naming system is amaanta or puurNimaanta (see below).
The result of this menu is not
always correct. (Sometimes difference is one month because of the
occurrence of adhimaasa (intercalary month) and, very rarely, ksayamaasa
(omitted month). Thus the date can be shifted forward or backward by one
month depending on the constant numbers which were used by calendar
makers. You should confirm the result of this menu by the next menu L.
L: to find the Indian date (in amaanta) from
the given modern date in a tabular form. The result is considerably
reliable: the occurrences of intercalary months almost always agree with
those listed in Sewell-Dikshit's Indian Calendar; only the
difference of 1 day (or tithi) is to be admitted because of the different
distribution of ksayadina (`omitted day') and/or adhidina (`additional
V: to get the further items of the pancanga
(`five elements') day by day. We have added the date in the traditional
solar calendar. There are regional varieties concerning the beginning of a
solar month. Our method is this: When a samkraanti (sun's entry in a new
nirayana zodiacal sign) takes place before the midnight of a day, the
first day of the solar month is on that day. When it takes place after the
midnight, the first day of the solar month falls on the next day. For the
sake of convenience we have shown the date and time of samkraanti.
The ayanaamsa (difference of
nir-ayaNa longitude and sa-ayana longitude due to the precession of
equinoxes) is shown in this menu. According to the Suuryasiddhaanta the
rate of precession is 54 seconds per year and the difference of the two
longitudes was zero in A.D. 499. The modern value is about 50.29 seconds
per year. This means that the ayanaamsa of this program is slightly
different from that computed by the modern method.
We are not always consistent in
Romanizing Sanskrit words. The Sanskrit names of Jovian year, yoga and
karaNa are expressed in the Kyoto-Harvard transliteration system for
network communication. Those who are not familiar with this sytem is
adviced to see the table of the
NOTICE: Remember that there are two different
systems of naming the month, i.e. amaanta (`new moon ending') and
puurnimaanta (`full moon ending'). In the bright half month (sukla-paksa)
nothing is different, but in the dark half month (krsna-paksa), the
puurnimanta month name is ahead of the amaanta month name by one.
In this program the beginning of the Indian year is set for Caitra month
One can use this program for the
B.C. years with negative numbers, for example, -57 = B.C. 58. But do not
forget that the text on which this program is based belongs to the time
after about A.D. 500.
From this version we have added the Julian date for the period from
October 15, 1582 to September 13, 1752 in the menus list and verbose.
The copyright of this program belongs to the two authors. One can use this
for the purpose of dating manuscripts, inscriptions etc. easily with a
certain degrees of reliability. But we are not responsibile for any
incovenience which might be caused by using this program. Suggestions for
improvements are welcome.
If you have any questions, please contact:
M.YANO (for Indian astronomy): firstname.lastname@example.org
M.FUSHIMI (for programming): email@example.com
This version was made possible by the Grant in Aid
of the Ministry of Education, Science, Sports and Culture of the Japanese