The
nirayana
system
is a traditional Indian system of
calendrical
computations in which the phenomenon of
precession of equinoxes
is not taken into consideration.
[1]
In Indian astronomy, the precession of equinoxes is called
ayana-calana
which literally means shifting of the solstices and so
nirayana
is
nir- + ayana
meaning without
ayana
.
[2]
Ayanacalana
refers to the continuous backward movement of the point of intersection of the ecliptic (which is a fixed circle) and the celestial equator (which keeps on moving backward). In contrast, the Indian systems of calendrical computations which take into consideration the effects of precession of equinoxes are called
sayana
systems.
Nirayana
year
[
edit
]
The
nirayana
year is the
sidereal year
, that is, is the actual time required for the Earth to revolve once around the Sun with respect to a fixed point on the ecliptic, and its duration is approximately 365.256363 days (365 days 6 hours 9 minutes 10 seconds). In the
nirayana
system, this fixed point is taken as that point 180° from the bright star
Citr?
(Spica). The starting point of the
nirayana
year coincided with the
March equinox
in the year 285 CE. Since the stars are fixed with respect to the ecliptic, the starting point remains unchanged, hence the name
nirayana
.
[3]
[4]
Duration of the
nirayana
months and year.
[5]
a
Month
|
per
?rya-Sinddh?nta
|
per
S?rya-Siddh?nta
|
days
|
gh
|
pa
|
vp
|
days
|
hr
|
min
|
sec
|
days
|
gh
|
pa
|
vp
|
days
|
hr
|
min
|
sec
|
vai??kha
|
30
|
55
|
30
|
0
|
30
|
22
|
12
|
0
|
30
|
56
|
7
|
0
|
30
|
22
|
26
|
48
|
jyai??ha
|
31
|
24
|
4
|
0
|
31
|
09
|
37
|
36
|
31
|
25
|
13
|
0
|
31
|
10
|
05
|
12
|
????ha
|
31
|
36
|
26
|
0
|
31
|
14
|
34
|
24
|
31
|
38
|
41
|
0
|
31
|
15
|
28
|
24
|
?r?va?a
|
31
|
28
|
4
|
0
|
31
|
11
|
13
|
36
|
31
|
28
|
31
|
0
|
31
|
11
|
24
|
24
|
bh?drapada
|
31
|
2
|
5
|
0
|
31
|
00
|
50
|
0
|
31
|
1
|
7
|
0
|
31
|
00
|
26
|
48
|
??vina
|
30
|
27
|
24
|
0
|
30
|
10
|
57
|
36
|
30
|
26
|
29
|
0
|
30
|
10
|
35
|
36
|
k?rttika
|
29
|
54
|
12
|
0
|
29
|
21
|
40
|
48
|
29
|
53
|
36
|
0
|
29
|
21
|
26
|
24
|
m?rga??r?a
|
29
|
30
|
31
|
0
|
29
|
12
|
12
|
24
|
29
|
29
|
25
|
0
|
29
|
11
|
46
|
0
|
pau?a
|
29
|
21
|
2
|
0
|
29
|
08
|
24
|
48
|
29
|
19
|
4
|
0
|
29
|
07
|
37
|
36
|
m?gha
|
29
|
27
|
24
|
0
|
29
|
10
|
57
|
36
|
29
|
26
|
53
|
0
|
29
|
10
|
45
|
12
|
phalguna
|
29
|
48
|
30
|
0
|
29
|
19
|
24
|
0
|
29
|
49
|
18
|
0
|
29
|
19
|
43
|
12
|
caitra
|
30
|
20
|
19
|
15
|
30
|
08
|
07
|
42
|
30
|
21
|
12
|
31.4
|
30
|
08
|
29
|
0.56
|
year
|
365
|
15
|
31
|
15
|
365
|
06
|
12
|
30
|
365
|
15
|
31
|
31.4
|
365
|
06
|
12
|
36.56
|
^a
The abbreviations
gh
,
pa
, and
vp
stand for
gha?ik?
(24 minutes),
pala
(also called
vighatik?,
24 seconds), and
vipala
(0.4 seconds).
|
Months
[
edit
]
In the calendars that follow the
nirayana
system, a month is an artificial unit of time. In the
nirayana
system, the ecliptic is divided into 12 parts of 30° and each part is called a
r??i
. The first
r??i
starts from the same point as that of the start the
nirayana
year. The beginning of a
nirayana
month is the moment at which the Sun enter into a
r??i
. The length of a
nirayana
month is the duration of time taken by the Sun to travel completely in a
r??i
, that is, to travel 30° of its elliptical orbit.
[4]
Since the speed at which the Sun is traversing its elliptical orbit around the sun is not constant, the durations of the sidereal months are also not constant. The mean length of a
nirayana
month is about 30.4369 days, but its actual length can vary from 29.45 days to 31.45 days. Calendar makers of different regions of India follow different computational systems, so, the duration of a
nirayana
month may vary from region to region.
[6]
Since the
nirayana
months are defined artificially, there are no astronomical phenomena associated with the beginning of a
nirayana
month. The exact moment at which a new
nirayana
month begins can occur at any time of day, early morning, evening or night. To facilitate dating of days, the first day of a month has to be properly defined in terms of
sa?kr?nti
, the time at which the Sun enters a new
r??i
. Unfortunately, there is no consensus among calendar-makers, and tradition varies from region to region. A few of these are:
[4]
- The Orissa rule
: The month begins on the same day as the
sa?kr?nti
.
- The Tamil rule
: The month begins on the same day as the
sa?kr?nti
if the
sa?kr?nti
falls before sunset. Otherwise the month begins on the following day.
- The Kerala rule
: The month begins on the same day as the
sa?kr?nti
if the
sa?kr?nti
occurs before
aparahna
. Otherwise the month starts on the following day. (Aparahna is the time at 3/5th duration of the period from sunrise to sunset. For example, if the times of sunrise and sunset are 6am and 6pm, the aparahna is [(3/5) x (18 ? 6) + 6]am = 1.12pm.)
- The Bengal rule
: When
sa?kr?nti
takes place between sunrise and midnight on that day, the month begins on the following day. If it occurs between midnight and sunrise, the month begins on the third day. (In some special circumstances, there are some deviations from this rule.)
Major deficiency
[
edit
]
The most important deficiency of the
nirayana
calendar is that the predictions of the dates of the onsets of the various seasons as per the
nirayana
system do not correspond to the actual dates on which they occur. This is because the seasons depend on the position of the sun on the
ecliptic
relative to the
celestial equator
. In particular, they depend on the positions of the equinoxes. Since, the positions of the equinoxes are slowly moving, the predictions of the seasons which ignore this movement of the equinoxes will be definitely erroneous.
To be more specific, the winter season begins on the
winter solstice
day which date is marked by sun's entry into
Makara
constellation. This event occurs on the 22nd December. But in the
nirayana system
, this happens not on the 22nd December but on the 14th January and the winter season is also supposed to begin on that date. Similar is the case with other seasons also. The result is that there is a clear difference of 23 days in the reckoning of seasons.
[1]
References
[
edit
]
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[
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