सिद्धान्तशिरोमणि: गणिताध्याय (भास्कराचार्य - ग्रहगणित, मध्यमाधिकार व स्पष्टाधिकार सटीक)

197
equal and similarly those of Meṣa and Kanyā. It will
be noted that the equatorial risings alone are equal in the
above cases but not at any other place, for in a place with
some latitude when a point like B (fig. 26) comes to the
horizon, the foot of its declination circle namely b will
not be on the horizon and there arises the chara in bet-
ween, which has to be taken into account, and be subtract-
ed from or added to the equatorial rising time as the case
may be.
Now regarding the chara-khanda of Karkaṭa it is
again 56; why it should be so is not proved by Bhāskara
but merely stated, nor any commentator took the pains to
prove. It can be proved as follows. Let in fig. 26,
δ₁, δ₂, δ₃ be the declinations at the ends of Vṛṣabha,
Mithuna and Karkaṭaka respectively. We know δ₁ = δ₃.
The chara-segments for Mithuna and Karkaṭaka i.e. when
Mithuna and Karkaṭaka are rising are to be proved to be
equal, here 56 asus. Their expressions are tan ϕ tan δ₂ −
tan ϕ tan δ₁ and tan ϕ tan δ₃ − tan ϕ tan δ₂ i.e. tan ϕ
(tan δ₂ − tan δ₁) and tan ϕ (tan δ₃ − tan δ₂). Since
δ₁ = δ₃ we perceive that they are equal but of opposite
signs. So Bhāskara says rightly “अपचीयमानत्वात् धनम्”
i.e. because of negative sign, the chara-segment of Karka-
taka while being subtracted will be rendered positive’.
Hence the rising times of Karkaṭaka, Simha and Kanya
will be respectively 1937+56, 1793+134, 1670+168 asus
or 1993, 1927, 1838 asus or 332, 321, 306 Vinadis or
5-32, 5-21 and 5-6 nadis. Thus, in as much as the rising
times of Meṣa to Kanyā are 1670−168, 1793−134,
1937−56, 1937+56, 1793+134, 1670+168 their total
is 30 nadis as should be expected because the equator
bisects the ecliptic between ♈ and ♎ and the equatorial
interval between ♈ and ♎ is 30 nadis. It will be noted
that while the equatorial rising times of Meṣa to Kanyā
are symmetrical as 1670, 1793, 1937, 1937, 1793, 1670,
their rising times at any other place are not like that but

198
constitute a different kind of symmetry as 1670—168,
1793—134, 1937—55, 1937＋55, 1793＋134, 1670＋168.
We have now to comment upon the statement
“तुलादितोऽमी च विलोमसंस्थाः ” which means that the rising
times from Tulā to Mīna are in the reverse order i.e. the
rising time of Tulā equals that of Kanyā; that of Vris-
chika equals that of Simha and so on the rising time of
Mīna equalling that of Meṣa. Thus the rising times of
Tulā to Mīna being in the reverse order are 1670＋168,
1793＋134, 1937＋55, 1937—55, 1793—134, 1670—168
for the aforesaid locality. Why it should be so can be
easily seen from the fact that Kanyā and Tulā are sym-
metric with respect to the line ♈ ♎ which bisects the
ecliptic (Ref. fig. 27). Or again we can see this in another
Fig. 27
way; the chara-segments are successively (tan ϕ tan δ₁ —
tan ϕ tan 0), (tan ϕ tan δ₂—tan ϕ tan δ₁), (tan ϕ tan ω—
tan ϕ tan δ₂), (tan ϕ tan δ₂—tan ϕ tan ω), tan ϕ tan δ₁—
tan ϕ tan δ₂ (tan ϕ tan 0—tan ϕ tan δ₁), (tan ϕ tan δ₁—
tan ϕ tan 0), (tan ϕ tan δ₂—tan ϕ tan δ₁), (tan ϕ tan ω—
tan ϕ tan δ₂), (tan ϕ tan δ₂—tan ϕ tan ω) (tan ϕ tan δ₁—
tan ϕ tan δ₂), (tan ϕ tan 0—tan ϕ tan δ₁) where δ₁ =
declination of 30°, and δ₂ that of 60°. These are there
as found before 56, 134, 168, —168, —134, —56 upto Kanyā.
But the remaining, though apparently are 56, 134, 168,
—168, —134, —56 must be taken with a reverse sign because
the rising point of the ecliptic will be to the south of the
east point and δ will be negative from 180° to 360° longi-
tude. Hence the chara Segments are 56, 134, 168, —168,
—134, —56, —56, —134, --168, 168, 134, 56 so that from
Tulā onwards they are in the reverse order as Bhāskara

100
has stated. Bhāskara's statement yet has another mean-
ing. The ecliptic from 180° to 360 being in the reverse
as can be seen in fig. 27, the time by which a particular
Rāsi rises, is equal to the time by which its seventh Rāsi
or diametrically opposite Rāsi sets. It is important to
note that the rising time of a particular Rāsi is not equal
to its setting time as can be gauged from the rising times,
for, then the rising times of Meṣa and Tulā must be equal
which is not the case. The word विलोमसंस्थाः has this
meaning as well, rising and setting being reverse directions.
Incidentally there is what is called a वृद्धकारिका
handed down i.e. a traditional statement which men-
tions "मीनमेषौ चतुर्नड्यः सार्धं चत्वारिगोघटौ etc." This
clearly pertains to the local rising times of the Sāyana
Rāsis at a place of latitude 17°-45' i.e. in between
Rajamundry and Vizianagaram, as in this latitude the
chara Segments in asus will be 230, 184, 73 which give
rise to such rising times.
We next find what are called Nirayana Swōdayas i.e.
the rising times for the locality of the Nirayana Rāsis i.e.
the Rāsis from the zero-point of the Hindu zodiac. We
shall obtain these magnitudes for Rajahmundry whose
latitude is 17°-2'. We shall however take it as 17°; also
we shall take the Ayanāṁsas to be 21° at present following
Varāhamihira. This is one of the contexts where the
knowledge of Ayanāṁsas is essential. The method is the
same as followed before; only, we have to find the decli-
nations, right ascensions, charas and therefrom the rising
times of arcs of magnitude 21°, 51°, 81°......351°. Sub-
tracting the preceding rising times from the following we
have successively the required rising times. We shall
give them under the following table.

200

201
In modern terms, the rising times of Rasis could be
found by solving the spherical triangle γEA (fig. 28) using
the Inner side inner angle formula namely .
[Fig. 28]
Fig. 28
cos 𝑥 ✕ cos 𝜔 = sin 𝑥 cot 𝜆 + sin 𝜔 tan 𝜙 I
sin 𝑥 cot 𝜆 − cos 𝑥 cos 𝜔 = − sin 𝜔 tan 𝜙
putting sin 𝑥 = t, this reduces to
t cot 𝜆 − √(1 − t²) cos 𝜔 = − sin 𝜔 tan 𝜙
or (t cot 𝜆 + sin 𝜔 tan 𝜙)² = (1 − t²) cos² 𝜔
∴ t² (cos² 𝜔 + cot² 𝜆) + 2t ✕ sin 𝜔 tan 𝜙 cot 𝜆 −
cos² 𝜔 = 0
∴ t =
−sin 𝜔 tan 𝜙 cos 𝜆 ± √[sin² 𝜔 tan² 𝜙 cot² 𝜆 + cos² 𝜔 (cos² 𝜔 + cos² 𝜆)]
──────────────────────────────────────────────────────────────────────────
cos² 𝜔 + cot² 𝜆
Putting successively 𝜆 = 30°, 60°...360° and ignoring
the negative sign of the radical we have the sines of rising
times of arcs of the ecliptic of 30°, 60° etc. Subtracting
26

202
the preceding from the succeeding, we have successively
the rising times. Thus the rising time of Mesha is
√3 sin² ω tan² ϕ + cos² ω (cos² ω + 3 − √3 sin ω tan ϕ II
────────────────────────────────────────────────────────
3 + cos² ω
That of Meṣa and Vṛṣabha put together, the rising
time is .
√sin² ω tan² ϕ + 3 cos² ω (cos² ω + ⅓) − sin ω tan ϕ III
───────────────────────────────────────────────────
√3 (cos² ω + ⅓)
The combined rising time of the 3 Rasis Meṣa, Vṛṣa-
bha and Mithuna is from I using tables cos⁻¹ (tan ω tan ϕ)
= 5046 asus which exactly accords with what we have
found previously namely 1505+1659+1882 = 5046. Also
putting in I λ = 180°, we have sin x = 0 or x = 180° =
10800 asus ; subtracting 5046, we have the combined times
of rising of Karkataka, Simha ahd Kavya to be 5754 asus
as we have had. Putting again λ = 270, we have cos°⁻¹
(tan ω tan ϕ) = 2π − 5046 whioh signifies that the sum
of the rising times of the last three rasis is the same as
that of the first three which again means that the sum of
the rising times of Tula to Dhanus is equal to the sum of
the rising times of Karkaṭaka, Simha and Kanya establish-
ing Bhaskara's statement “विलोमसंस्थाः”.
Verse 60. Computations of Lagna, Udayāntara and
the like from the rising times of big arcs of the ecliptic
like Rasis will be approximate, whereas one desirous of
greater approximation has to find the same from the
rising times of smaller arcs likes Horas and Dṛkkāṇas, so
as to be more correct.
Comm. Rasis divided into halves are called horas
and if divided into one-third parts are called
Dṛkkāṇas. The meaning of the verse is that if after
having found the rising time of a particular Rāśi say
Meṣa, we say that one-third of that rising time is that of
one-third of that Rāśi, we will be making only an appro-

203
ximate statement just like saying that ‘Since 12 Rasis
rise in the course of a sidereal day, so each rasi rises in
1800 asus’ which is far from truth being based on a crude
rule of three. So, Bhāskara says, Acharyas like Aryabhata
insisted on finding the rising times of Dṛkkāṇas, in as
much, as while computing the Lagna or the point of inter-
section of the Ecliptic with the horizon, we will be nearer
the truth by using the rising times of smaller arcs like
Dṛkkāṇas than broadly using those of Rasis.
Verse 61. Bhujāntara correction.
The equation of centre of the Sun multiplied by the
equatorial rising time of the Rāsi occupied by the Sun,
and divided by 1800, and then again multiplied by the
true daily motion of a planet and divided by the number
of asus in a day, is the correction in the planet positive
or negative according as the equation of centre of the Sun
is positive or negative.
Comm. This Bhujāntara correction arising out of
the Sun’s equation of centre is prescribed even for the Sun,
as well as for the other planets. The planets are originally
computed for the rising time of the Mean Sun, whereas
we are interested to know the positions at the True Sun-
rise. The position of the Sun also is originally computed
for his mean rise and is therefore to be rectified to get his
position at his true rise. So even the Sun is not exempt
from the correction. It will be noted here that as the
equation of centre pertains to the eccentricity of the Sun’s
orbit, this correction of Bhujāntara is a correction for the
so-called modern ‘Equation of time due to eccentricity’.
In other words, the Sun’s equation of centre converted
into time is exactly what is called the Equation of time
due to eccentricity.
The formula prescribed for the correction is as follows.
Suppose the Sun is in a particular Rāsi which rises at the
equator in x asus. Let the equation of centre of the Sun be

204
E minutes of arc. Then the equatorial rising time of E is
(E × x) / 1800 asus because there are 1800' in a Rasi. We have to
provide a correction in the planetary position including that
of the Sun for this time. If the planet goes Y' during
21659 asus of a day, what arc is covered by the planet or
the Sun in (E × x) / 1800 asus? The result is (E × x) / 1800 × y / 21659
minutes of arc. This correction is positive if the equation
of centre of the Sun is positive, for, we want the planetary
position for a latter time than Mean Sunrise, since the
positive equation of centre advances the True Sun over
the Mean. This correction will be appreciable only in the
case of the Moon having a rapid motion.
Verses 62, 63. The correction known as Udayāntara.
The difference in minutes of arc in the longitude of
the Sāyana mean Sun and the asus in his Right ascension,
multiplied by the daily motion of the planet and divided
by 21659 is the result to be added to or subtracted from
the planet's longitude according as the asus in the Sun's
Right ascension are greater or less than the minutes of arc
of his longitude. This is what is called Udayāntara
correction in the planetary position.
Comm. (1) We have seen that the Bhujāntara is a
correction in the mean planetary position due to the
Equation of time in Eccentricity.
(2) This Udayāntara is a correction in the same
due to the Equation of time in obliquity.
(3) Some have misconstrued that this Udayāntara
correction is the Equation of time in the obliquity itself,
whereas it is a correction to be effected in the planetary
position due to the Equation of time due to obliquity.

205
(4) The maximum equation of centre in the Sun
has a magnitude = 13 2°/3 × 1/2π = 41/3 × 7/44 = 287/132 = 2° — 10'
Converting this into time at the rate of 15° per hour
(since in one hour diurnal rotation of the earth is equal to
15°) we have 13/6 × 4 minutes = 26/3 = 8'—40''. The maxi-
mum equation of centre according to modern astronomy
is 2e expressed in radiaus where e = 1/60 (.0167339) = 2 × 1/60
radiaus = 2 × 1/60 × (180 × 7)/22 degrees = 21°/11 = 1°—54' — 33'.
As such the max. Equation of time due to eccentricity is
21/11 × 4' = 84'/11 = 7'—38''. The small difference in the
two values arises out of the difference in the max. equ-
ations of centre. Any way it is clear that, in as much as
the Bhujāntara correction is necessitated on account of
the equation of centre in the Sun, to obtain the planetary
positions computed for the mean Sunrise at the time of
True Sunrise, the Bhujāntara correction is a correction in
the planetary position, on account of the equation of time
due to eccentricity. The max. correction to be effected in
even the quick moving Moon amounts to (8 × 790)/(24 × 60) = 79/18 =
4'—23.3''.
(5) We have said in the translation of the verse.
‘The asus in the Right ascention of the mean Sun’,
where what exactly is stated by Bhāskara is, the time of
rising of the small arc covered by the Sun in the particular
Sāyana Rasi in which the Mean Sun is, (भुक्तासवः) together
with the rising times of the previous Sāyana Rasis covered
by the Sun. The meaning is therefore the rising time of
an arc of the ecliptic equal to the Sāyana longitude of the
ecliptic which is measured by his Right ascension at the

rate of 15° per hour or 6° per nadi or 10 Vinādis per degree
or 60 asus per 60 minutes of arc or as many asus as there
are minutes of arc in the right ascension of the mean Sun.
So, what is stated by Bhāskara is the difference of the
minutes of arc in the mean longitude of the Sun and the
minutes of arc in his right ascension ie. (l—a) expressed
in minutes. We know that the total equation of time
arising out of unequal motion in the true longitude of the
Sun ie. ☉ in comparision with the equal motion in his
right ascension ie. a is measured by ☉—a which may be
expressed as (☉—l) + (l—a) where l is his mean longi-
tude, ☉—l = Equation of centre and so the time
expressed by ☉—l is the equation of time due to obliquity.
The difference l—a arises out of the obliquity of the
ecliptic and so the time expressed by l—a is the equation
of time due to obliquity. We have the modern formula
Cos ω = tan a / tan l so that (1 — cos ω) / (1 + cos ω) = (tan a — tan l) / (tan a + tan l) =
(sin a — l) / (sin a + l)
∴ Sin (a — l) = tan² ω/2 sin (a + l). As a is very
nearly equal to l, we could write, when expressed in
radiaus a—l = tan² ω/2 sin 2l. Thus the maximum
difference between a and l arises when 2l = 90° ie. l = 45
degrees ie. at the mid-point of the first quadrant; the mini-
mum difference is when 2l = 270 ie. l = 135 ie. at the middle
point of the 2nd quadrant. Also the numerical magnitudes
of the max. as well as the minimum value are each tan² ω/2
ie. they are equal. Since this is expressed in radiaus,
converting into time the numerical value of the max. and
minimum equation of time due to obliquity is 9.87′. Thus
we can write l—a = 9.87′ sin 2l. Again where l = 225,
2l = 450 so that l—a will have a positive max.; and again
when l = 315, 2l = 630 so that l—a will have a negative
maximum value. Also when l has values 0, 90, 180, 270 it
is zero. Thus the equation of time due to obliquity is zero
at ♈, ie. the vernal equinox; +ve in the first quadrant

. 207
increasing from zero to 45 degrees and then decreasing
from 45° to 90°; assuming the value zero at 90°, then
negative in the second quadrant negatively increasing from
zero to a maximum as l increases from 90° to 135°, and
then negatively decreasing from the maximum value to
zero at the end of the second quadrant ; again behaving in
the 3rd quadrant as in the first and in the fourth as in the
second.
(6) It was stated by Mr. Mazumdar in his introduction
to the Siddhānta S'ekhara of S'ripati published by the
Calcutta University as well as by pandit Babuaji Misra,
the editor thereof that this Udayāntara correction was
first mentioned by S'ripati, and it meant equation of time
due to obliquity. In fact S'ripati states (Verse I ch. eleven)
“ अन्त्यभ्रमेण गुणिता रविबाहुजीवाऽभीष्टभ्रमेण विहृता, फलकार्मुकेण,
बाहोः कलासु रहितास्ववशेषकं ते, यातासवो युग्मयुजोः पदयोः धनर्णम् ”
l expressed in minutes — H sin⁻¹ (H sin ☉ H cos ω / H cos δ) express-
ed in asus = what are called elapsed asus and are +ve,
+ve, +ve and —ve in the successive quadrants. We saw
before that H sin α = (H sin ☉ H cos ω / H cos δ) so that S'ripati
meant l - α, the former expressed in minutes of arc and
the latter in asus, or what is the same (l—α) both expressed
in minutes or asus. These give the gain of l over α.
Immediately after this verse S'ripati goes to a different
topic, and never mentions (as understood from the printed
text) any further details as to what is to be done with
these Yātāsus. Since Bhāskara says explicitly that for
these Yātāsus, the planets are to be corrected, we may
surmise that there should have been in S'ripati's text also
another verse detailing the usage of those asus.
(7) We shall now attend to what Bhāskara gives by
way of explanation of the verses in question, The Ahar-

208
gaṇa found by us is what is called Madhyama Sāvana-
ahargaṇa or number of days according to mean solar
reckoning, a reckoning made on the basis of taking
uniform motion of the Sun in right ascension. The
planets computed for the Sun-rise on this basis, are to be
corrected for the true Sun-rise which goes according to the
measure of ☉ ie. the true longitude of the Sun. But in
the name of Bhujāntara we have-effected the correction
for ☉ - l ; so what remains is to effect correction for l - a.
This correction is known as Udayāntara.
In other words, since we could not compute the
Sphuṭa Sāvana-ahargaṇa, when we deem that x days
have elapsed according to the mean solar reckoning from,
the epoch upto the mean Sun-rise x ± f might have
elapsed according to Sphuṭa Sāvana-ahargaṇa where f
is a fraction. A correction is to be effected for this
fraction f of a day and it is of the form ☉ - a =
☉ - l + l - a. In the beginning Bhāskara said that mean
planets are had being computed out of the mean solar
ahargaṇa, at the time when the mean Sun is about the
eastern horizon of the equator. Why did he say ‘about
the horizon’? It is because the mean solar ahargaṇa
indicates a Sun-rise on the basis of equal motion in right
ascension whereas on the basis of equal motion in l, he
would be about the horizon. Had we been able to compute
Sphuṭa-Sāvana-ahargaṇa, we could have got direct the
planetary position when the true Sun is on the horizon.
The correction for the difference in ☉ and l having been
attended to through Bhujāntara, we are now to attend to
the correction for the difference l - a.
Verse 64. Another way of looking at the same.
Had we obtained the Ahargaṇa in terms of the local
risings of the Rasis in the place of the equatorial, and
computed the planetary positions for the local true Sun-
rise obtained that way, we would have done the three

209
corrections namely Bhujāntara, Chara and the Udayāntara
as well.
Comm. The correction of chara arises out of the
difference between the equatorial risings and local risings
of the mean Sun. The local mean Sun pertaing again to
uniform motion along the celestial equator Udayāntara
has to be effected for l—a, ie. for the local mean Sun on
the ecliptic. Thus we have obtained the planetary posi-
tions for the local mean Sun-rise and to obtain them for
the True Sun-rise, Bhujāntara is to be effected.
Verse 65. An alternative method of effecting the
Udayāntara correction.
Double the H sine of the Sāyana longitude of the Sun
derived out of the smaller H sin-table, being multiplied
by the daily motion of the planet and divided by 270 and
the result in seconds of arc is to be corrected in the plane-
tary position positive or negative according as the Sun is
in the even or odd quadrants.
Comm. (1) In symbols the correction indicated is
(m H sin 2l) / 270 where m is the planet's mean daily motion in
minutes of arc, l the longitude of the mean Sun, and
H sine is taken where the radius = 120. In the commen-
tary under the verse, Bhāskara adds 'Each quadrant of
the eclipse rises (at the equator) in ¼th of a day but
each Rāśi does not rise in 1/12 of a day. Since this
Udayāntara correction vanishes when the Sun is at the
ends of quadrants it must be construed that this
correction increases positively or negatively from the
beginning of the quadrant to the middle and decreases
from the middle to the end of a quadrant. Saying that a
particular Rāśi rises at the equator in n nādikās is only
an approximate statement since the Rāśi does not rise
uniformly. That is why astronomers like Aryabhata
27

stipulated finding the risings of smaller arcs like horas and
Dṛkkāṇas. Find (H sin l × H cos ω) / (H cos δ) ie. H sin α. Take
the asus in the arc of this H sine ie. find α in minutes.
Then l - α gives the number of asus for which the correct-
ion in the planetary position is to be effected, for, by
these asus the True Sun-rise is accelerated or belated. In
the middle of a quadrant these asus will be a little above
26 Vinadis. To obtain them at any point of the quadrant,
take H sin 2l as the argument so that the maximum correct-
ion will be had at the middle of the quadrant by this
argument. Then the rule of three is ‘ If by 120 as radius,
we have 26 Vinadis, what shall we have for H sin 2l ?’
The result is (H sin 2l × 26) / 120 = (H sin 2l) / 4½ approximately.
Then another rule of three. “ If by 60 Vinadis we have
m' of the planetary motion, where the daily motion of the
planet is m°, what shall we have for (H sin 2l) / 4½ ?” The
result is (H sin 2l × m) / (60 × 4½) minutes = (H sin 2l × m) / 270 . Then
the sign of the correction is clear.
(2) We shall now prove Bhāskara’s statement that
at the middle of the quadrant, the correction is 26 Vinadis.
We saw above that l - α = tan² ω/2 H sin 2l. It is really
creditable on the part of Bhāskara to have seen by intuit-
ion that the argument is H sin 2l. The maximum
correction is therefore tan² ω/2 expressed in asus or minu-
tes of arc. Let x = tan² ω/2
log x = 2 log tan ω/2. Take ω = 24
Then log x = 2 × 1̄.3275 = 2̄.6550
∴ x = ·04519 radian = 155 minutes of arc ie.
155 asus = 155 / 6 = 26 apply.

211
(3) Taking the case of the Moon, the max correct-
ion amounts to (790 × 120) / 270 = 5' — 51''.
Verses 66, 67. The computation of Tithi, Nakṣatra
and Yoga.
The elongation of the Moon ie. the excess of the
Moon's longitude over that of the Sun in degrees. (In
case the former is smaller, add 360° to it and subtract
Sun's longitude) being divided by 12 and 6, the quotients
represent the elapsed tithis and Karaṇas. If the elapsed
Karanas are K, count K — 1 beginning from Bava to
get the current Karaṇa and count from Śakuni to get
the current one beginning from the mid-moment of
Kṛṣṇachaturdasī. Take again the planetary position or
that of the Moon in particular as well as the sum of
the longitudes of the Sun and the Moon both expressed
in minutes of arc and divided by 800. The first quotient
gives the elapsed stars ie. the Stars covered by the planet
or the Moon; whereas the second quotient gives the
elapsed Karaṇas. Then take the remainders in seconds
and divide by the respective daily motions in minutes i.e.
in the case of the planets or the Moon divide by their
respective motions and in the case of yogas divide by the
sum of the motions of the Sun and the Moon. Then the
results give the times in nādīs as to how much the next
nakṣatra or yoga have elapsed. If it be required to find
as to how long the next nakṣatra or yoga will last,
substract the remainder from 800, and divide by the daily
motions in minutes as mentioned above. The results
give as to how many nādīs beginning from the morning
concerned, the next nakṣatra or yoga will last.
Comm. (1) A lunation i.e. the time from the moment
of New Moon to the next New Moon is divided into
30 parts called Tithis. Their names are pratipat, Dwitiyā
etc. upto the 15th purnima or full Moon and again

212
pratipat, Dwitīyā etc. upto the 30th i.e. Amāvāsyā or New
Moon. Thus pratipat starts when ☾ = ☉ i.e. when the
longitude of the Moon is equal to that of the Sun i.e.
from the moment of New Moon when the Moon is in
conjunction with the Sun. अमा सह = वसतः सूर्य्याचन्द्रमसावस्या
मित्यमावस्या i.e. Amāvāsyā is that point of time when
the Sun and the Moon are together. Pratipat lasts
till ☾ = ☉ + 12°; then Dwitīyā begins and lasts till
☾ = ☉ + 24; Thus purnima begins from the moment
when ☾ = ☉ + 168 and lasts till ☾ = ☉ + 180° and
Amāvasyā begins when ☾ = ☉ + 348 and lasts till ☾ is
again equal to ☉ Thus a tithi is the time that is taken
by the Moon to overcome the Sun by 12° beginning from
the moment of New Moon. In other words the tithi is a
measure of the phase of the Moon with a particular
convention.
(2) In modern astronomy the phase of the Moon or
that of a planet is measured by the formula (1 + cos EPS) / 2
where P is the planet or the Moon. Since ES is almost
Fig. 29
parallel to PS (Fig. 29) ÊPS may be taken to be nearly
equal to P̂ES which is the elogation of the planet or the
Moon so that phase = (1 - cos EPS) / 2 approximately. So

213
in modern astronomy also the phase is measured through
the elongation. But the maximum phase in modern
astronomy is taken to be unity as could be seen from the
formula, for, when EPŜ = 180°, the phase = 1. Thus
the phase multiplied by 15 gives approximately the tithi.
We shall have occasion to deal with this topic later.
(3) Suppose ☾ − ☉ = E°. The number of the
tithis elapsed is equal to the quotient in E / 12. Take the
remainder r°. It means during the current tithi which
has a duration of 12°, r° have elapsed. Let the daily
motions of the Moon and the Sun be m and s so that the
Moon overtakes the Sun by m − s (expressed in minutes
for convenience) during 60 nādīs. The elapsed time of
the current tithi in nādīs is given by (r × 60 × 60) / (m − s). But
r × 60 × 60 = Seconds of arc of the remainder so that
it is said “गतैष्यविलिप्तिकाः”. If it be required to find how
many nādīs the next tithi lasts, (12−r)° or (12−r) × 60′
is to be gained by the Moon over the Sun. So the time in
Nādīs = ((12 − r) × 60 × 60) / (m − s) = एष्यविलिप्तिकाः / (m − s) .
(4) A lunation is again divided into 60 Karaṇas
and so 6° of increase in elongation correspond to a Karaṇa.
These Karaṇas are eleven in number, out of which 4 are
fixed to occur during the latter half of Kṛṣṇa Chautùrdasī,
during the two halves of Amāvāsyā and the first half of
the Sukla pratipat. Their names are Sakuni, Chatuṣpāt,
Nāgava, and Kimstughna. So there remain 56 halves of
tithis during the lunation during which the remaining
seven Karaṇas, Known as Bava, Bālava etc. rotate eight
times. Thus the first half of the duration of any tithi is
covered by one Karaṇa and the latter by another. The
computations of Karaṇas proceeds as with respect to tithis

214
but dividing the elongation by 6, we are asked to count
K — 1, (where K is the quotient) beginning with Bava
because the first half of Sukla pratipat is covered by the
fixed Karaṇa Kimstughna. The computation of the elapsed
as well as the remaining nādīkas of a particular Karaṇa,
it proceeds on the same lines as that of a tithi.
(5) The Nakṣatra in which a planet or the Moon
is situated is then found. The zodiac is divided into 27
equal divisions beginning with its zero point and each
division is named after the brilliant star of that division.
Those stars are Aświnī, Bharaṇī etc. The star occupied
by the Moon has a special significance in the Hindu
calendar, it being spoken of that every day is presided over
by a nakṣatra. This happens so because the Moon’s
sidereal period is approximately 27 days.
(6) To compute the Nakṣatra in which the planet
or Moon is, take its longitude in minutes of arc λ; divide
by 800, since each star division consists of 360° / 27 = (360 × 60) / 27
minutes = 800'. The quotient gives the elapsed nakṣa-
tras. To get the elapsed nādikās of the current nakṣatra
or the remaining, let the remainder be r'. Then the
proportion is ‘If during the day of 60 nādīs, the planet
or the Moon goes p minutes what time does it take to
cover r' or 800 — r'’. The answer is
(r' × 60) / p' or ((800 — r') × 60) / p' = गतैष्यविलिप्तिकाः / p' .
(7) Regarding yogas, let the longitudes of the Sun
and the Moon be ☉ and λ in minutes of arc; let their daily
motions be s and m in minutes. If the sum of the longi-
tudes is 800', we say the first yoga named Viṣkambha is
over, if the sum is 1600', the second Yoga, named prīti
has elapsed. Thus going on if the sum is 360°, we say the
27 yogas have elapsed and the first again begins. Since
the sum of the daily motions of the Sun and the Moon

215
are on the average 59'—8''+790'—35''=850', to cover
one Yoga, they take roughly one day since the duration
of a yoga is of 800'. To get the number of elapsed yogas,
divide (⊙+M)' where M is the longitude of the Moon by
(s+m). To get the elapsed nādīs which are given by the
remainder r' or the remaining nādīs of the current yoga
which are given by 800; the proportion is ‘If by s+m
gain in the sum of the longitudes we have 60 nādīs, what
time is indicated by r' or 800—r'?’. The answer is
(r' × 60)/(m + s) or ((800 — r)' × 60)/(m + s) = गतैष्यविलिप्तिकाः/(m + s) .
By the word गतैष्यविलिप्तिकाः is meant therefore the number
of seconds of arc as many as the remainder r or (800—r)
is in minutes or what is the same the remainder or 800—r
converted into seconds.
(8) The tithi, karaṇa, nakṣatra of the Moon and
yoga constitute four of the Angas of the panchānga or the
Hindu Calendar the fifth being the week-day. All these
five are supposed to have their effects good or bad on living
beings.
Verses 68, 69. The correction what is called Nata-
karma.
The Zenith distances of the Sun and the Moon at the
end of Purṇimā or Amāvāsyā at the time of lunar or solar
eclipse, being expressed in nādīs, are multiplied by 6 to get
the degrees. Let their H sine be got from the short table
of H sines. Multiply it by the equations of centre of the
Sun and the Moon. Divide by 4920, and 4361 respectively.
If the Sun be in the Eastern hemisphere, let the result
pertaining to the Sun be subtracted from his position ; if
in the Western, let it be added to his position. If the
Moon be in the Eastern hemisphere and if his equation
of centre be negative let the result be added to his position;
if the equation of centre be positive, let the result be sub-
tracted from his position in either of the hemispheres.

216
Again from these positions, let the tithi be computed and
again let the above process be carried out until a constant
time is arrived at for conjunction or opposition.
Comm. (1) The above procedure is accepted by
Bhaskara as Āgama enunciated by Brahmagupta and
reiterated by Chaturveda as giving results that accorded
with observation. We shall see that the correction known
in modern astronomy as 'correction due to astronomical
refraction' is indicated here, though it was not stated
explicitly.
In fact what was stated by Brahmagupta was that
the periphery of the Manda epicycle given as 13⅔° for the
Sun and as 31-36 for the Moon hold good only on the
meridian but the periphery of the Sun is to be increased
or decreased by 20' according as the equation of centre is
negative and the Sun is the Eastern equatorial horizon,
or western equatorial horizon. If the equation of centre
be positive the reverse correction is to be effected in
the periphery i.e. for negative equation of centre.
Periphery on the Eastern equatorial horizon = 14°-0
On the meridian = 13°-40'
On the Western equatorial horizon = 13°-20'
For positive equation of centre
Periphery on the Eastern unmandala i.e.
equatorial horizon = 13°-20'
On the meridian = 13°-40'
On the Western unmandala = 14°-0
In the case of the Moon, for negative equation of
centre.
On the Eastern unmandala = 30 - 44
On the meridian = 31 - 36
On the Western unmandala = 32 - 28