Vedic Astrology: Calculation of Ascendant or Lagna


Ascendant is the point of ecliptic on the eastern horizon at a specific time.
Let us calculate the ascendant step by step
To calculate this point tropical longitude of sun is required.

Step 1: Calculate the tropical longitudes of the sun.
Tropical longitude of sun = Nirayana longitudes + Ayanamsha.
Step 2: Calculate the difference between the birth time (LMT) and a sunrise on a given day. This is called as Ishta kala.
Step 3: Consider the sign in which the sun is in and the degrees he has traversed in that sign. ( Note: Consider the tropical longitudes of the Sun. )
Step 4: Calculate by direct proportion the expired portion of the sign the sun is in at the time of sunrise.
Step 5: Calculate the unexpired portion by deducting the expired portion of the sign as calculated in the fourth step.
Step 6: The duration as calculated in the 5th step should be deducted from the Ista Kala. If duration of the sign is greater than Ista Kala then ignore this step. Since the sign itself is the rising sign ignore step 7 and go to step 8.
Step 7: Deduct the duration of each successive signs up to the sign you may not be able to deduct anymore. This will happen when the duration of the sign is greater than the remainder. This is the rising sign at the time of the birth. (The duration of the sign varies from place to place. So to determine the sign duration we have to calculate the Rasimanas as given in another post. Refer the Rasimanas for Pune and Hong Kong in Annex A)
Step 8: The remainder as calculated in step 6 or 7 * 30 degrees / the duration of the sign.
Step 9: The degrees thus determined are the tropical longitudes of the ascendant. Deduct the ayanamsha for the year and the result is the nirayan longitudes of the ascendant.
Example:
Particulars
Pune
Hong Kong



Tropical longitude of sun (A)
3/9/44/00
3/9/44/00

(2/15/51/35 + 23/52/25)
(2/15/51/35 + 23/52/25)



Birth Time - Sunrise (B) (Ista kala)
11/58/28
14/47/24



Sign of the sun (C)
Cancer
Cancer



Degrees of the sun in Cancer (D)
9 deg 44 min
9 deg 44 min



Expired portion in cancer (E)
43 min 43 sec
44 min 4 sec
(D) * (rasimanas) / 30





Un-expired portion in cancer (F)
91 min 3 sec
91 min 46 sec
(rasimanas) - (E)





Ista Kala
11/58/28
14/47/24
Less Duration of cancer
91 min 3 sec
91 min 46 sec
Balance
10/27/25
13/15/38
Less Duration of leo
2/14/10
2/16/43
Balance
8/13/15
10/58/55
Less Duration of Virgo
2/9/41
2/12/52
Balance
6/3/34
8/46/03
Less Duration of Libra
2/9/41
2/12/52
Balance
3/53/53
6/33/11
Less Duration of Scorpio
2/14/10
2/16/43
Balance
1/39/43
4/16/28
Less Duration of Sagittarius
2/14/46
2/15/50
Balance
*
2/00/38
Less Duration of Capricorn

2/1/38
Balance

*
*Now we are in a situation where we cannot deduct the rasimanas from the ista kala. This indicates the tropical sign rising at the horizon. Thus tropical Sagittarius is rising in Pune while tropical Capricorn is rising in Hong Kong.
Tropical sign rising
Sagittarius
Capricorn
Duration of the sign
2/14/46
2/1/38
Balance left
1/39/43
4/16/28
(Balance) * 30 / (2/14/46)
22/11/51
29/45/12



Less Ayanamsa on July 1, 2001
23/52/25
23/52/25



Nirayana rising sign is
Scorpio
Capricorn
Longitudes in the sign
28/19/26
5/52/47
Note : It may be noted that the correct ascendant at Pune as per modern trigonometric calculation is 29 deg 46 mins of Scorpio instead of 28/19/26. Similarly the correct ascendant at Hong Kong as per modern trigonometric calculation is 6/42/00 of Capricorn instead of 5/52/47. The difference can be safely ignored at this stage.

Annex A







Sr.no
Sign
Rising period
+/-
Charakhandas at 18N32
Charakhandas at 22N20
Rasimanas or duration

Rasimanas or duration


at 0 Lat.



of signs at 18N32

of signs at 18N32
1
Aries
111 min. 36 sec
-
18 minutes 5 seconds
21 minutes 16 seconds
93 minutes 05 seconds

90 minutes 20 seconds
2
Taurus
119 min 40 sec
-
14 minutes 30 seconds
17 minutes 3 seconds
105 minutes 10 seconds

102 minutes 37 seconds
3
Gemini
128 min 44 sec
-
6 minutes 2 seconds
7 minutes 6 seconds
122 minutes 42 seconds

121 minutes 38 seconds
4
Cancer
128 min 44 sec
+
6 minutes 2 seconds
7 minutes 6 seconds
134 minutes 46 seconds

135 minutes 50 seconds
5
Leo
119 min 40 sec
+
14 minutes 30 seconds
17 minutes 3 seconds
134 minutes 10 seconds

136 minutes 43 seconds
6
Virgo
111 min. 36 sec
+
18 minutes 5 seconds
21 minutes 16 seconds
129 minutes 41 seconds

132 minutes 52 seconds
7
Libra
111 min. 36 sec
+
18 minutes 5 seconds
21 minutes 16 seconds
129 minutes 41 seconds

132 minutes 52 seconds
8
Scorpio
119 min 40 sec
+
14 minutes 30 seconds
17 minutes 3 seconds
134 minutes 10 seconds

136 minutes 43 seconds
9
Sagittarius
128 min 44 sec
+
6 minutes 2 seconds
7 minutes 6 seconds
134 minutes 46 seconds

135 minutes 50 seconds
10
Capricorn
128 min 44 sec
-
6 minutes 2 seconds
7 minutes 6 seconds
122 minutes 42 seconds

121 minutes 38 seconds
11
Aquarius
119 min 40 sec
-
14 minutes 30 seconds
17 minutes 3 seconds
105 minutes 10 seconds

102 minutes 37 seconds
12
Pisces
111 min. 36 sec
-
18 minutes 5 seconds
21 minutes 16 seconds
93 minutes 05 seconds

90 minutes 20 seconds


Activity: Calculate the position of ascendant at Singapore on 1 st July 2001 18:00(IST) also calculate sunrise and sunset of Singapore on the same day.



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