Lagna - Astrological factors

Lagna (Sanskrit लग्न)
Lagna, is the degree of the Rashi (or sign) which is rising on the eastern horizon at the time of one's birth.
Lagna is the zodiac sign at the east horizon.This is more specifically called the Udaya Lagna
The Earth spins around an axis, completing one revolution in a day –causing day and night (indicating an apparent movement of Sun around the Earth) is represented as traversing once through the zodiac, i.e., covering the twelve rashis. The time spent in each rashi is referred as the duration of
lagna and the lagna is referred by the name of the rashi. At places on the equator, each day has 12 lagnas and thus each lagna will be of 2 hours (5ghatis) duration . At the poles, there are only two lagnas per day and thereforeeach lagna will be of 30 ghatis. However, the duration of lagna varies
from place to place depending on the latitude. The variation is quite large. First lagna of the day and its duration is counted from the sun rise of the day

During each soura masa, the first lagna of the day will be of the same rashi’s name as that of the soura masa. Thus during Mesha masa, the day’s first lagna will be Mesha lagna, during Vrushabha masa, it will be Vrushabha lagna, and so on. The second and subsequent lagnas of the day follow the order of the rashis.
As the Sun is moving from one rashi to the next, the first lagna duration will be of full duration at the beginning of the soura masa, on the second day the first lagna’s duration reduces by 1/30, on the 16th day the first lagna’s duration reduces to 15/30 and on the 30th day (last day) of the soura masa
reduces to 1/30 duration (giving way to the next lagna). The second and subsequent lagnas will be of full duration.
Example of Lagna duration:
During the course of each soura masa, at the equator, the duration of each lagna is 2 hours or 120 minutes. Each soura masa can be considered as of 30 days.
The first lagna keeps reducing at the rate of 4 minutes per day, i.e., from 120 minutes on 1st day to 116 minutes on 2nd day, 112 minutes on 3rd day, . .. , 4 minutes on the last day of the month.
At the same place, 2nd, 3rd, . . . 12th lagnas will be of 120 minutes on all days of the masa.
From the second day of the masa onwards the last lagna of the day (just before the next sun rise) will have the same lagna as the first but with the balance duration. Thus on 2nd day it will be of 4 minutes, on the 3rd day 8 minutes, . . and 116 minutes on the last day.



Muhurthas – Lagnas
Muhurthas are time intervals chosen for auspicious events. These are chosen by the learned, considering various factors. These Muhurthas are given names like Mesha lagna, Vrushabha lagna etc.. Further, the time is also specified by astrologers. This time specified as muhurtha will be shorter
than the lagna based on Nakshatra tyajya,

Lagna tyajya and other astrological factors.

Lagna Tyajya: One third of the lagna duration is tyajya, meaning to be discarded. It is the first one third in case of Mesha, Vrushabha, Kanya and Dhanus lagnas, second one third in case of Mithuna, Simha, Thula and Kumbha lagnas, last one third in case of Karkataka, Vrushchika, Makara
and Meena lagnas. Pushkaramsha: Sometimes lagnas of one minute duration is chosen.

This is practiced widely in North India. The best time within a lagna period is called Pushkaramsha.
Masa Tyajya: Some specified days in each of the soura masas is taboo for auspicious events.

Masa Tyajya	Pushkaramsha	Masa Tyajya	Pushkaramsha
Rashi	Days (Ghati-Vighati )	Rashi	Days (Ghati-Vighati)
Mesha	6,15 (3-01)	Tula	6, 20 ( 3-59)
Vrishabha	7, 16, 17 (2-13 )	Vrishchika	1, 10, 17 (1-06)
Mithuna	1, 6 (4-12 )	Dhanus	6, 9, 11 (3-35)
Karkataka	2, 10, 20 (1-05)	Makara	1, 2, 3, 11, 17 (2-06)
Simha	2, 16, 18 (3-23 )	Kumbha	15, 16, 17 (3-01)
Kanya	16, 29 (2-10)	Meena	6, 15, 19  (0-19)