Special Ascendants
Astronomically derived Ascendants
In Vedic Astrology, Sunrise is considered as the start of the day. The time from Sunrise to the time of birth is called Ishta kala. At the time of Sunrise, the Sun sign is rising, and within the time span of Ishta kala, the zodiac keeps rising continuously. At the time of birth, that sign is rising which we normally refer to as the Ascendant, or Lagna.
There are three other methods of arriving at a Lagna. The Bhava Lagna is calculated by not observing the actual physical rising of the signs, but taking a fixed amount of time, 2 hours, as the time it takes for a sign to rise. For every hour of Ishta kala, 15 degrees are added to the Sun’s position at Sun rise.
The Hora Lagna is based on the same technique as the Bhava Lagna, but the rate or progressing the Lagna is twice as fast: one sign per hour.
The Ghatika Lagna is also similar, but here the Lagna is progressed at a rate of one sign per 24 minutes (2 signs per hour).
In either of these Lagnas, a chart can be made using that Lagna as the first house, and placing the Grahas in the same Rashi positions as would normally be.
Other special Ascendants
Arudha Lagna is the Lagna obtained by counting as many places from the Ascendant lord, as the lord is placed from the Ascendant. There is a special rule for when the Lord of the 1st is in the 4th or 7th, in which cases the 4th house becomes the Arudha Lagna. There is also a special case for when the Lord of the 1st is in the 1st , in which case the 10th house becomes Arudha Lagna.
The chart as counted from the Arudha Lagna is mainly used for making predictions for finances, health and other worldly matters.
The Karakamsha is the sign in the Navamsha where the Atmakaraka is placed in. This sign can be used as Lagna, according to some in the Navamsha itself, and according to others in the Birthchart.
Hora Lagna
Indu Lagna