Ayana is known in Jyotish Veda as a period of time during a year when Surya (the Sun) moves to a certain direction passing certain Rashi.
From the moment of touching the tropic1 of Makara (Capricorn) (so-called tropical Makara Sankranti), Surya moves northward till it reaches the tropic of Karkata (Cancer). During its northward movement, which is also called as Uttara Ayana, Surya passes through the signs of:
- Makara (Capricorn),
- Kumbha (Aquarius),
- Meena (Pisces),
- Mesha (Aries),
- Vrshabha (Taurus)
- and Mithuna (Gemini).
This period in Vedic tradition
is considered to be auspicious, as it's known as "Deva Day", and all
events taking place at this time, are under supervision of Devas (Gods).
So it is believed that this period is auspicious for holding such big
events as marriage, moving into a new house and so on.
Similarly, from the moment of touching the tropic of Karkata (Cancer) (so-called tropical Karkata Sankranti), Surya (the Sun) begins its southward journey, known as Dakshina Ayana, till it reaches the tropic of Makara (Capricorn). During its southward movement, Surya passes through the signs of
- Karkata (Cancer),
- Simha (Leo),
- Kanya (Virgo),
- Tula (Libra),
- Vrshchika (Scorpio)
- and Dhanu (Sagittarius).
This period in Vedic tradition is inauspicious, and is known as "a night
of Devas" when all events taking place at this period of time are under
the supervision of the Asuras (demons).
1 - NB!: it is extremely important that tropical zodiac (not the sidereal one) is used for the calculation of Ayana (this method of Ayana calculation is also used for our Favorability Graph). It is a fundamental principle that is supported by many classical sources (for example, Jyotirvidyabharnam) as well as various Acharyas and sages (such as Narada and etc). And it's quite logical: when you use sidereal zodiac (and the ever-increasing value of Ayanamsha along with it) the beginning of each Ayana will be moved further and further away from the real one. If we take Surya's entrance into Makara (Capricorn) using current Ayanamsha (i.e. sidereal zodiac) it will happen in the middle of January. But if we take one without Ayanamsha (i.e. tropical zodiac) then it'll be the 22nd or the 23rd of December. More than that, 6 Ritu (6 seasons) calculation is based on Ayanas. As Ayanamsha's value will increase through the time, the usage of sidereal zodiac will cause an effect when, for example, the calculated beginning of the winter season Shishir will start in time when Gresham (summer season) is already in full swing.
