The Picture shows the movement of sun in various zodiacal signs. While the sun moves around the zodiac, The moon goes thru 30 phases in a 30 day cycle. (Click on image to enlarge it, And In IE click on Square button on right bottom of the image to enlage it further)
The zodiac is is divided into visibly 27 parts by moon called nakshatras. As Moon takes about 27.31 days to go around the zodiac. The zodiac is also divided in 12 parts by Sun. The 27 Nakshatra's and 12 Signs are shown in the above diagram
This leads to 2 forms of month measurements.
1. Lunar Month: This is based on the Moon phases. The Sun stays in a sign for approximately 30.xx days In those 30 days. A Full moon occurs in the opposite side of the sun sign sign. The nakshatra where the full moon occurs is the names of Lunar Months. The Names of Lunar months are shown in the image.
2. Solar Month: The Sun stays in about 30.xx days in signs and takes about 365.2425 days to go around the zodiac. The Solar month is named after the 12 Signs where the Sun can be.
For example Sun can be in Libra/Tula sign from October 17th to November 15th. So this month can be called as "Tula maasa" or "Libra Month" when you want to mention the month by Sun. Or Since the full moon can now occur somwhere in Ashwini nakshatra the month is called "Aswini Maasa" or "Ashwayuja" meaning Ashwa+yuja = Conjoined Ashwa(Ashwini).
Laksmi's New Year (Lunar Year): New Moon in Libra, When Sita (Lakshmi comes back to Ayodya). The last day in Ashwini month is the Amavasya, New moon in Libra. The first phase after the Aswini Amavasya (Ashwini Krishna 15) is called Karthika maasa. Karthika first phase is Laxmi's new year.
The dark phases (Waning Phases) of the moon are called as Krishna Paksha, there are 15 of them. You can call them Krishna Paksha 1 to 15(Amavasya/New Moon). You can denote them by K1, K2, K3 to K15. Where K is for Krishna meaning Dark phase.
Similarly the Waxing Phases are called Shukla Paksha. There are again 15 of them, Shukla 1 to Shukla 15(Full Moon). They can be denoted as S1 to S15.
The Ashiwini Month's last Dark phase days from 13 to 15 are celebrated as Diwali.
Ashwini K13, Dhana Trayodhashi(meaning 13).
Ashwini K14, Naraka Chatudashi(meaning 14).
Ashwini K15, Amavasya Diwali.
The first moon phase day in Karthika month i.e. Karthika S1 is Laksmi's New Year. This is the day Lakshmi (Sita) Returns back to Ayodhya and signifies the coming of Laksmi to Home.
Other New Years are
- Makara Sankranti (Solar Year), When Sun enters Capricorn/Makara. Also called Pongal. Comes around January 14. Commences a Kali Yuga Year.
- Chaitra New Year (Lunar Year), The Amavasya in Pisces. Used as New Year for Non Financial Purposes. Chaitra S1 month. (S1 phase Before April 14th ). Vishnu's Lunar New Year.
- Mesha Sankranti Mesha New Year, (Solar Year). Sun enters Aries. mostly occurs on April 14. Indicates Sun's New Year. Also called as samvatsara year.
Wish you all a very Happy Diwali and New Year.
With Best Wishes