Lunisolar Hindu Calendar

 In the previous video, we explored events associated with the movement of Sun, Earth and Moon. 

Let us understand how months of the Hindu Calendar are decided with the help of this model.  Though Hindu Calendar is based on the cycles of the Moon, it tries to accommodate solar year as well in single framework. This is done by adding 'Adhik Maas' or extra month every 33 months.

Months familiar to us are as per Gregorian Calendar which is based on Solar Cycle. 

Earth takes 365 days to complete one revolution around the Sun.

These are divided into 12 parts and each part is called Month. 

Some months have 31 days while some have 30 except February which has 28 or 29 days.

Position of Earth along the orbit is also decided like 21st March, 22nd June, 22nd September and 22 December.

Months in Hindu calendar are based on the cycles of the Moon.  

Time taken by the Moon to complete one revolution from New Moon phase to next New Moon is considered as one month in Hindu Calendar. Also known as ChandraMaas .

On this dial, Zodiac signs as per the Hindu Calendar are named like this.  Mesh, Rishabh, Mithun, Karka,... popularly known as Rashi as well. 

Just like Gregorian Calendar, there are 12 months, Chaitra, Vaishakh, Jeshtya, Aashadh.......

While months are named as Chaitra, Vaishakh, Jeshtya, Aaashadh, Shravan ....

Let us start with Gudhipadva - Festival which marks start of New Year.

Let us take help of the calendar to learn about the same. 

Month is April and Year 2021.

There is New Moon or Amavasya on 12th April. Let us position the moon accordingly.

When Sun is in MEEN Rashi , First Month Chaitra starts from the new Moon phase that is amavasya.

13th April is the first day of Chaitra also known as Chaitra Pratipada.

There is a full moon or Purnima on 27th April and Amavasya or New Moon on 11th May, marking the end of first month Chaitra. 

Each Month of the hindu calendar has 30 days. Each day is also called as Tithi.

But how duration of a day is decided ? 

Moon orbits at a greater speed around Earth. Angle between Sun and Moon continues to increase from 0 degree to 360 degrees from new moon to next new moon. If we divide 360 degrees in 30 equal parts, each part will be of 12 degrees. 

Time moon takes to cover these 12 degrees is considered as one day or Tithi.

Like if it travels 12 degress, Pratipada - First day , after 24 degrees, Dwitiya - second day and so on ...

Due to elliptical orbits of moon as well as earth, speed is different at different locations. Sometimes it takes more time to cover 12 degrees while at other times it takes less time. That is the reason duration of a single day or tithi varies in Hindu Calendar . It fluctuates between 20 to 27 hours. In gregorian calendar each day is fixed as 24 hours. 

From New moon phase, 180 degree travel marks Full Moon and 360 degrees marks the next new moon phase.

This part is also the waxing phase of the moon and is known as shukla paksha. 

This part is also waning phase of the moon also known as Krishna paksh. 

Tithi in Shukla Paksha is prefixed with shuddha while Tithi in Krishna paksh is prefixed with Vadya.

Shudh Pratipada

Shudha Dwitiya

Shudha Ashtami and so on

Vadya Pratipada

Vadya Dwitiya

Vadya Ashtami and so on

Lets move ahead

Next month Vaishakh starts from 12th May 

26th May Purnima

10th June is new moon day , Amavasyya

Start of another month, Jeshtha

In every month, Sun transits from one raashi to another . 

Like in the month of Chaitra, from Meen rashi to Mesh, In Vaishakh , to Vrishabh rashi and in Jeshtha Mithun Rashi.

If this transition does not take place in a particular month, that month is considered as extra month or adhik maas for that year.

12 revolutions of moon mark the completion of 1 year in Hindu Calendar

First month of next year, Chaitra starts from this position again.

In year 2022, Chaitra starts on 2nd April, almost 11 days in advance than the previous year. This is because each month is only 29.5 days approximately.

Moving on, in the year 2023, Chaitra month starts on 22nd March, 22 days earlier than 2021. 

If same sequence is followed, we may have to celebrate hole in monsoon or Diwali in Summer.

This is where extra month or adhik maas comes handy.

Lets us move on.

Vaishakh, jeshtha, aashadh

17th July is amavasya or new moon day and Sun is in Kark Rashi. 

Moon completes one cycle on 17th August but Sun is still in Kark Rashi.

There is no transition of Sun to another Rashi during this period. This month is considered as Extra Month or Adhik Maas.

Adhik Shravan

Month after is considered as regular Shravan as per earlier sequence.

Now sun has transitioned to Sinha rashi from Kark Rashi

Other months follow the sequence as usual.

In 2024, gudhipadva will be on 9th April , somewhat closer to 2nd April in 2021.

Introduction of extra-month or Adhik Maas enables synchronization of Solar and Lunar cycles in Hindu Calendar.

If one considers the start of Chaitra Month from 2000 to 2010, Sun is always in Meen rashi. 

Just like transition of sun through rashis, transition of Moon through Nakshatra is also worth exploring.

We will learn more about this in the next video.

Thank you.