Tithi is the date as per the lunar calendar adopted in Vedic Astrology. Ancient India used this calendar very widely. A large number of India’s religious and social festivals are celebrated based on Tithi.
People of India follow their customs based according to the rules of the Tithi. The basis of Tithi is the path of the Moon, and not that of the Sun, that is there is a difference between the progress of the Lunar calendar and the solar calendar, in fact sometimes there are two Tithis in one day.
Calendar “date” which we all use in our daily life is in fact based on English solar calendar. Here the main basis of the solar calendar is the very rotation of the Earth around the Sun. It takes approximately 365 ¼ days for the earth to complete one rotation around the Sun. Thus, the present day of calendar of the English is divided into 365 days, divided into twelve months. After every four years one day is added to this calendar to make up for the difference of the 1/4 th part of the day that is lost each year.
Just like solar calendar, lunar calendar is very much used in a large number of Asian countries such as India, the Middle East, China, Pacific-rim countries. In fact, lunar calendar is believed to have its roots in India. Not only that, it is assumed that it was used even before the use of solar calendar as a part of Tithi.
The basis of lunar calendar is on moon’s rotation around the earth. The lunar month remains in touch with the rotation on moon around the Earth. As the duration of the rotation of the moon around the earth varies, the duration of the lunar month also varies. On a general basis, the lunar of month has near about 29 ½ days.
Usually, the lunar year has 12 lunar months of nearly 354 days, hence making it shorter by around 11 days with respect to the solar year. Yet, the calendar accounts for this difference by adding an extra lunar month about once in every two and half years. The additional lunar month is usually termed as “Adhik Mas” in India. Going by the Indian lunar, it starts on the new moon day that takes place just at the beginning of the Spring. The twelve lunar months are as follows:
As described earlier, to account for the difference between the lunar and solar year, an additional lunar month happens near every two and half years as “Adhik Mas” (Extra month).
Following the Muslim calendar, in most Muslim countries, the lunar year is strictly followed on the basis of twelve lunar months of 354 days every year. Because of that, their holy month of Ramadan falls nearly 11 to 12 days in advance than the previous year related to Tithi.
The English solar day maintains a fixed length of 24 hours. The shift in date occurs mainly at midnight according to the local time or standard time of a given local time zone. So, the date changes from m midnight to midnight . To put it simply, in the English calendar, the date and the length of the day is accurately 24 hours.
The starting of the lunar day is at sunrise. The length of a lunar day is controlled by the time passed between sunrises. According to the Jewish calendar, their lunar day starts at the time of the sunset and continues through to the next sunset. So, a lunar day is understandably similar to a weekday. In India, the lunar day is normally termed as “Vaar”.
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The lunar date varies roughly between 22 to 26 hours based on the angular rotation of moon around the earth in its elliptical track. In the Indian calendar, the lunar date is termed as “Tithi”. It is calculated after taking the distance between the moon and the sun as viewed from the earth. Also, it at least takes one lunar month or roughly 29 ½ days for the distance between the sun and the moon to shift from 0 to 360 degrees.
When the distance between the sun and the moon becomes zero, a new lunar months starts. That means that a lunar month begins in new moon. Apart from this, the angular distance between the sun and the moon as viewed from the earth turns 180 degrees related to Tithi.
The lunar cycle starts with the moon in a crescent shape. The crescent phase ends when the moon turns into an orb or a full moon. It usually stays in this phase for nearly 15 days. After that it again starts decreasing in size. Later the moon disappears from the sky and lines up with the sun. The decline phase is only for a short duration As per the Indian lunar month, the fornight of the crescent lunar phase is termed as “Shukla Paksh” while the fortnight of the declining phase of the lunar cycle is termed as “Krishna Paksha”. So, at the time of Shukla Paksha, the distance between the sun and the moon increases from 0 degrees to 180 and at the time of the “Krishna Paksha”, it decreases from 180 to 0 degrees. In case, one divides 180 degrees into 15 equal parts, then each part turns out to be of 12 degrees.
That way each part divided into 12-degree is the lunar Tithi or date. Lunar dates or Tithis in Shukla Paksh start with ‘Prathama’ (first), ‘Dwitiya’ (second) etc., till Poornima (Full Moon). Likewise, for the declining fortnight lunar cycle, Tithis start again with ‘Prathama, Dwitya etc., till the moon reaches the new moon phase or ‘Amavasya.’
The pointed velocity of the moon in its oval (egg-shaped) track varies as it gets affected by the comparative distance between the moon and the earth and also by the earth‘s comparative distance from the sun. As a result, the regular angular speed (the speed of the angle between the sun and the moon as viewed from the earth) fluctuates somewhere between 10 to 14 degrees. Given that, the length of a Tithi corresponds to 12 such degrees. The duration of a Tithi varies accordingly. Hence, a Tithi can be for over one day or for that matter, it can skip if 2 Tithis take place in a day.
As the angular covered distance between the sun and the moon is always comparative to the whole earth, Tithi or a lunar day begins at the same time all over the world. However, it may not be on the same day. So, if a particular Tithi begins at 10:30 pm in India, it will also start at that time in New York simultaneously, which is 12 pm (EST) on the similar day. Also, as the length of a Tithi can fluctuate between 20 to 28 hours, its conversion to a Vaar turns a bit puzzling.
According to the Indian calendar, the Tithi for a particular location relies on the angular distance between the moon and the sun in reference to sunrise. For example, if a sunrise on a Monday in the month of November in New York takes place at 8:30 am and at 9 am on the same day the angular distance between the moon and the sun is 12 degrees because of the new moon of the Indian lunar month, Kartik. As the time-span of a Tithi is twelve degrees; the Tithi, Kartik Shudha Dwitya will start exactly at 9 am on Monday Hence, the Tithi for that day in New York will be Kartik Shudha Prathma (first day).
Similarly, on that Monday morning the sunrise in Los Angles will take place after 9 am (EAST). Also, as the Dwitiya happens all over the world at the same time, hence, for Los Angeles, the Tithi for that particular Monday will turn to be Kartik Shudha Dwitiya.
Apart from this, on that very Monday, at 9 AM (EST), it would be 7:30 pm in New Delhi and Mumbai. Accordingly, Tithi for that Monday for New York, New Delhi and Mumbai will be Kartik Shudha Prathama (the initial day of Indian lunar month, Kartik). For the majority of locations in the West of St.Louis and Chicago, the Tithi for that Monday will be Dwitiya. The Tithi, Kartik Shudha Prathama, for West St.Louis and Chicago will take place on the previous day, that is Sunday.
The first day of the Indian lunar month Kartik (Kartik Shudha Prathma) also turns out to be the day after Diwali. A large segment of the Indian population celebrates this day as their New Year. Indians living in Europe, USA or India should celebrate their New Year on that particular Monday while people living in regions West of Chicago should celebrate it on the previous day, i.e. Sunday