Reading the Hindu Calendar

A reader who looks up the date of Diwali for two consecutive years notices something strange. One year it falls in late October. The next, in mid-November. Holi slides around March. The night of Shiva moves through late February and early March. By the rules of the Western calendar, the festivals seem to wander.

They do not wander. They are some of the most precisely fixed dates on earth.

What moves is the Gregorian calendar, which counts only the sun and ignores the moon entirely. The Hindu calendar counts both, and the festivals are pinned to the moon. To see that they are fixed, you have to learn to read the sky the way the almanac reads it. This chapter opens the machine.

Two clocks, one calendar

There are two great clocks in the sky. The sun gives the year, the cycle of the seasons, the slow swing of the days from long to short and back. The moon gives the month, the quick cycle from dark to full to dark again, twelve and a bit times in every solar year.

A calendar can follow one or the other. The Western calendar follows the sun and lets the months drift free of the moon, so a Gregorian month has nothing to do with a lunar phase. The Islamic calendar follows the moon alone and lets its year drift free of the sun, so its festivals move backward through the seasons over the decades. The Hindu calendar refuses to give up either. It is luni-solar. It counts its months by the moon and corrects its year to the sun, and almost the entire ingenuity of the system is spent on keeping these two clocks married.

That marriage is the source of the apparent wandering. A lunar year of twelve moons runs about 354 days. A solar year runs about 365. The eleven-day gap is the price of following the moon, and the festivals, locked to the moon, slide against the Gregorian calendar by roughly that much each year until a correction is made. The correction is the subject of the next chapter. The point here is simpler: the dates are fixed to the moon, and the moon is what you must learn to read.

The lunar day

Begin with the smallest unit, and the one most foreign to the Western mind. The Hindu day of the calendar is not the span from one midnight to the next. It is the tithi, the lunar day.

A tithi is defined by the relationship between the moon and the sun. As the moon races ahead of the sun across the sky, each time it gains twelve degrees of distance, one tithi has passed. Thirty of these twelve-degree gains carry the moon a full circle ahead, from one new moon to the next, and thirty tithis therefore make one lunar month.

Here is the consequence that trips up every newcomer. Because the moon does not travel at an even speed, speeding up and slowing down on its slightly oval path, a tithi is not a fixed length. It averages about twenty-three and a half hours, close to a solar day but never identical to it, and it ranges from roughly twenty hours to nearly twenty-seven. A tithi drifts against the sunrise.

And so two odd things can happen. Sometimes a tithi is long enough to span two sunrises, and that lunar day is counted twice, an adhika or repeated tithi. Sometimes a tithi is short enough to begin and end between two sunrises, touching neither, and that lunar day is dropped from the count entirely, a kshaya or lost tithi. The calendar has days that come twice and days that never come. This is not an error. It is what happens when you measure a day by the moon instead of the clock.

When a festival is fixed to a tithi, the almanac has to decide which solar day carries it, usually the day on which that tithi is current at sunrise, or at the specific hour the rite requires. Different regional almanacs, computing from different cities and different methods, sometimes land on different days. A festival falling on two dates in two states is not a contradiction. It is two careful readings of the same moon.

Fortnights and months

Fifteen tithis make a paksha, a fortnight, and here the calendar takes on a quality the solar calendar lacks entirely: it tracks the direction of the moon’s light as well as the count of days.

The bright fortnight, when the moon waxes from new to full, is the shukla paksha. The dark fortnight, when it wanes from full back to new, is the krishna paksha. Every tithi belongs to one or the other, and many festivals are named by both. Maha Shivaratri is the fourteenth tithi of the dark fortnight. Rama Navami is the ninth tithi of the bright. The light of the moon is written into the date.

Two pakshas, one bright and one dark, make a lunar month, a masa. There are twelve: Chaitra, Vaishakha, Jyeshtha, Ashadha, Shravana, Bhadrapada, Ashvina, Kartika, Margashirsha, Pausha, Magha, and Phalguna. Each takes its name from the nakshatra, the lunar mansion, near which the full moon of that month falls. The month of Chaitra is the month whose full moon sits near the star-group Chitra. The names are a record of where the full moon stands against the stars.

There is one more wrinkle the reader will meet throughout this treatise, and it is worth naming now so it never confuses. Two regions divide the month at two different points. In the north, the month ends at the full moon, the purnimanta reckoning. In the south and west, it ends at the new moon, the amanta reckoning. The tithi of a festival is the same in both. Only the name of the month can shift. This is why Maha Shivaratri is called a festival of Magha in the south and of Phalguna in the north. It is one night. The two systems simply label the surrounding month differently.

The stars and the five limbs

Behind the moon’s phases lies a second lunar cycle, against the stars rather than the sun. As the moon circles the sky it passes through twenty-seven nakshatras, the lunar mansions, each a segment of the heavens a little over thirteen degrees wide, beginning with Ashvini. The moon moves through roughly one nakshatra a day. The nakshatra a person is born under, the nakshatra the moon stands in on a festival night, these carry weight in the tradition. Rama is born, the Ramayana says, under the nakshatra the goddess Aditi looks kindly on. The star is part of the sacred coordinate.

Put all of this together and you have the panchanga, the almanac whose name means “five limbs.” The five are the tithi, the lunar day; the vara, the weekday; the nakshatra, the lunar mansion the moon occupies; the yoga, a value got by adding the longitudes of sun and moon and dividing the sky into twenty-seven parts; and the karana, a half-tithi. These five together fix the character of the day as well as its date, its fitness for a wedding, a journey, a vow, a festival.

A festival date, then, is not a square on a grid. It is an intersection in the sky. Diwali is the new moon, the amavasya, of the month of Kartika. Guru Purnima is the full moon of Ashadha. Janmashtami is the eighth tithi of the dark fortnight of Bhadrapada, and the strongest reckonings also want the moon in the nakshatra Rohini, the star under which Krishna was born. The almanac reads the heavens and announces where, in the turning of the moon and the wheel of the stars, the sacred moment has come round.

What the machine is for

It would be easy to mistake all this for mere computation, the dry arithmetic of an old astronomy. It is arithmetic, and the Indian astronomers who refined it, the tradition running from the Vedanga Jyotisha of Lagadha through the Surya Siddhanta, were among the finest the ancient world produced. But the arithmetic serves something the previous chapter named.

The calendar is the instrument that keeps a human life in time with ritam, the cosmic order. The tithi is not a number. It is the exact relationship of the moon to the sun at a sacred moment. The almanac does not invent the festival’s date. It finds it, the way an astronomer finds a returning comet, by reading where the lights stand.

So when the dates seem to wander, the reader now knows the truth. They are holding still against the only calendar that matters to them, the sky. It is the modern wall calendar that drifts.

The next chapter turns from the moon to the sun, and to the one problem this whole system has been quietly carrying: how to keep a year of moons in step with a year of seasons, when the two will never come out even.