Masa (Lunar Month)

What is a masa?

A masa is a lunar month — the frame one rung above the tithi, and the one that carries the festival calendar. Twelve of them, Chaitra through Phalguna, structure the Hindu year; each runs a little over 29.5 days (thirty tithis) and is named for the sidereal sign the Sun enters while that lunar month is in progress.

That solar naming is the crux of everything below: the tithis inside a masa are lunar, but the masa’s name is pinned to the Sun. When those two rhythms fall out of step — and over a year they must — the calendar needs the corrections that give us the amanta/purnimanta split and the Adhika month.

The twelve masas and their seasons

The twelve masas pair two-by-two into the six ritus (seasons):

Each masa splits into two fortnights — the bright Shukla Paksha and the dark Krishna Paksha — exactly as described under tithi. Which fortnight closes the month is the whole question behind the next section.

Amanta and purnimanta — two ways to end a month

Two conventions divide the same moon into months, differing only in where they cut:

• Amanta (“ending at the new moon”) — common in the south and west. A month runs from one Amavasya to the next.
• Purnimanta (“ending at the full moon”) — common in the north. A month runs from one Purnima to the next.

They agree perfectly through the bright fortnight. The difference shows only in the dark fortnight, where the purnimanta name runs one month ahead of the amanta name — because purnimanta has already started its next month at the full moon, while amanta has not. So the same dark-fortnight day that amanta calls Chaitra Krishna purnimanta calls Vaishakha Krishna. This is why the month attached to festivals like Holi or Krishna Janmashtami reads differently between regions, though the day itself is the same. AstroShruti computes both names for every date, so you can read whichever your tradition uses.

Adhika Masa — the extra month

Twelve lunar months add up to about 354 days — roughly eleven short of the solar year. Left alone, the masas would slide backwards through the seasons. The fix is a leap month:

• Whenever a lunar month (Amavasya to Amavasya) contains no solar sankranti — the Sun does not change sign inside it — that month is an Adhika Masa (“extra month”), also called Mala or Purushottama Masa.
• It takes the name of the month that follows, with the prefix Adhika, so the year briefly has two Chaitras (an Adhika Chaitra then a Nija/regular Chaitra).
• It falls roughly every 32–33 months — about every three years — and realigns the lunar and solar years.

AstroShruti detects an Adhika month by exactly this rule (no sankranti between the bounding new moons) and labels it automatically. Its far rarer mirror image, a Kshaya Masa — a month dropped when two sankrantis fall inside one lunar month, possible only near perihelion and only once in many years — is a recognised phenomenon but not one AstroShruti flags today.

Masa, ritu and samvat

The masa is also the hinge of the era-counts. For the Vikram and Shaka samvats the year turns with Chaitra Shukla Pratipada — Gudi Padwa in Maharashtra, Ugadi in the Deccan. As a rough guide the Vikram samvat runs about 57 years ahead of the Gregorian year and the Shaka about 78 years behind, so a masa also tells you which samvat year you are in and which of the six ritus colours the season.

Reading a masa in AstroShruti

Open the Panchang for any date and location and the masa sits among the calendar fields, shown in both reckonings and flagged if it is Adhika. An illustrative reading looks like this:

Masa: Shravana (amanta) · Bhadrapada (purnimanta) — Krishna Paksha · ritu Varsha

Read plainly: it is a dark-fortnight day; the amanta system calls the month Shravana and the purnimanta system — one ahead in the dark half — calls it Bhadrapada; the season is Varsha, the monsoon. On an Adhika month the same line would read Adhika Shravana. The result is specific to the date and location you chose, because which lunar month a civil date falls in turns on the local sunrise relative to the new moon.

Open the Panchang for any date and location to see the masa in both reckonings, the ritu, the samvat years, and the tithis that fill the month.

Common mistakes

• Assuming one universal month-name. Amanta and purnimanta disagree through the whole dark fortnight; always note which system a source uses.
• Expecting the masa to track the Gregorian month. It is lunar and Sun-sign-named; it drifts, and the Adhika month is the correction, not an error.
• Reading Adhika Masa as inauspicious “throughout.” Traditions differ — it is Purushottama Masa, dear to Vishnu, in much of the north — so treat the label as a calendar fact, not a blanket verdict.
• Confusing the lunar masa with the solar month. Solar calendars (Tamil, Bengali) count months by the Sun’s ingress, not by the moon; the names overlap but the boundaries do not.

What AstroShruti computes — and what it doesn’t

AstroShruti computes the astronomical masa: for any date and location it finds the bounding new moons, names the amanta month from the sankranti inside them, derives the purnimanta name, detects an Adhika month by the no-sankranti rule, and reports the ritu and the Vikram/Shaka samvat years — all from the same engine that drives the charts, and verified against a published almanac’s month-names.

What it does not do is settle usage or the rarest edge. Which reckoning your family follows, whether a festival is kept in the Adhika or the regular month, and the handling of a Kshaya month are tradition-level and regional judgments. We give you both month-names and the exact lunar boundaries so those judgments rest on solid ground.

Related concepts

• Tithi — the lunar day and the two pakshas the masa is built from.
• Nakshatra — the Moon’s mansion; several masas take their names from the nakshatra the full moon falls in (Chaitra from Chitra, and so on).
• Karana — the half-tithi; sixty of them fill one masa.
• Vara — the weekday, the first limb of the panchang.
• Yoga — the Sun–Moon combination that colours each day within the month.