Lunar month

A lunar month runs from one new moon to the next: from the moment the Moon catches up with the Sun until it catches up with it again, about 29½ days later. It holds the thirty tithis (lunar days), and its Sanskrit name is maasa. The chart page gives the lunar month of the birth in its panchaanga.

From new moon to new moon

A month starts at a conjunction of the Sun and the Moon: the moment the two stand at the same longitude in the nirayana (sidereal) zodiac, which is the new moon. The Moon then pulls ahead, is opposite the Sun at the full moon halfway through, and closes in again from behind until the next conjunction starts the next month. Since each month ends with Amavasya, the new-moon tithi, this way of counting months is called amanta, "ending at the new moon".

Named by the conjunction's rasi

A month is named after the rasi (sign) in which the conjunction that starts it falls: a conjunction in Pisces starts Chaitra, one in Aries starts Vaisaakha, and so on round the zodiac, as the table shows.

The names themselves are those of nakshatras (lunar mansions). About a fortnight after the conjunction the Moon is full and stands across the zodiac from the Sun, and in each month it then usually stands in the nakshatra the month is named after. Take Kaarteeka: it starts with the Sun and the Moon together somewhere in Libra, so by the full moon the Moon has reached the other side of the zodiac, around the end of Aries and the start of Taurus, which is Krittika. The conjunction can fall anywhere in its rasi, so this is only the likely nakshatra, and for three months the table gives two neighbouring ones.

The table

The table gives the same facts as the book's Table 4: the rasi of the conjunction that starts each month, the month's name, the nakshatra the full moon most likely falls in, and roughly when the month comes in the Gregorian calendar. The nakshatras are spelled as on the nakshatra page, so a few differ from Table 4's spellings.

Adhika and Nija months

The Sun takes a little over 30 days on average to cross a rasi, a day or so longer than a lunar month. Now and then a whole lunar month therefore passes with the Sun inside a single rasi. The conjunctions that start and end that month then fall in the same rasi, and two months in a row get the same name. Twelve lunar months come to about 354 days, some 11 days short of the Sun's trip round the zodiac; in a little under three years that shortfall adds up to a whole month, and the repeated name is how the lunar calendar catches up with the Sun.

Of two such months, hora calls the first, the one in which the Sun enters no new rasi, Adhika (extra), and the second Nija (real), and the chart page puts that word before the month's name. The book does not say which of the two is which; hora follows the common rule.

The solar month, year and day

The Sun gives a calendar of its own, which the book describes just before the tithis (§1.3.7). Its smallest unit, the solar day, is the time the Sun takes to move 1°. Thirty of them, the Sun's passage through one rasi, make a solar month, and 360, once round the zodiac, a solar year. As the Sun's speed changes over the year, a solar day is close to a day of clock time but not equal to it. Dasas (periods of life) and annual charts, later in the book, count time this way; the chart page does not show it.

Worked examples

On 1 January 2000 at 12:00 UT, at Greenwich, the panchaanga gives the lunar month as Maargasira (see the chart). The new moon that started that month came on 7 December 1999 at 22:32:22 UT, part way through that second. A chart for the second after it, 22:32:23, has the Sun and the Moon both at 21°31′26″ in Scorpio, the first tithi of the month, Sukla Pratipat (1), and the lunar month Maargasira: a conjunction in Scorpio starts Maargasira. The tithi on 1 January, Krishna Ekadasi (26), shows the month near its end, with four tithis to go.

2023 had two Sraavana months. The new moon of 17 July 2023, at 18:32:32 UT, fell early in Cancer: a chart for 18:32:33 has the Sun and the Moon both at 0°45′29″ in Cancer, and gives Adhika Sraavana. The next new moon, on 16 August 2023 at 09:38:54 UT, fell late in Cancer: a chart for 09:38:55 has the Sun at 29°06′30″ and the Moon at 29°06′31″ in Cancer, and gives Nija Sraavana. The Sun spent the whole month between them in Cancer, so both conjunctions started a Sraavana.

In the chart

The panchaanga on the chart page gives the lunar month of the birth on its last row, with Adhika or Nija in front when the birth falls in one of a pair; its value there links to this page.

Next comes the Sun-Moon yoga: a limb counted from the sum of the Sun's and the Moon's longitudes instead of their difference.

Book reference: P.V.R. Narasimha Rao, Vedic Astrology: An Integrated Approach, chapter 1, § 1.3.8.2. Where to get the book