

Maas in Panchaang
Maas or Month, a Lunar
month, is also a part of Panchaang. These are also 12 in number, like
Gregorian or solar calendar and come in a specific sequence. Their names are 
(1) Chait, or Chaitra, (2)
Baisaakh, or Vaishaakh, (3)
Jeth, Jyeshth, (4) Asaadh, or Aashaadh, (5) Saavan, or Shraavan, (6)
Bhaadon, or Bhaadrapad, (7) Kuaar, or Aashwin, or Asauj, (8)
Kaatik, or Kaarttik, (9) Agahan, or Agrahan or Maargsheersh, (10) Poos, or
Paush, (11) Mahaa, or Maagh, (12) Phaagun, or Phaalgun.
Otherwise there are several
types of lunar month, but usually the term lunar month refers to the
Synodic month, because it is the average time between Moon phases.
Synodic Month
A Synodic month is defined as the average time between the two New Moons
and is observed 29.53059 days (29 days, 12 hours, 44 minutes, 2.8
seconds) long. A New Moon or a Full Moon happens when the Moon crosses the
plane that is perpendicular to Earth's orbital plane and passes through
the centers of the Earth and the Sun.
Draconic Month
The Draconic month or nodal month is the period in which the Moon returns
to the same node of its orbit; the nodes are the two points where the
Moon's orbit crosses the plane of the Earth's orbit. Its duration is about
27.21222 days on average.
The tropical month is the average time for the Moon to pass twice throught
the same equinox point of the sky. It is 27.32158 days, slightly shorter
than the sidereal month of 27.32166 days, because of precession of the
equinoxes. Unlike the sidereal month, it can be measured precisely.
The sidereal month is defined as the Moon's orbital period in a
nonrotating frame of reference (which on average is equal to its rotation
period in the same frame). It is about 27.32166 days (27 days, 7 hours, 43
minutes, 11.6 seconds). The exact duration of the orbital period cannot be
easily determined, because the 'nonrotating frame of reference' cannot be
observed directly. However, it is approximately equal to the time it takes
the Moon to pass twice a fixed star (different stars give different
results because all have proper motions).
An anomalistic month is the average time the Moon takes to go from perigee
to perigee  the point in the Moon's orbit when it is closest to Earth. An
anomalistic month is about 27.55455 days on average.
A Synodic month is longer than a sidereal month because the EarthMoon
system is orbiting the Sun in the same direction as the Moon is orbiting
the Earth. Therefore, the Sun appears to move with respect to the stars,
and it takes about 2.2 days longer for the Moon to return to the apparent
position of the Sun.
A Draconitic month is shorter than a Sidereal month because the nodes move
in the opposite direction as the Moon is orbiting the Earth, one
revolution in 18 years. Therefore, the Moon returns to the same node
slightly earlier than it returns to the same star.
An anomalistic is longer than a sidereal month because the perigee moves
in the same direction as the Moon is orbiting the Earth, one revolution in
nine years. Therefore, the Moon takes a little longer to return to perigee
than to return to the same star.
Thus one Yog stays for just a little over a day.
