This is the time taken by the Sun to make a circuit of the Tropical Zodiac. This is 365 days 5 hours 48 minutes and 45.2 seconds. This is 20 minutes and 24.6 seconds less. This is because the First Point of Aries moves 50.3 seconds per year.



Sidereal Period of the Moon

The time taken by Luna to make a circuit of the Sidereal Zodiac. This is 27 days 7 hours 43 minutes 11.5 seconds.

Synodic Period

SP is the the time between 2 successive conjunctions. For the Moon, it is the time taken from New Moon to New Moon.

Solar Month & the Laws of Planetary Motion

SM is the time taken by the Sun to traverse one Sign. The motion of the Sun is fastest at Perigee ( near the earth ) and slowest at Apogee ( away from the Earth). ( This is the Earth-in-reflex, as it is the earth which is moving and not the Sun ) . In other words, the motion of the earth is fastest at Perihelion and slowest at Aphelion. During the sidereal months of Sagittarius and Capricorn, the Sun is nearest to the earth. It takes only 29 days to traverse 30 degrees of a sign. During the months of Gemini and Cancer, the Sun is away from the earth and it takes 31.477 days for the Sun to traverse 30 degrees of a sign. The slowest motion of the Sun is 57 minutes and 11 seconds. The fastest motion of the Sun is 61 minutes 10 seconds. That is why some Sagittarius and Capricorn ( Vedic months ) have 29 days and Cancer and Gemini ( Vedic months ) have 32 days, as per the Vedic Calender.

The orbit of a planet is always elliptical, with the Sun as the focus of the ellipse. ( Suryaha Jagata Chakshu ).

The orbital period of a planet ( Bhagana Kala ) bears relationship to the Madhyama Manda Karna ( Semi-major axis ) of the planet. ( O P = MMK^1.5 ). ( These principles, discovered by Aryabhata, Bhaskara & Brahmagupta earlier were rediscovered in the West by Kepler as the Laws of Planetary Motion. )

Kali Era & Kali Day

The beginning of the Kali Era was 3102 BC, February 18 on a Friday. Then the First Tropical & Sidereal Points were in 0 degrees Beta Arieties ( Aswini ). All planets were in the same point at that time. If you add 3102 to the English era, you get the Kali Era. Ahargana is the elapsed Kali day number, the days elapsed from the start of the Kali Era. If you divide Ahargana by 7 and find the modulus, you can know the day of the week. If the remainder is one, it is Saturday, if it is two, it is Sunday and so on.

Day of the Week = Ahargana%7 ( % is the modulus operator in Foxpro ).

Njattu Vela

The constellation tenanted by the Sun is called Njattu Velu. In a day, the Sun traverses less than one degree ( less 59.13 seconds ). Sol takes 13,14 days to traverse 13 degrees 20 minutes and so the duration of a Njattu Vela is 13, 14 days.

Njattu Velas are important from the perspective of Agriculture. Karthika Njattu Vela is the time when the Sun transits the constellation of Karthika & Thiruvathira Njattu Vela is the time when the Sun transits the constellation of Aridra ( Thiruvathira ). Aridra, Karthika, Chothi and Chitra Njattuvelas give plenty of rains and farmers use this time productively.