The five parts of an almanac are:thithhi, vaaram, nakshathram, lagnam and yogam or karaNam.
The 12 raaSis are distributed among the 360 degrees of a spherical earth into 12 equal parts of 30 degrees each.The first raaSi of the first day in a month is the one in which the rays of the sun fall at daybreak.For example on the first day of chaithra month it is mesha raaSi.
Since there are 365 days in the year and 24 hours in a day each raaSi has 2 hours duration.The raaSi changes for every 2 hours as the day advances.There will be a reduction of 4 minutes per day in the raaSi as the month proceeds.This is how the month is generated.In one month 120 minutes or 2 hours of a raaSi are over.in a month.Another example:
In the month of AaDi on the 10th day of the month there will be only (120 minus 40)80 minutes in the kaTaka raaSi.This is reckoned from the moment of sunrise.
Lagnam is the raaSi which we select for performing a particular activity as auspicious.
Sthhaana Suddham is the situation in which the raaSi chosen as the lagna does not have any planet in it.
Next in the alkmanac the planetary shifts from one raaSi to another are also indicated. Raahu, kethu and Saturn are slow moving while Sukra, Budha and Guru move faster.The dates on which a planet changes from one raaSi to another are indicated in the almanac.But the movement of the moon is so fast that it is not indicated.
The position of the moon is known from the position of the 27 stars.ASwini, BharaNi and a quarter of Kaarththikai belong to MesharaaSi.The star of a given day is given in almanac.From that we know the raaSi of the moon..
In a week wednesday, thursday and Friday are good days.
In a fortnight prathhamai, ashTami, navami, chathurthhi, chathurdaSi, amaavaasyai and pournami should be avoided.
Among stars BharaNi, Kaarththikai,Pooram,Aayilyam,KeTTai,Moolam, PooraaDam,PooraTTaadi should be avoided.
The yogas are siddha, amRtha and maraNa yogas.There is a table in the almanac which gives the yoga corresponding to a given day and star.Siddha and amRtha are the ones to choose.
What is Panchakam?
To each thithhi we assign the number;similarly for the day of the week, star and lagnam.Add these four numbers and divide by 9.If the remainder is an odd number it is good panchakam.(Reason for this division is complicated and so not discussed).
We should not predetermine a day and find the lagnam.Every thing should be determined together.
Dinam match should be done for the woman's star for functions like marriage, gRhapraveSam, Seemantham etc.For ShashTiabdapoorththi it is the man's star.Starting from it count until the star of the scheduled day abd divide by 9.The remainder in this case should be an even number or nine.
Raahukaalam should be reckoned from sunrise and not blindly as seven thirty to nine etc.Of the one and a half hour only three minutes are crucial but cannot be pinpointed.This is the reason why some persons claim they did some thing in Raahu kaalam and nothing bad happened.It only means that those three minutes had been avoided by him without himself knowing it.