Notes on the Horary Periods Calculator
Sunrise and Sunset calculations
The Sunrise and Sunset calculator works using a PHP implementation of an algorithm published in the Almanac for Computers, 1990, published by Nautical Almanac Office, United States Naval Observatory, Washington, DC 20392. I have experimented with the results and have found that they are consistently correct to within a minute of Meteorogical Office data. But if it's important to you, please double check.
Moon Phase calculations
The moon phase algorithm (used for Tithi) is my own PHP implementation of that used by John Walker in his MoonTool for Windows. The algorithm is from Meeus, Jean. Astronomical Algorithms. Richmond: Willmann-Bell, 1991. ISBN 0-943396-35-2. I have found it to be accurate to within a few seconds. Phase images are courtesy of NASA.
Period definitions
The definitions used to calculate the Horary periods are described below. I do not claim that these are the correct and only way of doing these calculations, as different opinions exist in the community. If you would like to see an alternative definition, please let me know.
In accordance with the Vedic day starting at Sunrise, if a time is entered that is before Sunrise on the calendar day, then the previous day's Sunrise/Sunset data will be used for calculations.
The Map will allow you to determine the coordinates of your location with great accuracy (rounded to the nearest minute of arc). I prefer this data to the general coordinates published for many of the larger cities.
Hora
There are several Hora calculations supplied, but all have the same basis. The day is divided into 24 equal Horas (i.e., of one hour each). The type of Hora defines the time at which the cycle begins:
- For Satya ("true") Hora, this is Sunrise.
- For Kaala Hora, this is 6:00 am Local Mean Time.
- For Mahakaala Hora, this is 6:00 am Local Standard Time.
The first Hora of the day is lorded by the planet that lords the day itself:
| Day | First Hora Lord |
|---|---|
| Sunday | Sun |
| Monday | Moon |
| Tuesday | Mars |
| Wednesday | Mercury |
| Thursday | Jupiter |
| Friday | Venus |
| Saturday | Saturn |
Subsequent Horas then follow cyclically the following order, for the remaining 23 Horas in the day:
Sun » Venus » Mercury » Moon » Saturn » Jupiter » Mars
Tattva
There are five Tattvas (elements): Prithvi (Earth), Jala (Water), Agni (Fire), Vayu (Air), Akasha (Space). The day is divided into two parts, daytime and night-time, demarcated by Sunrise and Sunset. Each part is further divided into 120 equal portions. These portions repeat themselves in groups of 30. The Tattvas are allocated unequally in each group of 30 in the following order:
| Tattva | Portions (1/120th of day or night) |
|---|---|
| Prithvi | 1 |
| Jala | 2 |
| Agni | 3 |
| Vayu | 4 |
| Akasha | 5 |
| Akasha | 5 |
| Vayu | 4 |
| Agni | 3 |
| Jala | 2 |
| Prithvi | 1 |
It should be noted that the length of one portion can be quite small (a few minutes), and therefore this calculation is particularly sensitive to Sunrise and Sunset times.
Yama
The day is divided into two parts, daytime and night-time, demarcated by Sunrise and Sunset. Each part is further divided into eight equal portions. The lord of the first portion (of either daytime or night-time) is the lord of the day itself. Subsequent Yamas then follow the following order:
Sun » Mars » Jupiter » Mercury » Venus » Saturn » Moon » Rahu
Kaala
The day is divided into two parts, daytime and night-time, demarcated by Sunrise and Sunset. Each part is further divided into eight equal portions. The lord of the first portionis determined as follows.
| Day | First Kaala Lord (daytime) | First Kaala Lord (night-time) |
|---|---|---|
| Sunday | Sun | Venus |
| Monday | Moon | Jupiter |
| Tuesday | Mars | Saturn |
| Wednesday | Mercury | Rahu |
| Thursday | Jupiter | Moon |
| Friday | Venus | Sun |
| Saturday | Saturn | Mars |
Subsequent Kaalas then follow the following order:
Sun » Mars » Jupiter » Mercury » Venus » Saturn » Moon » Rahu
Thus Kaala and Yama are identical during the daytime half of the day.
Bugs? Feature requests? Let me know!.