There are different ways in which a day is reckoned as per the Hindu calendar when compared to the conventional system which is used for all practical purposes. As per normal wisdom it is generally perceived and believed that a day commences at the stroke of midnight right at the dot of 12 AM at any part of the world and runs up till the next day when 24 hours passes paving the way for the next day to begin. This is evident with new year celebrations being held right at the stroke of 12 AM and even while wishing people Birthdays, there is a notion to wish them right on the money when the clock hits 12 AM. Even India is said to have obtained Independence right at the stroke of midnight at the mark of 12 AM when the date moved to 15th August 1947.
Having said all this, the interesting thing to note is that based on Hinduism there is a sea of difference when it comes to how a day is to be reckoned. For a Hindu day, the guiding reference point happens to be the time of Sunrise and a day is said to commence from sunrise until the next day of sunrise when the next day is said to commence. Because the sunrise time holds fort, one would see different places recording different times of start and end when reckoning a day. Even coming to general logic, in many of the calendars one would see a start time of 6 AM igniting the start of the day as it happens to be the closest approximate ball park time when sunrise is said to occur across India and most other countries. However to be exact and when fixing the time for important events, only sunrise time needs to be taken and 6AM should be considered just for ease of use and as an approximate calculation. Thus, there is a clear head and shoulders difference of at least 6 hours when a day is reckoned as per practical norms (12 AM) and when considering the time for fixing and calculating auspicious time intervals (6AM) as per the Hindu system.
Before delving into the different time divisions as per the Hindu system, let us briefly look into the different time horizons popular in the western world. These are not exactly defined but generally tends to be followed. On a larger framework, a day tends to be divided into 3 parts viz Morning, Afternoon and Evening. Morning is said to run from Midnight (12AM) until Midday (12PM) followed by a 6 hour slot for Afternoon running from 12PM to 6PM and the remaining 6 hours of the day namely from 6PM to 12AM being the time of Evening. This can be extended into 7 zones with the ending period being given separate names with 12AM being classified as Midnight, 12PM called as Midday, 6AM or around sunrise termed as Dawn and around 6PM or sunset being classified as Dusk. This can again be classified into 14 parts with Afternoon comprising of Early Afternoon, Mid Afternoon and Late Afternoon, Evening consisting of Early Evening, Mid Evening, Late evening and entire Morning portion which runs from 12AM to 12PM being classified as Late Night, Early Morning, Mid Morning and Late Morning and on top of that we have the 4 markers of Midday, Midnight, Dawn and Dusk. Sometimes it is also believed that the split of the day which is divided into 3 viz Morning, Afternoon and Evening can actually be split as 4 with equal windows for Morning, Afternoon, Evening and also a Night portion included from 12AM to 6PM.
Let's now look at the various time divisions in a day which are prevalent in the Indian system
2 part time division: (1 in day and 1 in night)
As mentioned earlier, the constitution of a Hindu or Vedic day runs from the commencement of sunrise until the next sunrise. The entire day from Sunrise to next day Sunrise is divided into 2 portions viz the part from Sunrise to Sunset and from Sunset to next day Sunrise. The former is known as day time and the latter is known as night time. The time duration may not be equal for both but for an equal day and night portion in a day, it can be said to comprise of 12 hours each with sunrise portion running from 6AM to 6PM and Sunset portion from 6PM to 6AM of next day.
4 part time division: (2 in day and 2 in night)
As per Tamil timekeeping, dividing the day into 4 portions is called as 'Naal Naanku Kaalam' translating to four periods of the day. They are classified as under:
1) Kaalaiyil (Morning): 6 AM to 12 PM
2) Mathiyil (Afternoon): 12 PM to 6 AM
3) Maalai (Evening): 6 PM to 12 AM
4) Iravu (Night): 12 PM to 6 AM
6 part time division: (3 in day and 3 in night)
As per Tamil tradition, an entire day happens to be divided into 6 periods ('Pozhudhugal') with 3 of the periods being during day time and 3 of the periods occurring during night time. The classification is as given below:
1) Kaalai (Morning): 6 AM to 10 AM
2) Nanpagazh (Noon): 10 AM to 2 PM
3) Yerpaadu (Afternoon): 2 PM to 6 PM
4) Maalai (Evening): 6 PM to 10 PM
5) Yamam (Night): 10 PM to 2 AM
6) Vaigarai (Dawn): 2 AM to 6 AM
Coming to Astrology treatise, as per the age old classic "Brihat Parashara Hora Shastra", one of the features in ascertaining the six fold strength of planets is through the rule of Tribhagha Bala where day and night is said to be divided into 3 equal parts with specific planets gaining strength accordingly based on the time of birth. The information of the same is shared below:
Day Time First Part: 6 AM to 10 AM - Mercury becomes strong
Day Time Second Part: 10 AM to 2 PM - Sun becomes strong
Day Time Third Part: 2 PM to 6 PM - Saturn becomes strong
Night Time First Part: 6 PM to 10 PM - Moon becomes strong
Night Time Second Part: 10 PM to 2 AM - Venus becomes strong
Night Time Third Part: 2 AM to 6 AM - Mars becomes strong
Jupiter is always said to be strong at any point of the day or night. Also as per one tradition, it is said that Jupiter is the torchbearer of the Panchang element of 'Vara' which makes perfect sense based on its assertion that it's always strong irrespective of whether birth takes place during day time or night time.
8 part time division: (4 in day and 4 in night)
There is another time division which divides an entire day into 8 parts allotting 4 parts to the day and 4 parts to the night. This is called 'Prahara' which is a Sanskrit term for unit of time. The first Prahara is said to begin at Sunrise and the 4th Prahara is said to end when Sunset begins. Likewise the 5th Prahara starts when Sunset begins and the last Prahara ends with the completion of Sunset leading to Sunrise of the next day. The names of the Praharas and the time slot of approximately 3 hours each is listed below
1) Purvaanha (Day): 6 AM to 9 AM
2) Madhyaanha (Day): 9 AM to 12 PM
3) Aparaanha (Day): 12 PM to 3 PM
4) Saayankaala (Day): 3 PM to 6 PM
5) Pradosha (Night): 6 PM to 9 PM
6) Nishitha (Night): 9 PM to 12 AM
7) Triyaama (Night): 12 AM to 3 AM
8) Usha (Night): 3 AM to 6 AM
10 part time division: (5 in day and 5 in night)
Somewhat similar to Prahara, there is another sub division as per the Hindu calendar which divides both the day time hours and night time hours into 5 equal parts. For an equal day and night, this would equate to 2 hours 24 minutes each. The names of it is given below
1) Prata (Day): 6 AM to 8:24 AM
2) Sangava (Day): 8:24 AM to 10:48 AM
3) Madhyahna (Day): 10:48 AM to 1:12 PM
4) Aparaanha (Day): 1:12 PM to 3:36 PM
5) Sayana (Day): 3:36 PM to 6 PM
6) Pradosha (Night): 6 PM to 8:24 PM
7) Ratri (Night): 8:24 PM to 10:48 PM
8) Madhya Ratri (Night): 10:48 PM to 1:12 AM
9) Apa Ratri (Night): 1:12 AM to 3:36 AM
10) Prata Sandhya (Night): 3:36 AM to 6 AM
Also, as per ancient tamil literature, there is a system called as 'Pancha Pakshi' where Pancha means the number '5' and Pakshi means 'Bird'. It is believed that the 5 elements of Air, Fire, Water, Earth and Ether are represented by these birds and each of these birds Vulture, Owl, Crow, Cock and Peacock performs an activity for the 2 hours and 24 minutes allotted which includes Eating, Walking, Ruling, Sleeping and Dying. The method of splitting the day time and night time into 5 parts is termed as 'Yama'.
For more detailed discourse on Pancha Pakshi Shastra, one can refer to the below link:
https://tuningmymelody.blogspot.com/2019/04/time-technique-of-pancha-pakshi-shastra.html?m=0
16 part time division: (8 in day and 8 in night)
This classification of time is of prime importance as it's actually used for decoding auspicious and inauspicious time slots within a day. There are three different methodologies which is earmarked in the calculation of the definition of time.
Kala Vela: This is used to mark the designated time zones by each of the 7 planets viz Sun, Moon, Mars, Mercury, Jupiter, Venus and Saturn. There are 8 periods of about 1 hour and 30 minutes each within Sunrise and Sunset but only 7 planets to be assigned. Hence the extra portion is considered to be headless and a blank or Lordless portion is assigned to it. There is however a thought process given to mention it as Rahu but that portion is not necessarily the time period for 'Rahu Kalam' and hence should not be confused. The time period ruled by Jupiter and Saturn are said to be Yama Ghanta Kala and Gulika Kala respectively which is used in ascertaining time slots for activities.
Gowri Panchanga: This is used especially in Tamil Nadu especially to delineate important activities to be performed based on allotting the time slots into 8 each for sunrise and sunset. Here the 8 parts are assigned to the 7 planets Sun, Moon, Mars, Mercury, Jupiter, Venus and Saturn and the 8th portion is given specifically to Rahu and that forms the basis for Rahu Kalam which is used quite extensively as a period to avoid in the South especially while performing auspicious tasks.
Chogadiya: This is again kind of similar to Gowri Panchanga but sticks to only 7 planets excluding Rahu and there is also no blank portion as given by Kala Vela. This is used like a Muhurtha timing in the North of India and the 8th portion within Sunrise again happens to be the planet ruling the first portion and the sequence follows in similar vein across the whole day.
It should be noted that the calculation differs for all of Kala Vela, Gowri Panchanga and Chogadiya depending upon the weekday in operation. A detailed exposition listing out the uses and it's calculation has been laid out below in this link:
https://tuningmymelody.blogspot.com/2019/11/the-8-unit-division-of-time-cycle-kala.html?m=0
24 part time division: (24 in entire day from Sunrise to next day Sunrise)
This concept is called as 'Hora' which divides the entire day from Sunrise to next day Sunrise allotting one hour each for all 7 planets viz Sun, Moon, Mars, Mercury, Jupiter, Venus and Saturn. The day always starts with the Hora ruling the day viz Sun for Sunday, Moon for Monday, Mars for Tuesday, Mercury for Wednesday, Jupiter for Thursday, Venus for Friday and Saturn for Saturday. There is a debate however whether this needs to be split as 12 each for Sunrise and Sunset respectively but it does not really serve the element of 'Hora' which technically means Hour or 60 minutes. If Sunrise time happens to be let's say 13 hours and Sunset only 11 hours, then almost 65 minutes will be assigned for a planet during day time and only 55 minutes during night time. It defeats the very existence of the name 'Hora' and the time span between one sunrise to next sunrise is always on the ball park of 24 hours with just a minute or two adjusted here or there which makes one hour for a planet being assigned far more weight age. The Hora gets calculated in the order of the most slowest planet to the most fastest planet which goes in the form of Saturn -> Jupiter -> Mars -> Sun -> Venus -> Mercury -> Moon.
A more detailed explanation of the concept of Hora and how it's calculation is obtained is available on the below link:
https://tuningmymelody.blogspot.com/2019/04/timing-events-with-gowri-panchanga-and.html?m=0
30 part time division: (15 in day and 15 in night)
This is termed as 'Muhurta' and is of utmost importance when fixing time for various events. There are 30 Muhurta's in a day with 15 being part of day time and the remaining 15 considered during night time. 'Muhurta' is a Hindu unit of time and denotes a division of a period of 1/30th of a day which is roughly 48 minutes each. Each Muhurta is said to further break into smaller units of time such as 1 Muhurta of 48 minutes can be segregated into 30 Kalas (1 Kala = 1.6 Minutes or 96 seconds) and each Kala can be further bifurcated into 30 Kashtas (1 Kashta = 3.2 seconds). The list of all Muhurta's and their timing of operation for an equal day & night is listed below.
1) Rudra: 6.00 AM to 6:48 AM
2) Ahi: 6:48 AM to 7:36 AM
3) Mitra: 7:36 AM to 8:24 AM
4) Pitr: 8:24 AM to 9:12 AM
5) Vasu: 9:12 AM to 10:00 AM
6) Varaha: 10:00 AM to 10:48 AM
7) Viswadeva: 10:00 AM to 11:36 AM
8) Vidhi: 11:36 AM to 12:24 PM
9) Sutamukhi: 12:24 PM to 1:12 PM
10) Puruhuta: 1:12 PM to 2:00 PM
11) Vahini: 2:00 PM to 2:48 PM
12) Naktanakara: 2:48 PM to 3:36 PM
13) Varuna: 3:36 PM to 4:24 PM
14) Aryaman: 4:24 PM to 5:12 PM
15) Bhaga: 5:12 PM to 6:00 PM
16) Girisa: 6:00 PM to 6:48 PM
17) Ajapada: 6:48 PM to 7:36 PM
18) Ahir Budhanya: 7:36 PM to 8:24 PM
19) Pushya: 8:24 PM to 9:12 PM
20) Ashwini: 9:12 PM to 10:00 PM
21) Yama: 10:00 PM to 10:48 PM
22) Agni: 10:48 PM to 11:36 PM
23) Vidhatr: 11:36 PM to 12:24 AM
24) Kanda: 12:24 AM to 1:12 AM
25) Aditi: 1:12 AM to 2:00 AM
26) Jeeva: 2:00 AM to 2:48 AM
27) Vishnu: 2:48 AM to 3:36 AM
28) Dyumadgadyuti: 3:36 AM to 4:24 AM
29) Brahma: 4:24 AM to 5:12 AM
30) Samudra: 5:12 AM to 6:00 AM
60 part time division: (60 in entire day from Sunrise to next day Sunrise)
Like how 24 hours constitutes a day, as per Hindu division each of 24 minutes are termed as 'Ghati' running from Sunrise till the next day Sunrise. There is no separate name available for every Ghati or and it's usually a unit of time. If a day from sunrise to next day sunrise exceeds or falls mildly short of 24 hours, then the Ghati is adjusted accordingly but in general a Ghati is said to constitute 24 minutes. In the olden days, horoscopes were written to decode the time based on Ghati's and Vighati's (60 Vighati's is 1 Ghati) elapsed as compared to the procedure today when the exact time is mentioned. Like Hora which is said to be an hour of time running across Sunrise to next day Sunrise, similarly Ghati comprises of 60 components with a running time of 24 minutes each. However it should be noted that for the calculation of Mandi alone, Ghati needs to be divided as 30 each in the period of Sunrise and Sunset as the formula for computation is clearly elucidated in the astrological work 'Uttara Kalamrita' written by Sage Kalidas which mentions that Mandi is said to rise accordingly in a day based on the Ghati's elapsed during day time and night time. It is also to be noted that this will always fall somewhere in the middle of the portion assigned to Saturn in the Kala Vela calculation viz Gulika Kala.
Sunday - 26 Ghatikas after sun rise, 10 Ghatikas after sun set
Monday - 22 Ghatikas after sun rise, 6 Ghatikas after sun set
Tuesday - 18 Ghatikas after sun rise, 2 Ghatikas after sun set
Wednesday - 14 Ghatikas after sun rise, 26 Ghatikas after sun set
Thursday - 10 Ghatikas after sun rise, 22 Ghatikas after sun set
Friday - 6 Ghatikas after sun rise, 18 Ghatikas after sun set
Saturday - 2 Ghatikas after sun rise, 14 Ghatikas after sun set
There is even a consideration to divide a day into 32 parts each for day and night so as to blend well with it being a multiple of 8 as a 'Yamardha' is technically said to be an eighth part of a day. This would equate well with the division of Kala Vela which divides the day and night into 8 equal parts and the Mandi will fall exactly in the middle of the Saturn's portion assigned as Gulika Kala. However it doesn't make complete sense as a day is said to be comprising of 60 Ghatika's only and 64 (32 each for day and night) is used just for ease of use and get the exact middle point. Irrespective Mandi will always fall only in the period of Gulika in and around the middle portion. For more information regarding the calculation of Gulika and Mandi, the below link can be referred.
https://tuningmymelody.blogspot.com/2018/09/ascertaining-gulika-and-mandi-in.html
Note: It should be noted that 'Ghati' is also known alternatively as Ghatika, Nazhika, Pala etc and is known as a unit of time equal to one sixtieth of a day. Also all the times mentioned above is based on the fact that Sunrise begins at 6:00 AM and Sunset at 6:00 PM. The computation of different facets of time should be factored based upon the actual sunrise time and not standard 6:00 AM. It is not expected to remember all the different units of time however remembering some of the important time dimensions can be helpful such as decoding Yama Ghanta Kala and Gulika Kala which occurs based on 'Kala Vela' computation, Rahu Kalam which arises based upon 'Gowri Panchanga', knowing time of Hora and Muhurta in operation can also be helpful but however can always be checked from an Almanac. It would however be good to know the Sunrise and Sunset timings each day of the particular place one is residing as that forms the crux for majority of the time divisions.
