Indian astrologers use Panchaang to see many things for days, and to predict future events for the year. A Panchaang is also used in determining auspicious and inauspicious time (Muhoort) as it indicates positions of planets and Nakshatra along with their influences on human lives. Panchaang is a compound word by joining two words - Panch and Ang. Panch means five, and Ang means parts. Since it tells about five parts about a day, it is called Panchaang. It is called "Patraa", or "Panjikaa" also. The five parts of a day it tells are as follows ---

(1) Tithi (1 to 14 + Amaavasyaa or Poornimaa); 

(2) Vaar (day-Sunday, Monday etc); 
see also     Vaar

There is a Shlok showing the Hindi names of the Vaar. It speaks about Kaal Horaa, but if somebody wants to know its origin, he should go through AVP and Yaagyavalkya Smriti before looking in Prashn Reeti ---
Ark Shukra Budhaschandra Mando Jeevo Dharaa Suta:
[Prashn Reeti written by Kokaniyal, and  Maadhaveeyam - not in Prashn Maarg written by Panakkattu Nambutiri - Kokaniyal was his student]

Even though there are 9 Graha, Raahu and Ketu are considered as Chhaayaa Graha (Chhaayaa means shadow so Chhaayaa Graha means Shadow Planets). Therefore, all the other 7 Graha which are visible are considered main, which makes a Week. As per Indian tradition the Week starts from Sunday and ends on Saturday. There is a significance in the sequence of Days arranged from Sunday to Saturday - that is the brightness of the planet. The brightness of Soorya (Sun) is more than that of Som (Moon), Moon is brighter than Mars and so on, thus the brightness get reduced further down. Saturn's brightness is the lowest among the 7 Graha. Hence, the days are arranged in accordance with their brightness from Sunday to Saturday. A Nava Graha Shlok is like this :
Sooryaaya, Somaaya, Mangalaaya, Budhayaashch,
Guru, Shukra, Shanibhyascha, Raahave, Ketave namah.

See the order of the Graha, it is not arrange as per anyone's wish. It is therefore proved, we only talk what Veda said, and nothing new.

(3) Nakshatra (Constellation) -
There are 27 constellations :-
1. Ashwinee,                2. Bharanee,              3. Krittikaa,         4. Rohinee,                     5. Mrigshiraa                   6. Aardraa,               7. Punarvasu 
8. Pushya,                  9. Aashleshaa,           10. Maghaa,          11. Poorvaa Phaalgunee      12. Uttaraa Phaalgunee     13. Hast,                   14. Chitraa          
15. Swaati                16. Vishaakhaa          17. Anuraadhaa      18. Jyeshthaa                 19. Mool                          20. Poorv Aashaadh    21. Uttar Aashaadh
22. Abhijit,              23. Shravan,              24. Dhanishthaa,    25. Shatbhishaa             26. Poorv Bhadraa,           27. Uttar Bhadraa,     28. Revatee

(4) Yog (combination) -
In Indian astrology, Yog is a part of Panchaang. There are 27 Yog in number and come through out the month in a specific sequence. They are like Nakshatra which also come throughout the month in a specific sequence. Since there are about 29-30 days in a month, one Yog is a little more of a day. Their names are as follows -

(1) Shubh,        (2) Shukla,          (3) Brahm,            (4) Indra,           (5) Vaidhritti,      (6) Vishkumbh,    (7) Preeti,    (8) Aayushmaan,   (9) Saubhaagya,  
(10) Shobhan,   (11) Atigand,       (12) Sukarmaa,      (13) Dhriti,         (14) Shool,           (15) Gand,           (16) Vriddhi,  (17) Dhruv,         (18) Vyaaghaat,  
(19) Harshan,   (20) Vajra,          (20) Siddhi,         (21) Vyateepaat,   (22) Vareeyaan,    (23) Prigh,         (24) Shiv,       (26) Siddh,         (27) Sadya.

(5) Karan -
[Taken from a write-up by a KP astrologer Uma Shankar Achanta]
Astrology says that a Yog is formed by the combination of 2 Karan, thus a Karan is made from half Yog. In total there are 11 Karan.

(1) Bav Karan
People born in this Karan are religious and like to be involved in sacred tasks. They are honest and believe in giving their best to any work that’s assigned to them. They keep their distance from illegal and impious activities. They have a sharp brain and are firmly grounded to reality. That’s why do not take flights of fancy. They are respected and loved for their qualities by everybody.
(2) Baalav Karan
Like the previous Karan this also gives a religious nature to the native. Persons born in this Karana may do pilgrimage and spend a large part of their life doing religious activities. They are well-educated and lead a very successful life.
(3) Kaulav Karan
Person born in this Karana are very sociable. This Karan gives its natives some of the finest qualities like love and caring. Their friends circle is really very big and the native usually gets favors from his or her friends. These people have a very strong self-esteem and no matters what happens they do not bow down before others.
(4) Taitil Karan
People born in this Karan are very fortunate. They have an affluent life and become an owner of buildings and assets. Love has a vital role in their life and perhaps this is the reason they treat people impartially.
(5) Gar Karan
Astrology says that native of Gar Karan are hard working. They believe in their ability not fate. They achieve their desired objective by hard work and labor. People of this Karan are proficient in agricultural and domestic works.
(6) Vanij Karan
Natives of this Karan are intelligent. It is seen that they have a keen interest in business and take this vocation for earning livelihood. They love to travel and may have to travel a lot for business purposes. Their intelligence is basically business oriented.
(7) Vishti Karan (Bhadraa Karan)
In astrology the Vishti Karan is not considered auspicious. This Karan cast its malefic nature on the native due to which the native might have a suspicious character. They may engage in immoral activities. The striking quality of the natives of this Karan is that they can go to the extreme to take revenge on their enemy.
(8) Shakuni Karn
Natives of this Karan are the followers of law and justice. They are very prudent in resolving conflicts. That means they can be very proficient in dismissing a quarrel with their intelligence. They take interest in medicine and may become a doctor or a physician.
(9) Chatushpad Karan
This Karana imparts religious inclinations to its natives. People born in this Karana respect learned people and serve animals. They are normally very fond of animals and know how to treat animals with medicine. They can become successful veterinary doctors.
(10) Naag Karan
Astrology regards this Karan as an inauspicious one. People born in this Karan may have unfortunate incidents. Their life may be full of conflicts and difficulties. They will get results only through hard work and effort, and not through luck. People of Naag Karan are usually very impatient.
(11) Kimstughna Karan
Natives of this Karan are very fortunate. They aggressively pursue humanitarian work. They will get every type of happiness in their life. They also receive quality education and lead a prosperous life.