Varaaha is Prakruti (nature), Mihira is the Jyotisha Sutra by which one can understand the effects of Khagola Kirana Paata on this nature. He mastered that sutra & was called as VaraahaMihira!
Varahamihira was from Vidarbha Pranthya. Did his graduate studies in astrology in his native and came to Kerala for post-graduate studies. Stayed in Tiruvanantapuram temple’s Archaka’s house. He started “Surya-Anushtana” there & got instruction in dreams to write a book on the properties of nature that could be understood by common men. He continued his Anustaana for 12 years. The rough collection of his studies, tests, results & implications due course of time was “Laghu Jaathaka”. It was a collective effort of studying the variations in light rays of 7 basic Grahas with respect to Hora. His research was carried out “AhoRatra” – day & night by casting horoscopes of each hora & several other light wave related practical experiments. Initially he prepared the “Bruhat-Samhita” explaining the properties of natural phenomenon. Then went on writing “Hora-Shastra” based on the core Bruhat-Jataka of Battotpala.
Varahamihira’s real works have an influence of Vidarb language & culture. The main 2 Granthaas were written in Malaya language in AaKhyaika style. AaKhyaaika is the method of narration of any subject matter in terms of stories, which are easily memorable. In those times there used to be Vidwat Parishat which scrutinizes any literature. Till 1722 A.D. we find the existence of these Vidwat Parishats. Long ago, there used to be Saptarshi-Parishat for accrediting the Granthas. However, we found no activity of Saptarshi-Parishat in this regards after ending of Kaushambi Vishwavidhyalaya. Since the work was in Malaya language, it was rejected by Vidwat-Parishat. Hence he rewrote them in Sanskrit and got accepted. The Varahamihira’s date may be 200-300 B.C. We have references of Yativarenya Annappa Swamy lived till 2,100 from now (2012). The attacks on Astrology & Astronomy of India started during 10th Century.
23 different people have written Bruhat-Samhita’s! The one which is available in stores is not the original work of Varahamihira, but a collection from different manuscripts covering vast area. 25 different Pancha-Siddhantika Grantha’s are there! It’s usually a collection (Samikarana) of any 5 Jyotisha Siddhantas. Very great Astronomical Scientists have formulated them. Varahamihira also contributed to Pancha-Siddhantika.
Shiva is said to be the Adya Pravartaka of Jyotisha. Shiva means Shubha, Mangala-Apeksha. The world sees in two-dimensional eyes. The third eye, which promotes extra visualization to see the Physical world, is known as Jyotisha. Therefore, Veda says “Jyotishaa Baadhate Tamaha”. Vedanga-Jyotisha purely concentrated on the “Kaala-Nirnaya”. Nearly 40,000 years ago “Lagadha” Maharshi formulated the present system of Vedanga-Jyotisha in 8,000 Shlokas. He says that Jyotisha is for performing Yagna-Yaagas, the fruitfulness of which will be welfare of whole society. In Yaagas, the accuracy of Mantra-Prayoga depends on the Khagola-Kirana, which in turn requires perfect time slice designed according to Mantra Kaala Nirnaya Sutras. In spite of all the steps of Vedanga-Jyotisha have been followed, if a mantra does not give results, then it says that there is a mistake in Mantra. So proceed towards Mantra Parishkarana. Therefore, Jyotisha is one of the six main parts of testing the Vedas.
E.g., Rishyashrunga was a great sage & was masters of Jyotisha. There was a small mistake in calculations of Jyotisha during Putrakamyesti Yaga. Dasharatha was in depression due to the Marana Shakunas he has experienced and was desperate to crown Rama. Sage Vasista was also expert in Jyotisha. Dasharatha ordered Sage Vasista to fix a muhurta for the next day for Rama’s Pattabishekam. This was not at all the way of asking a muhurtha according to rules of Jyotisha. The Daivajnatwa of Vasista didn't work when it was an order and as a Rajarshi he has to follow the same! Therefore, gets reasonably good Muhurtha from the day being fixed by Dasharatha. These incidents were one among the strong reasons, which made Rama to go Vanavaasa and the Simhasana of Surya-Vamsha vacant for 14 years!
Lagadha Maharshi says that everything is depends on Kaala. He started with the parts of time from Vedas, went lakh-fold deeper and said that the “Chaitanya-Taranga” between the Anu’s should be invented for Jyotisha. This is called as Anu-Niyaamaka Kaala, which is Ati-Sookshama & Ati-Spasta. The traces of which is being tried in terms of Atomic Clocks. But these modern clocks have lots of errors!