Some complementary readings for Jyotish studies
Itihaasa
Ramayana and Mahabharata are called ithihaasa meaning history. The Etymology of the word could possibly be derived  in sanskrit  thus,

itihaasa is iti+haasa; iti means thus and haasa means humorous/entertaining anecdote.

These are books attempting to document various turning points in history to reach a moral conclusion. Moral conclusion being the main theme and documentation secondary. These sequence of stories makes reader associate with certain characters in the story and help reader reach a certain level of psychological development. My belief is that these books are not specific to any religion, but a general torch light for seekers of answers for many queries in life. Person can read this in conjunction with whatever belief one has built up so far.
Ramayana.
Ramayana was re-written/translated by many authors or seers Like Valmiki, Kambar, Tulsidas etc being some famous ones. The First being Valmiki, Who is called the First Poet for his developement of Chandas.
A very good site with lot of resources on Ramayana is
                          
http://www.ValmikiRamayan.Net
The same site has links to other site with stories on Ramayana.
Mahabhaaratha.
This book has total 18 parvans(sections for english translations of some of them you can refer the following web site.
http://www.yorku.ca/inpar/Sanskrit.html
Puranas
Purana means old pre-historic stories. These contain stories attempting explain whole cosmos with it's laws, creation and dissolution  etc. These books may contain historic fact or allegorical stories attempting to explain a concept. Some stories should not be taken literally they should mapped to certain ideas to derive the meanings.The purana's themselves contain the explanations to understand such stories.
For a brief introduction of all major (18 major and many minor ones) purana are
http://www.gita-society.com/temple/HinduPuranas16.htm
Vedas
It's told that vedas cannot be understood without reading Six Vedangas, Mahabharatha, Ramayana and the major purana's. They form the basic foundations for understanding the vedas. Sri Aurobindo is one of few modern teachers who was able to give some meaning of the veda's. He is sometimes called the Shankaracharya of modern times.
This website contain some very good literature on the same.
http://www.vedah.com/index.htm
Upanishads.
Upanishads are called vedanta or literally end of veda's meaning they give you the conclusions. These are mostly shlokas contained at the end of Vedas. Bhagavat Geeta is one of the principle upanishads, But instead of Vedas it appears in Mahabharata, Hence Mahabharata is also sometimes called the 5th Veda . To get proper conclusion of Vedas one should read Upanishads in conjunction with the ithihaasa.
You can search for many Geeta sites in the internet. The Geeta as we have it today was given by Adi Shankaracharya when certain verses were lost.
You can refer to text of the Geeta at http://www.asitis.com/
This site also has commentaries by Srila Prabhupada. Other commentaries which should be read are of Adi Shankaracharya, Ramanuja etc
You can begin your journey in quest for ancient knowledge in sanskrit by reading various texts in http://sanskrit.gde.to
Before you start Jyotish Studies it's recommended that you read atleast Mahabharata and Geeta.
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