Jyotish or Jyotisa also known as Vedic Astrology is one of the Vedānga, the six auxiliary disciplines used to support Vedic rituals. The foundation of Hindu astrology is the connection to Vedas, (scriptures), which is the connection between the microcosm and the macrocosm. Jyotisa relies primarily on the sidereal zodiac, which is different from the tropical zodiac used in Western (Hellenistic) astrology in that an ayanānśa adjustment is made for the gradual precession of the vernal equinox. (more technical details will be in the article section shortly). Hindu astrology includes several nuanced sub-systems of interpretation and prediction with elements not found in Hellenistic astrology, such as its system of lunar mansions (Nakshatra).

The ancient Indian astrology or more popularly called ‘Eastern’, ‘Sidereal’ astrology is technically Vedic astrology.  More technically it is known as Jyotisha.

Jyotiṣa is composed of two words.  Jyotis + ṣa. Jyotis means light/brightness/an illuminating object whereas ṣa means mastery. The mastery of the lord of the light is what is Jyotisha. Now the one who is the master of light has to study this light and so a Jyotishi is one who studies the light. Hence a Jyotisha also means the study of light.  Jyoti means light and Isha means the study.

For this, you have to understand the building blocks of Hindu or Sanatana dharma.  Take a look at the following diagram and try and get your head around it!