There are a many differences between what is known as Western astrology and Jyotiṣa, or Vedic astrology. Some major ones are:
First and foremost, Jyotiṣa is based on the sidereal zodiac. A planet’s position in the heavens is measured against the backdrop of fixed constellations in the sky. Western astrology, instead, uses what is known as the tropical zodiac, which is based upon the seasons and fixes the beginning of Aries at the time of the vernal equinox. While these two measurements coincided more than 2,000 years ago, a difference in measurement has accrued of about 24 degrees. This difference is caused by a phenomena called the ‘precession of the equinoxes’, which makes it so that the point of the vernal equinox drifts back imperceptibly in relation to the fixed stars. This is due to the earth’s slight bulge, and hence constant wobbling to remain balanced, That means that in most cases, your “sun sign” in Jyotiṣa is one zodiacal sign behind your western sun sign.
Because Jyotiṣa existed thousands of years before the invention of the telescope, it charts those sky objects that were visible to the naked eye. This includes the 5 true planets (Jupiter, Venus, Mercury, Mars and Saturn), the two luminaries (Sun and Moon) and the Moon’s nodes Rahu and Ketu, which are accorded the status of planets. Western astrology also includes other planets and asteroids.
Jyotiṣa is furthermore in a unique and privileged position in its integration of solar and lunar astrologies. It is known for its vibrant use of nakṣatras, or lunar constellations. Nakṣatras, also known as the Moon’s brides, allow for a profoundly eternal and real connection with permanent themes of the Universe, and how those themes express individually in a natal chart. Nakṣatras are also heavily used in electional astrology to select auspicious times to commence activities.
Jyotiṣa has the ability to fine-tune chart analysis through the use of sub-charts known as āmśas. Āmśas help glean further insight into specific areas of one’s life such as relationships, money and success, health, children, parents, challenges, etc, and allow specific timing of events in those areas of life.
One of Jyotiṣa’s greatest strengths is the ability to time planetary periods. Based on the Moon’s position at birth, it is possible to identify what planets are going to be most active at any given point in time. This enables to see what karmas are fructifying when, and that is how we learn to dance with the rhythms life presents us. While all the planets can be considered the actors in the play, at any given moment in time only one planet is the main actor (daśā) in the spotlight, accompanied by secondary actors (bhuktis).
The knowledge of what is activated in a chart by dasha, or planetary period, is then combined with the information of transits, or what the current motion of planets in the sky is relative to the original birth chart. While Western astrology also works with transit, it does not have the information of what is activated by daśās and bhuktis.
While Western astrology tends to focus on a psychological understanding of one’s life, Jyotiṣa ventures into all of life’s areas of interest, from the mundane to the sublime. The perspective offered is further contextualized by a profound understanding of karma and how it manifests in a chart. Jyotiṣa is not fatalistic, but it does indicate which tendencies and areas of our life are easier to change, which ones require a more dedicated effort to alter, and which karmas are strongest and hence it is best to understand deeply and integrate.