How Our Calculations Work

Transparency matters. Here is exactly how Rasi & Rise computes planetary positions, daily timings, birth charts, and compatibility scores.

Astronomical Data

Every calculation on this site starts with real astronomy. Planetary positions are not pulled from pre-made lookup tables or simplified approximations. Instead, we compute the longitude of each celestial body - the Sun, Moon, Mars, Mercury, Jupiter, Venus, and Saturn - using established ephemeris algorithms that model their actual orbits.

We also calculate the positions of Rahu and Ketu, the north and south lunar nodes. These are not physical planets but mathematical points where the Moon's orbital plane crosses the ecliptic (the Sun's apparent path). In Vedic astrology, they carry the same weight as any visible planet and are essential for accurate chart interpretation. Their positions are derived from the geometry of the Moon's orbit relative to the Earth-Sun plane.

This approach means our data reflects what is actually happening in the sky at any given moment, not a static table that might be rounded or outdated.

The Sidereal Zodiac

There are two zodiac systems in use today. Western astrology uses the tropical zodiac, which is tied to the seasons. The first day of spring is always 0° Aries, regardless of which constellation is actually behind the Sun.

Vedic astrology uses the sidereal zodiac, which is aligned to the real positions of the stars. Because Earth's axis wobbles slowly over a roughly 26,000-year cycle (a phenomenon called precession of the equinoxes), the tropical and sidereal zodiacs have gradually drifted apart. Today, that drift is about 24 degrees, nearly a full zodiac sign.

To correct for this drift, we apply the Lahiri ayanamsa, which is the most widely used correction value in Indian astrology and the one officially adopted by the Indian government's calendar reform committee. The ayanamsa is subtracted from tropical longitudes to produce sidereal positions. This is why your Vedic sign is often one sign earlier than your Western sign - it reflects where the planets actually sit against the backdrop of the constellations.

Birth Chart Calculation

When you generate a birth chart, the system performs several steps in sequence. First, it converts your birth date, time, and timezone into a precise astronomical timestamp. Then it computes the tropical longitude of every planet at that exact moment. These tropical positions are converted to sidereal positions by applying the Lahiri ayanamsa for your birth year.

Each planet's sidereal longitude determines which of the 12 Rasis (zodiac signs) and which of the 27 Nakshatras (lunar mansions) it occupies. The Moon's position is especially important, as it defines your Rasi (Moon sign) and Nakshatra (birth star), the two most fundamental elements of your Vedic identity.

The Lagna (ascendant, or rising sign) is calculated separately. It depends on the local sidereal time at your birth location, which is a function of both the universal time and your geographic longitude. The Lagna changes approximately every two hours, which is why an accurate birth time is so critical. A difference of even 15 to 30 minutes can shift the Lagna to a different sign, changing the entire house structure of the chart.

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Panchangam (Daily Timings)

The Panchangam is the traditional Tamil almanac that maps each day's astrological qualities. Our daily timings calculations begin with computing sunrise and sunset for your specific geographic coordinates, using standard solar position algorithms that account for your latitude, longitude, and the date.

The daylight period between sunrise and sunset is divided into 8 equal segments. Three of these segments are assigned special significance based on the day of the week:

Rahu Kalam - a period considered inauspicious for starting new activities. It falls on a different segment each day (for example, the 8th segment on Monday, the 2nd on Tuesday, and so on).
Yamagandam - another inauspicious window, assigned to a different segment than Rahu Kalam for each day of the week.
Gulikai Kalam - a third period with its own weekday-based rotation.

The assignment of segments to days follows a fixed traditional pattern that has been consistent across Tamil almanacs for centuries.

Beyond the timing windows, the Panchangam also includes the five daily elements (the "pancha anga" or five limbs). Tithi is determined by the angular distance between the Sun and Moon, with each Tithi spanning 12 degrees of separation. Nakshatra is the lunar mansion the Moon currently occupies. Yogam is calculated from the combined longitudes of the Sun and Moon. Karanam is half a Tithi. Each of these is computed from real-time planetary positions, not looked up from a fixed calendar.

Muhurtham (Date Scoring)

When you search for auspicious dates, the system evaluates each candidate date across multiple criteria drawn from traditional Muhurtham rules. The factors considered include:

Nakshatra - which lunar mansion the Moon occupies on that date. Certain Nakshatras are considered favorable for specific types of events (weddings, travel, business) and unfavorable for others.
Tithi - the lunar day. Some Tithis are broadly auspicious, while others are avoided for important undertakings.
Day of the week - each weekday is ruled by a different planet, making it more or less suitable for certain activities.
Yogam - the Sun-Moon combination for the day. There are 27 Yogams, each with a traditional quality rating.
Karanam - the half-Tithi division, which adds another layer of filtering.

Different event types weight these criteria differently. A wedding date, for example, places heavy emphasis on the Nakshatra and Tithi, while a date for starting a business journey might prioritize the day of the week and the ruling Yogam. The system produces a composite score that reflects how well a given date aligns with the traditional rules for your chosen event type.

Porutham (Compatibility)

The 10-point Porutham system is the traditional Tamil method for evaluating compatibility between two people, most commonly used for marriage matching. Each of the 10 points examines a specific dimension of compatibility by comparing the two individuals' birth charts, primarily their Nakshatra and Rasi positions.

The ten matches include Dina Porutham (temperament), Gana Porutham (character type), Mahendra Porutham (well-being), Stree Deergha Porutham (prosperity), Yoni Porutham (physical compatibility), Rasi Porutham (emotional harmony), Rasiyathipathi Porutham (planetary ruler compatibility), Vasya Porutham (mutual attraction), Rajju Porutham (marriage longevity), and Vedha Porutham (obstacles).

Each point follows a specific set of matching rules. For example, Dina Porutham counts the Nakshatras from the bride's star to the groom's star and checks whether the result falls into a favorable division. Rasi Porutham evaluates the relative positions of the two Moon signs. These rules follow the traditional Tamil interpretation as practiced in Tamil Nadu.

The system reports which of the 10 points match and which do not, along with an overall score. Traditionally, a higher score suggests stronger compatibility, though individual points like Rajju and Vedha are sometimes given extra importance.

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Limitations and Honest Caveats

No system is perfect, and we believe in being upfront about where ours has constraints.

Birth time accuracy. All chart calculations depend heavily on the accuracy of the birth time you provide. A difference of a few minutes can shift the Nakshatra Padam, and a difference of 15 to 30 minutes can change the Lagna entirely. If your birth time is approximate, the chart should be understood as approximate too.

Birth location and timezones. Timezone handling is one of the trickiest parts of astronomical calculation. Historical timezone boundaries have shifted many times, and some regions have observed daylight saving time inconsistently. We use standard timezone databases, but for births in regions with complex timezone histories, small errors are possible.

One interpretation among many. Tamil Vedic astrology is a living tradition with regional variations. Different astrologers and different regions of Tamil Nadu may apply slightly different rules for Porutham matching, Muhurtham scoring, or even the fine details of Panchangam calculation. Our system implements one well-established interpretation of these traditional rules, but it is not the only valid approach.

Astrology as cultural tradition. We present these calculations as a faithful implementation of a centuries-old cultural and spiritual framework. We do not claim that astrological calculations can predict the future or replace professional advice of any kind. The value lies in connecting with a tradition that has shaped Tamil life for generations.