HOW IT WORKS

Your stars.
A better conversation.

Us & Stars is a free birth-chart comparison tool for adults. This comparison is called synastry. We pair calculated planetary contacts with symbolic reflection prompts — a starting point for conversation, not a verdict on your relationship.

What details do I need?

Each person’s birth date, local birth time and time zone. A nickname is enough. Only use details you have permission to use. The standard report is calculated in your browser; the app does not send your birth details to a server or save them. Reloading clears the report.

What does the comparison show?

When both birth times are supplied, we compare seven celestial bodies, from the Sun to Saturn, and look for five kinds of angular contact, called aspects. You can see the measured positions, up to 12 selected contacts, and questions about communication, affection and boundaries. There is no compatibility score.

Where do the interpretations come from?

The standard report uses editorial templates linked to the calculated contacts, not AI-generated text. The sample is fictional, not a customer story. Astronomical positions are calculations; their astrological meanings are symbolic and are not a scientifically validated way to measure relationship quality.

What if I don’t know a birth time?

Choose the unknown-time option. We use noon as an approximate reference, omit that person’s Moon, and withhold all precise between-chart aspects if either time is unknown. You still get a limited view and general conversation questions. We never guess a birth time, rising sign or house.

See the fictional sample →Try your own comparison →

Calculation details and sources

We use Astronomy Engine 2.1.19 for geocentric tropical ecliptic longitudes of the Sun, Moon, Mercury, Venus, Mars, Jupiter and Saturn. Local times are converted through Luxon and your browser’s IANA time-zone data. Location only helps select a time zone; this tool does not calculate houses, angles or topocentric positions.

An orb is the distance from an exact aspect angle. Our limits are: conjunction (0°, 6° orb), sextile (60°, 4°), square (90°, 5°), trine (120°, 5°), and opposition (180°, 6°). We omit contacts where both bodies are Jupiter or Saturn. Up to 12 contacts are ordered by smallest orb, not relationship importance. Approximate signs near a boundary may change during the day.

We adapted uncertainty and non-fatalistic interpretation principles from the MIT-licensed astrology-skill project. Neither these principles nor the calculation library establish the scientific validity of astrological interpretations.

An optional owner-only AI test can send selected planet names, aspect types and orbs to DeepSeek, without names or birth details. It requires a separate explicit request. AI drafts are labeled and checked for chart references, but can still be misleading. This is not part of the standard report. See our privacy explanation.