Cosmea Astrology for Two

Synastry calculator (no partner birth time needed)

Enter two birth dates and, when known, times. You get the tight cross-chart contacts (within 2 degrees) and a 14-day preview of green, amber and red days for the pair, computed in your browser from the real sky. If a birth time is unknown, the Moon is labelled uncertain rather than guessed.

Positions come from an ephemeris that matches Swiss Ephemeris within 0.01 degree on a 200-chart test set (1936 to 2026).

You
Them

You are entering another person's birth details. They stay in this browser only. We never upload, store or see them. Only use details you are entitled to use.

Web preview fidelity: no birth place, so no Ascendant, Descendant or houses; no void-of-course Moon; no eclipses; no progressed Moon. The app scores all of these on the device.

Astrological weather, not a forecast. The dates are computed from both charts against the real sky; the colours are interpretation, not prediction. Green means the astrology traditionally favours connection, red means it traditionally favours patience. Not advice about any real person's feelings or choices.

The dates are computed from both birth charts against the real sky. The colours are astrological interpretation, not prediction: green means the astrology traditionally favours connection, red means it traditionally favours patience. Controlled studies have not shown astrology predicts events. Use this as a lens for timing conversations, not as advice about a person or a decision.

See your green and red dates for 90 days: join the waitlist for the app.

Get your 90-day calendar when Cosmea opens

Cosmea is in the works. Join the waitlist and be first to see your green and red dates for you two, computed from both charts.

Email only. No birth data is sent with this form; the calculator runs in your browser and nothing you type there leaves it.

FAQ

How does a synastry calculator work without a birth time?

Planets other than the Moon move less than about 1 degree in a day, so the date alone places them. The Moon moves about 14 degrees a day, so a noon chart carries a 7-degree uncertainty. This calculator shows that uncertainty, scores Moon contacts at half weight, and does not compute houses or angles for that person.

What counts as a tight contact?

A conjunction, sextile, square, trine or opposition between a planet in one chart and a planet in the other, within 2 degrees, where at least one of the two is the Sun, Moon, Mercury, Venus, Mars or the lunar node.

What do the colours mean?

Each day is scored from transits to both charts, to the tight contacts and to the composite (midpoint) chart, using conventional weights from the practitioner literature. Green is a score of +4 or more, red is -3 or less, amber is in between. Venus station days are red for new commitments whatever the score.

Is my data uploaded?

No. The charts are computed in your browser by the same ephemeris the app uses. This page sets no cookies and runs no analytics.