about
why two charts?
If you've ever felt your horoscope sign didn't quite fit, you may have looked up your "real" constellation and found a mismatch. That gap has a name: precession. stardrift shows both readings side by side so you can see exactly where they diverge.
the tropical zodiac
Modern Western astrology uses the tropical zodiac. Zero degrees Aries is anchored to the vernal equinox — the moment spring begins in the Northern Hemisphere — not to a particular group of stars. Signs are defined by seasons, which makes the system internally consistent even as the sky shifts.
This is the zodiac of newspaper horoscopes, most natal chart apps, and contemporary astrological practice in Europe and the Americas.
the sidereal zodiac
Mesopotamian astrologers (~2000 BCE) mapped planets against visible constellations. Their zodiac was sidereal — tied to fixed stars. When the system was first drawn, the two frames roughly aligned: the equinox sat near the beginning of the constellation Aries.
Four thousand years later, they no longer match. Earth's axis wobbles like a spinning top, completing one cycle in about 26,000 years. The effect: the equinox drifts westward through the constellations at roughly 50 arcseconds per year — about one degree every 72 years, or nearly a full sign every 2,160 years.
what stardrift calculates
Enter your birth place, date, and time. stardrift geocodes your location, computes planetary positions using the VSOP87 ephemeris (via Astronomy Engine), and renders two black-and-white chart wheels:
- Tropical — ecliptic longitudes of date, as Western astrology uses them today.
- Sidereal — the same longitudes adjusted by ayanamsa (~24° in the early 21st century) to reflect where planets sit against fixed stars.
We then compare placements sign by sign and highlight where readings would describe different temperaments for the same birth moment.
who this is for
Whether you're curious why your Sun sign "feels wrong," studying the history of astrology, or already fluent in ayanamsa and just want a clean comparison tool — stardrift is built to show the data without telling you what to believe.