Learn

The questions people ask about birth charts.

We’ve answered each one plainly, with our own figures, as the people who built Mercury.

• Can AI read your birth chart? We tested it.We asked general AI models for 16 people’s charts and readings in four traditions and checked every claim. What they got right, what they got wrong, and why.
• Why is my Sun sign different in Vedic astrology?Vedic astrology measures the zodiac from the stars and Western astrology from the seasons, about 24° apart, so most people land a sign earlier. Here is why, and what else moves.
• What if I don’t know my birth time?Without a birth time you still have most of a chart. What changes during a day, what we show and withhold, and where to find the time.
• Placidus or whole sign: why do houses differ between apps?There is more than one way to divide a chart into twelve houses. What a house system does, how Placidus and whole sign differ, and which each tradition uses.
• What is a BaZi chart?BaZi reads a birth as four pillars, year, month, day and hour, each a heavenly stem and an earthly branch. How it works, why the year starts in February, and the clock question.
• How accurate is a birth chart?The planets are the easy part: within one arcsecond of NASA since 1900. What really makes a chart wrong is the birth time and the time zone it was recorded in.

Why your chart here may differ from another app’s

Two correct charts can disagree, because astrology is several traditions, and each makes choices. These are the ones that move things, and which way we went:

• The zodiac. Western and Hellenistic charts count from the seasons (tropical); Vedic counts from the stars (sidereal), with the Lahiri ayanamsa. Why that moves your signs.
• The houses. Placidus for Western, whole sign for Hellenistic and Vedic, none in BaZi. What the difference is.
• The birth clock. The time zone and daylight saving as they were that day, and a town’s own time before standard time. Why it matters more than the planets.
• BaZi’s clock. The clock on standard time with the sun’s time beside it, and the day turning at midnight, naming the other pillar wherever schools disagree. How BaZi works.
• No birth time. Local noon, with what noon can’t know left out. What you still get.

Every rule we follow, technique by technique, is written down. If you’re an astrologer comparing figures, ask us and we’ll send it.