Day or night is a calculation, not a date label
In the basic sect rule, a chart is diurnal when the Sun is above the local horizon and nocturnal when it is below. A clock hour alone cannot classify a chart, because sunrise and sunset vary with date, latitude, longitude, and historical civil-time rules. The calculator derives a UTC instant from the local birth record and stated UTC offset, computes the Sun’s topocentric geometric altitude, and chooses the corresponding formula. It shows the altitude and allows a manual branch for comparison.
At sunrise or sunset, a small error in the recorded time or birthplace can move the Sun across the horizon. Atmospheric refraction and conventions for the solar disk also affect what people call sunrise. The tool warns when its geometric altitude is within 0.5°. An unknown birth time cannot responsibly be replaced with noon: that changes the Ascendant and can also change sect. A wrong historical UTC offset shifts both the chart and the horizon calculation.
What reverses in this table
Al-Biruni distinguishes formulas that stay the same from those whose beginning and end are exchanged at night. His seven planetary entries belong to the reversing group. For Fortune, the day arc Moon − Sun becomes Sun − Moon at night. Spirit uses the complementary direction. The five added entries reverse the order of their two terms as shown in the source table. This does not imply that every lot in the much longer list reverses; some are explicitly marked the same in day and night births.
A source variant is more than a rounding difference
The latter is associated with the Hermetic lots transmitted by Paulus of Alexandria. One should not assume a shared label gives the same formula. Al-Biruni’s broader list also contains alternate formulas and conditional exceptions for some topics. The present tool intentionally confines itself to his seven planetary entries, where the source gives explicit day and night expressions. It does not silently select a formula for a different “Lot of Marriage,” “Lot of Children,” or “Lot of Necessity.”
Checking a disagreement step by step
- Confirm local birth date and time, birthplace coordinates, and the historical UTC offset. Different time-zone assumptions can change the Ascendant by many degrees.
- Check whether both charts use tropical longitudes and the same planetary positions and calculation date.
- Read the Sun’s altitude or sect determination, especially near the horizon.
- Compare the entire formula, including the casting point, added term, and subtracted term. A familiar name alone is insufficient.
- Compare the unrounded longitude before deciding that a one-minute difference is meaningful.
Whole Sign house numbers in the tool help locate a point in a chart. The lots’ actual longitudes do not depend on the chosen house system. Near geographic polar singularities, the Ascendant may be undefined and the calculator withholds a fabricated result.