What these points are
A lot is a calculated zodiac position, not another planet. Fortune starts with the Ascendant and projects the arc between the Sun and Moon from it. Spirit uses the complementary arc. In a day chart the site computes Fortune as Ascendant + Moon − Sun and Spirit as Ascendant + Sun − Moon. In a night chart the formulas reverse. Each result is wrapped into the 0–360° zodiac.
The automatic day/night choice uses the Sun's geometric altitude at your entered place and instant. At the horizon, a few minutes of birth-time uncertainty or atmospheric refraction can reverse the choice. The manual selector lets you compare both conventions transparently; it does not correct a missing birth record. The calculator labels the points by Whole Sign house to aid chart reading, although the lots themselves do not depend on a house system.
Traditions differ about additional lots, allowable sect conventions, and interpretation. This tool calculates two named lots only. It does not reproduce a larger catalogue of lots or generate a fate prediction.
References
- Al-Biruni, Book of Instruction, verse 476, Wright translation; annotated table - traditional lots formulas and night reversals.
- Digital facsimile of Al-Biruni’s Book of Instruction - context for the eleventh-century work and the 1934 translation.
- Astronomy Engine documentation and source - the astronomical library used for planetary positions and the local horizon calculation.
These sources describe a historical method and the astronomical implementation. The site calculates positions independently with Astronomy Engine 2.1.19 and its own birth-chart code.