Chart angles
Angles are the fast-moving sensitive points tied to Earth rotation at the birth place. They are usually the Ascendant–Descendant axis and the Midheaven–IC axis.
The four angles
| Angle | Abbrev. | Astronomical idea |
|---|---|---|
| Ascendant | ASC | Eastern horizon ∩ ecliptic (rising degree) |
| Descendant | DSC | Western horizon ∩ ecliptic (opposition to ASC, +180°) |
| Midheaven | MC | Upper meridian ∩ ecliptic (culmination above horizon) |
| Imum Coeli | IC | Lower meridian ∩ ecliptic (nadir, opposition to MC, +180°) |
In astrorust_core, these appear in house cusp maps as Cross::Asc, Cross::Mc, etc., alongside numbered house cusps.
Dependence on birth data
Angles require UTC instant + latitude + longitude. A few minutes of clock error can change the Ascendant sign at many latitudes (birth-time-accuracy). Planetary VSOP longitudes can still be computed without precise time, but angles cannot.
House system coupling
- Placidus — MC is the 10th house cusp; ASC is the 1st cusp.
- Whole Sign — angles are still computed, but house topics follow whole signs; MC may not equal 10th cusp (house-systems-comparison).
- Equal — ASC degree starts equal 30° houses; MC floats (house-systems-comparison).
Sidereal charts
Under calculate_sidereal, angle longitudes are shifted by the same ayanamsa as planets when the ephemeris applies sidereal mode to cusps.
References
See also chart-points, houses, ecliptic-longitude.