The Ascendant is the ecliptic degree rising on the eastern horizon at the
given moment and location. It's the cusp of the 1st house in most house systems.
Formula from Meeus:
tan(ASC) = cos(LST) / -(sin(ε) * tan(φ) + cos(ε) * sin(LST))
where:
LST = Local Sidereal Time
ε = obliquity of the ecliptic
φ = geographic latitude
Parameters
lst: number
Local Sidereal Time in degrees (0-360)
obliquity: number
Obliquity of the ecliptic in degrees (~23.4°)
latitude: number
Geographic latitude in degrees (-90 to +90)
Returns number
Ascendant position in ecliptic longitude (0-360°)
Throws
If latitude is at exact poles (±90°) where ASC is undefined
See
"Astronomical Algorithms" by Jean Meeus, Chapter 13
Example
// London: lat = 51.5°, LST = 180°, obliquity = 23.44° constasc = calculateAscendant(180, 23.44, 51.5); console.log(asc); // Ecliptic degree rising at this moment
Calculate the Ascendant (ASC)
The Ascendant is the ecliptic degree rising on the eastern horizon at the given moment and location. It's the cusp of the 1st house in most house systems.
Formula from Meeus: tan(ASC) = cos(LST) / -(sin(ε) * tan(φ) + cos(ε) * sin(LST))
where: