Angles and Houses

Using swe.houses()

Let’s calculate the house cusps and angles of a given chart. We’ll use the Swiss Ephemeris’ initial release in this example and the subsequent Printing a Chart tutorial with the following birth data:

  • 1997 September 30

  • 4:00 p.m. CEST (UTC+2) -> 14:00 UTC

  • Zollikon, Switzerland -> 47.33 N, 8.58 E[1]

For ease, we’re working with UTC so we can use the Python standard library datetime with swe.utc_to_jd(), but you can also use swe.utc_time_zone(). The merits of either are discussed in Time Zones and Julian Day Conversions.

As this is geocentric information that relies on coordinates, you’ll need to get into the habit of using coordinates as decimal degrees (DD) where negative latitudes mean the southern hemisphere and negative longitudes fall west of the prime meridian.

import swisseph as swe
from datetime import datetime, timezone

# 1. Define a day and convert it to Julian day (JD)
date = datetime(1997, 9, 30, 14, 0, 0, tzinfo=timezone.utc)
jd_ut, jd_tt = swe.utc_to_jd(
    date.year,
    date.month,
    date.day,
    date.hour,
    date.minute,
    date.second + date.microsecond / 1000000.0
    )

# 2. Define coordinates
lat, lng = (47.33, 8.58)

# 3. Calculate house cusps and angles
# b'P' selects hsys (house system) Placidus
cusps, ascmc = swe.houses(jd_tt, lat, lng, b'P')

# 4. Format and Print results
# Format each of the first 12 cusps to two decimal places and join them with a comma
formatted_cusps = ", ".join([f"{c:.2f}" for c in cusps[1:]])
# cusps[1:] slices off empty index 0, equivalent to cusps[1:13]

print(f"House cusps (Placidus): [{formatted_cusps}]")
print(f"Ascendant: {ascmc[0]:.2f}")
print(f"Midheaven: {ascmc[1]:.2f}")

# Output:
# House cusps (Placidus): [290.44, 341.06, 22.92, 50.38, 70.82, 89.30, 110.44, 161.06, 202.92, 230.38, 250.82, 269.30]
# Ascendant: 290.44
# Midheaven: 230.38

Explanation

The most reliable way to access the angles (Ascendant and Midheaven) is to use the dedicated ascmc tuple..

Tuple name

Length

Contents

cusps

13 or 37

Cusps for the 12 houses or 36 Gauquelin sectors where index 0 is empty.

ascmc

8

Ascendant, Midheaven, Vertex, Equatorial Ascendant, etc.

Accessing angles

  • The Ascendant (ASC): Always at value ascmc[0].

  • The Midheaven (MC): Always at value ascmc[1].

In quadrant house systems like Placidus (used in this example), Campanus, Regiomonatus, or Koch:

  • ascmc[0] (AC) should be the same as cusps[1] (1st house).

  • ascmc[1] (MC) may be theoretically the same as cusps[10] (10th house).

It’s generally best practice to still use the ascmc tuple for the Ascendant and Midheaven, which lie between two cusps in whole sign houses and some equal house systems

Other house functions

Besides swe.houses(), pysweph also offers: