Who made this
I'm sadalsvvd; nice to meet you. Cygnus is the culmination of eight years of deep study in astrology, and over a dozen years (a whole Jupiter cycle!) of professional experience building software for the web. I've had a lot of time to develop lots of opinions about what my dream astrology software should look and feel like. Keeping with its namesake of the swan, I want using Cygnus to feel like spreading your wings and flying.
Community and feedback
Cygnus is in early access. The fastest way to shape what it becomes is to use it, then tell me what's broken or missing. You can email me at sadalsvvd@cygnus.so, find me on Bluesky, or submit feedback on the Feedback page. If you'd like to help Cygnus become a success, tell your friends about it!
How it works
Cygnus runs on a custom ephemeris engine built on open-source astronomical science and formulas using NASA JPL astronomical data. The ephemeris handles astronomical necessities for geocentric observation of planets and layers on astrological concerns like house cusp calculation and zodiac construction.
For the technically inclined: Cygnus computes planetary positions from NASA JPL's DE-series development ephemerides (DE421/DE440), applies the IAU 2006 precession model (Capitaine et al. 2003) with the Vondrák, Capitaine & Wallace (2011) long-term extension for dates outside the central millennium, and the IAU 2000A/B nutation model (Mathews–Herring–Buffett 2002; IERS Conventions 2010, Chapter 5). Earth rotation — the ΔT term (TT − UT1) that ties civil time to the sky — is sourced from IERS Earth Orientation Parameters (the finals2000A.all bulletin) for the modern range, Stephenson, Morrison & Hohenkerk (2016/2020) cubic splines for 720 BC – AD 2025, and Espenak–Meeus polynomials at the extremes. House cusps follow the Munkasey formulary.
The IERS publishes updated Earth orientation tables several times a year; Cygnus ships with the latest bulletin available at release. Positions for very far future or very deep historical dates may shift slightly as fresh observations supersede the projections in use today. House cusp computations for some systems can show small discrepancies at extreme latitudes (above the Arctic Circle, below the Antarctic Circle); this is a known area of ongoing refinement.