Retrograde
glossary.
The words used on every Cazimi page, each defined once: stations, shadows, conjunctions and the coordinates they are measured in. The dates themselves come from the JPL DE421 ephemeris, in UTC to the minute.
- Retrograde motion
- The stretch of time when a planet, seen from Earth, moves westward against the background stars instead of eastward. The planet never reverses in its orbit; the backward drift is an effect of Earth overtaking it, or of it overtaking Earth. What is Mercury retrograde.
- Station retrograde
- The minute a planet's apparent motion along the ecliptic slows to zero and turns backward. Cazimi times it as the minute the planet's geocentric ecliptic longitude stops increasing. How stations are timed.
- Station direct
- The minute a retrograde planet's apparent motion slows to zero and turns forward again. The retrograde period runs from station retrograde to station direct.
- Pre-shadow
- The weeks before a retrograde when the planet, still moving forward, crosses the degrees it will later retrace. It starts when the planet first reaches the degree where it will station direct. Mercury retrograde shadow period.
- Post-shadow
- The weeks after a retrograde when the planet moves forward over the same degrees again. It ends when the planet passes the degree where it stationed retrograde.
- Inferior conjunction
- The moment Mercury or Venus passes between Earth and the Sun, so that its ecliptic longitude equals the Sun's. It falls in the middle of every Mercury and Venus retrograde.
- Superior conjunction
- The moment Mercury or Venus lines up with the Sun on the far side of it from Earth. It falls in the middle of the direct phase, between two retrogrades.
- Cazimi
- A traditional astrology term for a planet in the heart of the Sun: within 17 arcminutes of the Sun's centre in longitude. For Mercury it happens at inferior conjunction, inside the retrograde, and lasts a few hours. Every Mercury cazimi with its window.
- Combust
- A traditional astrology term for a planet close enough to the Sun to be hidden by its glare, usually within about 8°30′ of longitude. Cazimi is the narrow centre of that zone; the rest of it is combust.
- Opposition
- The moment an outer planet, from Mars to Pluto, stands opposite the Sun as seen from Earth. It falls in the middle of the outer planet's retrograde, when the planet is closest and brightest. Mars retrograde.
- Ecliptic
- The Sun's apparent yearly path across the sky, which is also the plane of Earth's orbit. Zodiac signs are 30° slices of the ecliptic counted from the March equinox.
- Ecliptic longitude
- A position along the ecliptic in degrees, from 0° Aries to 360°. Cazimi writes it as a degree within a sign, such as 5°59′ Pisces, and uses the apparent geocentric value.
- Apparent geocentric position
- Where a planet appears from the centre of Earth, corrected for the time its light takes to reach us. Retrograde motion only exists in this Earth-centred view.
- Ephemeris
- A table or model that gives the positions of the Sun, Moon and planets at any moment. Cazimi uses NASA JPL's DE421 planetary ephemeris through the Skyfield library. JPL planetary ephemerides.
- JPL Horizons
- NASA Jet Propulsion Laboratory's online service for solar system positions. Cazimi's station and cazimi times were checked against it to the minute. The Horizons check.
- UTC
- Coordinated Universal Time, the time zone-free clock every Cazimi time is given in. Your local time is UTC plus your zone's offset, which is why a station can fall on different calendar days in different countries.
Questions
What is the difference between cazimi and combust?
Combust is the wide zone, about 8°30′ either side of the Sun, where a planet is hidden in its glare. Cazimi is its narrow centre, within 17′ of the Sun’s centre; the next Mercury cazimi is February 18, 2027 at 16:39 UTC.
What is a station retrograde?
The minute a planet’s apparent motion against the stars stops and turns backward, as seen from Earth. Mercury’s next station retrograde is February 9, 2027 at 17:36 UTC, and its station direct March 3, 2027 at 12:32 UTC.
What is the ecliptic?
The Sun’s apparent yearly path across the sky, along which planet positions are measured as ecliptic longitude. Mercury stations retrograde February 9, 2027 at 17:36 UTC, at 5°59′ Pisces of ecliptic longitude.