The Rose of Venus
This is the path Venus traces around the Earth, day by day, for eight years. It loops back on itself five times, once at each of its meetings with the Sun, and then returns almost exactly to where it began. Join those five meetings around the zodiac and they draw a pentagram.
| One rose | 8 years |
|---|---|
| Petals and conjunctions | 5 |
| Synodic period | 583.9 days |
| Star drifts back | About 2.3° per 8 years |
What you are looking at
The Earth sits at the centre and the sign wheel runs around the edge the way a birth chart does, with Aries on the left. The glowing line is Venus's position relative to the Earth, one point per day. When Venus swings around the far side of the Sun it makes the wide outer arcs, up to 1.74 AU away. When it passes between the Earth and the Sun it comes as close as 0.27 AU and makes one of the five small inner loops.
Those inner loops are Venus retrograde. From the Earth, Venus seems to stop, walk backwards against the stars for about six weeks, and turn forwards again. The gold points on the wheel mark the exact degree of each inferior conjunction, the moment in the middle of a retrograde when Venus lines up with the Sun.
The math
Venus and the Earth come back to the same alignment every 583.9 days, its synodic period. Five of those cycles take 2,919.6 days, which is within a couple of days of eight Earth years (2,921.9 days) and of thirteen Venus years (2,921.1 days). That near match of 8, 13 and 5 is why the pattern closes, and why the rose has five petals.
Each inferior conjunction falls about 216 degrees further around the zodiac than the last, which reads as about 144 degrees back. Join them in order and every step skips one point of a five-pointed star, so the chords draw a pentagram rather than a pentagon. Because five cycles fall 2.3 days short of eight years, each new star lands about 2.3 degrees behind the last one, and the whole figure turns slowly backwards through the zodiac. Choose a longer span to watch it turn. After 243 years, 152 conjunctions later, the pattern lines up again closely, which is the same rhythm that makes transits of Venus across the Sun repeat on a 243-year cycle.
How it is computed
Positions come from astronomy-engine, an open source ephemeris that agrees with the Swiss Ephemeris to well under an arcminute, running in your browser. The path is Venus's position minus the Earth's in a fixed frame, sampled every day (every two or three days for the longest spans), turned once so it lines up with the tropical zodiac on the start date.
The conjunctions are found by searching for the moment Venus and the Sun share the same apparent ecliptic longitude, to within about a minute, and the degree shown is the one an ephemeris would print for that moment. Nothing is approximated as a circle: the slight unevenness between petals is the real shape of both orbits.
Questions
Why does Venus draw a pentagram?
Venus meets the Sun from our point of view five times in almost exactly eight years, and each meeting falls about 144 degrees back around the zodiac from the last. Joining five points spaced like that in order draws a five-pointed star.
Is the Venus pentagram perfect?
Almost. Five Venus cycles take 2.3 days less than eight years, so each star lands about 2.3 degrees behind the previous one. Over about 1,250 years the star turns all the way around the zodiac.
What are the small loops near the Earth?
Each one is a Venus retrograde. Venus passes between the Earth and the Sun, appears to move backwards against the stars for about six weeks, and the path folds into a loop.
Can I see the rose from my birthday?
Yes. Set the start date to any day between 1700 and 2300, such as your birthday, and the piece draws Venus's path for the eight years after it, with the degrees of each conjunction on the wheel.