Venus (Planet)
The second planet from the Sun — Earth's nearest neighbour by orbit but, in character, its most alien twin. Third brightest object in Earth's sky after Sun and Moon (magnitude −4.92), bright enough to cast shadows. Mythological counterpart: myth-aphrodite. Crossing note: crossing-venus-aphrodite.
Key Properties
| Property | Value |
|---|---|
| Orbital period | 224.7 days |
| Sidereal day | 243 Earth days (longer than its year) |
| Max elongation from Sun | ~47° |
| Orbital eccentricity | <0.01 (nearly circular — most circular of all planets) |
| Rotation | Retrograde — clockwise, opposite to most planets |
| Surface | Sun rises in the west, sets in the east |
The Retrograde Rotation Problem
Venus is the only planet (besides Uranus) that rotates retrograde — backwards relative to its orbit. Its day (243 Earth days) is longer than its year (224.7 days). This means on Venus: a single solar day is ~116.75 Earth days; a Venusian year contains only ~1.92 solar days. The cause is likely tidal locking to the Sun's gravity interacting with its dense atmosphere, over billions of years.
The Morning/Evening Star Discovery
Because Venus never strays more than ~47° from the Sun, it only appears around dawn or dusk. The Greeks initially believed it was two different stars: Phosphorus (*light-bringer*) in the morning and Hesperus (*western one*) in the evening. Pliny credits Pythagoras (6th century BC) with realising they were one object; Diogenes Laërtius credits Parmenides (early 5th century BC).
Critically: the Babylonians had already known this by the first millennium BC. The *Venus Tablet of Ammisaduqa* (possibly 2nd millennium BC) records systematic observations. The Sumerians (Inanna/Ishtar) may have known even earlier.
The Romans continued using both Latin names: Lucifer (morning — "light-bearer") and Vesper (evening) — literal translations of the Greek. This is why Lucifer appears in early Christian texts meaning the morning star (Venus), not a devil.
Cross-Cultural Naming
The identification of Venus as beauty/love/desire crosses cultures independently:
- Babylonian: Ishtar/Inanna — love and war goddess; Venus tablet named for her
- Egyptian: associated with Osiris, then Horus, then Hathor/Aphrodite
- Sumerian: Inanna — whose myth of descent and return mirrors Venus's disappearance/reappearance
- Sanskrit: *Shukra* — brightness, purity; rules Friday (*Shukravara*)
- Norse: associated with Frigg/Freya — "Friday" = Venus's day in all Romance languages
The 8-Year Cycle
Venus's orbital period creates a near-perfect 8-year resonance with Earth: Venus completes 13 orbits in 7.998 Earth years, so its sky position nearly repeats every 8 years. Ancient calendars across Mesoamerica and the Mediterranean tracked this cycle.