General

A day on Venus is longer than a year on Venus.

📅February 1, 2026 at 1:00 AM

📚What You Will Learn

  • Why Venus day > year.
  • Difference between sidereal and solar days.
  • Causes of slow, backward spin.
  • How atmosphere affects rotation.
  • Implications for Venus's hellish climate.

📝Summary

Venus spins so slowly that one full rotation—a sidereal day—takes 243 Earth days, outlasting its 225-Earth-day orbit around the SunSource 1Source 2Source 4. This bizarre setup, combined with retrograde rotation, means the Sun rises in the westSource 1Source 2. Recent studies reveal its rotation rate even fluctuates due to its thick atmosphereSource 3Source 5Source 6.

ℹ️Quick Facts

  • **Venus sidereal day: 243 Earth days**Source 1Source 2Source 3
  • **Venus year: 224.7 Earth days**Source 2Source 4
  • **Solar day: 116.75 Earth days**—Sun rises west, sets eastSource 1Source 2
  • **Rotation changing**: Varies by minutes over yearsSource 3Source 5

💡Key Takeaways

  • Venus's **slow retrograde spin** makes its day exceed its year by 18 Earth daysSource 1Source 4.
  • Thick atmosphere likely **slows rotation**, preventing tidal lockingSource 6.
  • **Solar day shorter** than sidereal due to orbit-rotation interplaySource 1Source 2.
  • Recent radar data refines day length to **243.0226 Earth days**Source 5.
  • Uniform heat: No big day-night temp swingsSource 2.
1

Venus rotates once every **243 Earth days** (sidereal day), longer than its **224.7-day orbital year**Source 1Source 2Source 4. This means a full spin outpaces circling the SunSource 7.

Unlike Earth, Venus spins **retrograde**—clockwise—opposite its orbit. Sun rises in the west, sets eastSource 1Source 2. Slow pace stems from ancient impacts or atmospheric dragSource 1Source 6.

Solar day, noon-to-noon, is shorter at **116.75 Earth days** due to orbital motionSource 1Source 2. Over a year, Sun circles sky twiceSource 2.

2

Venus's **dense atmosphere**, 90x Earth's pressure, drags rotation via wind-momentum transferSource 1Source 3Source 6. Study suggests without it, Venus might tidally lock like the Moon—one side eternal daySource 6.

Univ. of California research ties stormy winds to slowdownSource 6. Thick clouds obscure surface, challenging measurementsSource 3.

Gravitational pulls from Sun/Earth may tweak spin slightlySource 3. No major eccentricity; orbit near-perfect circle at 0.72 AUSource 2.

3

NASA's Magellan clocked **243 days 26.6 min**; newer 29-year radar data: **243 days 30.5 min**Source 3. UCLA radar pins **243.0226 days**, varying by 20+ minSource 5.

Rotation isn't fixed—weather, tides alter it dailySource 3Source 5. Venus tilts **2.64°**, precesses every 29,000 yearsSource 5.

Ongoing missions like future VERITAS will refine thisSource 3. Venus Express confirmed shifts, cutting uncertaintySource 3.

4

Days/nights last ~58 Earth days each, but thick air blurs transitionsSource 4. Mean temp **462°C (863°F)** everywhere—no cool nightsSource 2.

Slow spin means minimal temp variation pole-to-equator or day-nightSource 2. Runaway greenhouse makes it hottest planetSource 2.

Imagine: Sun hangs midday for months, then weeks-long twilightSource 1Source 4. No vacations here!

5

Reasons for retrograde spin debated: ancient collision or atmospheric evolutionSource 1. Future probes target thisSource 3.

**Day > year** captivates; inspires Earth climate studiesSource 6. Venus, cloudy twin, warns of greenhouse extremes.

Track via radar as tech improves—Venus day still shiftingSource 5.

⚠️Things to Note

  • Measurements evolve; Magellan era vs. 30-year averages differ by minutesSource 3.
  • **Retrograde rotation** unique among planetsSource 1Source 2.
  • Atmosphere transfers angular momentum, tweaking spinSource 1Source 6.
  • Venus orbit most circular in Solar SystemSource 2.
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