Venus

Provenance-Backed Scientific Measurements

Every measurement below preserves its unit, uncertainty interval, observational method, reference epoch, quality status, and primary catalog source. See Uncertainty & Provenance for how competing measurements are handled.

J2000 Equatorial Sky Chart & Culmination Altitude

The chart below plots Venus — Orbital, Atmospheric & Phase Data at RA 21h 10m 00.00s, Dec -18° 00′ 00.0″ within Capricornus, alongside peak meridian transit altitudes for 40°N and 30°S observers. Use the RA/Dec Coordinate Converter to compute exact culmination altitude for your latitude.

Astrophysical Context & Structure

Measuring 95 percent of Earth's diameter (12,103.6 kilometers) and 81.5 percent of its mass, Venus formed in the same inner Solar System neighborhood as Earth yet evolved into a starkly different world. It travels along the most circular orbit of any planet (eccentricity 0.0068) at 0.7233 astronomical units in 224.70 days. Curiously, Venus rotates backward (retrograde, obliquity 177.36 degrees) once every 243.025 Earth days—the slowest spin of any major planet—while its upper cloud deck super-rotates around the globe in just four days.

Beneath a global, highly reflective (Bond albedo ~0.76) cloud deck of concentrated sulfuric acid droplets between 48 and 70 kilometers altitude lies a crushing 96.5-percent carbon dioxide atmosphere with a surface pressure of 92 bars. This extreme greenhouse blanket bakes the basaltic surface to an isothermal 737 K (464 °C)—hotter than sun-baked Mercury and hot enough to melt lead. Synthetic-aperture radar mapping from the Magellan orbiter revealed volcanic plains, pancake domes, coronae, and highlands (Ishtar and Aphrodite Terra) with fewer than a thousand impact craters, indicating major volcanic resurfacing within the past 300 to 700 million years.

When Galileo Galilei turned his telescope on Venus in autumn 1610, he watched it swell from a small gibbous disk to a giant thin crescent over several months—providing decisive observational falsification of the Ptolemaic geocentric model. At greatest elongation (45° to 47° from the Sun), Venus shines near magnitude -4.5, rising to -4.9 during its crescent phase when it approaches within 40 million kilometers of Earth.

Practical Visual Observing Guide

• Outshines every celestial body except the Sun and Moon (reaching V = -4.9); easily visible in broad daylight to the naked eye when one knows exactly where to look.
• Swings from a 9.7″ full disk at superior conjunction to a huge 66.0″ thin crescent at inferior conjunction—resolvable as a crescent even in 7x50 binoculars.
• Ultraviolet (320–390 nm) and violet (#47 Wratten) filters allow amateur astrophotographers to record the dark Y-shaped cloud markings rotating across its upper atmosphere.

Catalog Cross-Identifications & Aliases

Common Aliases: Phosphorus · Hesperus · Morning Star · Evening Star

Related Objects, Comparisons & Guides

Scientific Sources & Dataset Provenance

• NASA/JPL Solar System Dynamics & Planetary Fact Sheets (DE441 (2021/2026)): Park, R. S., et al. 2021, AJ, 161, 105 (The JPL Planetary and Lunar Ephemerides DE440 and DE441) — NASA Jet Propulsion Laboratory / GSFC