• Origin of name: Venus is the bright "Morning Star" or "Evening Star", and was sometimes given two different names [like Phosphoros and Hesperus]; Associated with the goddess of love and beauty, Venus (Romans), Aphrodite (Greeks), Ishtar (Babylonians).

  Overview: Earth's Sister Planet

  • View from Earth: [So bright it sometimes casts shadows!] Even with a telescope it looks smooth and featureless, from total cloud cover; It shows no moons* or rings.
  • Rotation and revolution: The rotation (first measured by bouncing radio waves off the surface) is slow and retrograde [with 243-day period], probably due to a past collision or friction between the atmosphere and the planet; The orbit is almost circular at 0.72 AU [225-day period].
  • Days and years: Because of the slow retrograde rotation, the solar day on Venus is much shorter than the sidereal one [116.8 Earth days long, compared to 243], and the Venus year is a little less than 2 Venus days!


  • Early missions: 1962-1974, NASA's Mariner series flybys; 1970s and 1980s, The Soviet Venera series landers (the first landing by spacecraft from Earth on another planet), which sent us the first photographs of the surface; Pioneer Venus (Probe 1978, Orbiter 1978-1982).
  • More recent: 1989-1994, Magellan orbiter; No active spacecraft near the planet since then, but the ESA launched the Venus Express mission in November 2005, and it is now in orbit around Venus; The ESA and Japan are planning missions.
  • View from orbit: UV satellite images show cloud patterns and winds; To map the surface features we must use radio waves.


  • Size: The radius is 95% of Earth's, and the density similar to Earth's [mass 80%] (How do we know what the mass is?).
  • Core: It is believed that Venus has a liquid metal core similar to the Earth's, and we have no seismic data to confirm this, but no magnetic field has been found (possibly because of the planet's slow rotation).
  • Activity: There is some evidence for plate tectonics and volcanism, but not on the same scale as on Earth; The absence of old craters may indicate that the planet behaves like a pressure cooker which occasionally explodes on a global scale, rather than gradually releasing heat; The high temperature may make the crust hotter and lighter than Earth's.

Exterior and Surface

  • Atmosphere: Thick, high pressure (90 atm near the surface, and a density 50 times greater than on Earth! Why?), made of CO2, N, with sulfuric acid clouds; Protects the surface against solar wind; Produces a strong greenhouse effect, but little erosion, because there is not much rain or surface wind.
  • Surface: It is 450°C (850°F) hot everywhere, always (including nighttime), because the atmosphere traps heat very effectively; Dry, of dusty rocks, with no water (it is too hot, but it may have had water in the past); Illuminated as much as the Earth's on an overcast day by orange light, because the atmosphere reflects mostly blue light.
  • Features: Radio maps show mountains, rolling plains, riverbeds, coronas, and some craters (from volcanoes and impacts, but no old ones or small ones, in part because small meteoroids break up in the atmosphere); But the surface is less rugged than Earth's, young and all the same age; We think that Venus was totally resurfaced 600-700 million years ago; There are cracks produced by temperature changes.

page by luca bombelli <bombelli at>, modified 7 oct 2013

Curiosities: Neith, the mysterious goddess of Sais, whose veil no mortal raised

In 1672, Giovanni Domenico Cassini, one of the prominent astronomers of the time, noticed a small companion close to Venus. Later, the object was seen by other astronomers as well. Most observations of the satellite were really stars seen in the vicinity of Venus.

Aug 13, 1892: E. E. Barnard recorded a 7th magnitude object near Venus. There is no star in the position recorded by Barnard, and Barnard's eyesight was notoriously excellent. We still don't know what he saw. Was it an asteroid that hadn't been charted? Or was it a short-lived nova that nobody else happened to see?