Some Facts:

• 67 million miles / 108 million km from Sun
• orbits Sun in 225 days
• rotates on axis in 243 days (its "day" is longer than its "year")
• 7,600 miles in diameter - almost same as Earth (7,900 mi)
  
• Venus rotates retrograde (clockwise as seen from above north pole) - unlike most planets. (If we could view from its surface - and through its clouds - the sun would rise in the west and set in the east.)
• Venus is our nearest neighbor, coming within 24 million miles of Earth.
• Venus is very hot (>1,000 deg. F). It is thought to show a "runaway greenhouse effect."
• Atmosphere: primarily carbon dioxide; very dense (pressure 90 times that of Earth's air at sea level)
  Venus is entirely swathed in clouds rich in sulphuric acid.
• Surface: a large plain covers 60% of the surface. Two highland areas include high mountains (5 miles high), craters and active volcanoes.
  
• Exploratory missions:
  Venera 1 (Soviet) - launched in 1961, contact lost
  Mariner 2 - flyby on 12/14/62
  Many more...
• Several early astronomers reported seeing a moon of Venus - they were presumably seeing "ghosts" due to imperfections in the telescope optics.

Observing Notes

• Evening planet in Taurus in April & May 2004, then moves into daytime sky.
• Venus is at most 47 degrees from the Sun; it often has to be viewed in twilight conditions, though in spring 2004 it is high enough to be in dark sky.
• Extremely bright due to reflective cloud layer; use a moon filter or colored filter to see the phase shape.
• Phases:
  Venus is brightest in crescent phase, when it is closest to us, least bright when gibbous, farther away.
  We do not see "full Venus" - when it would be full, it is on the other side of the sun and hence invisible in the daytime sky.
  It was Galileo's observations of Venus' phases that convinced him that the planets revolve around the Sun, rather than around the Earth. If Venus revolved around Earth, we should see a full range of phases as we do with the Moon.
• Transits: Transits are rare, occurring in pairs 8 years apart, with about a century between pairs.
  There will be a tranist (not visible at our latitude) June 8, 2004 and again June 5, 2012. Should be visible from Europe. The last previous transits were in 1874 and 1882.
  In transit, Venus appears as a black disk on the surface of the sun. It is large enough to be seen naked-eye.
  

Filters:
(from the information provided with Celestron filter packages)

• Yellow (#8, 83% T): reveals low-contrast surface features
• Deep Yellow (#12, 74% T): reveals low-contrast surface features
• Deep Yellow (#15, 67% T): reveals low-contrast surface features
• Orange (#21, 46% T): during daylight observing reduces the brightness of the blue sky
• Light Red (#23a, 25% T): for daylight observing it reduces the brightness of the blue sky. Occasionally deformations of the terminator are visible.
• Red (#25, 14% T): for daylight observing it reduces the brightness of the blue sky. Occasionally deformations of the terminator are visible.
• Blue (#38a, 17% T): improves observing of dusky markings
• Violet (#47, 3% T): useful for increased contraxt of dark shading in upper Venusian clouds
• Green (#58, 24% T): Useful for Venusian cloud pattern studies
• Light Blue (#80a, 30% T): useful for increased contraxt of dark shading in upper Venusian clouds

Sources:
     Moore, Patrick. The Observer's Year. Springer, 1998.
     Harrington, Philip. Touring the Universe Through Binoculars. Wiley, 1990.