Sponge - Name two surface features of Mercury that are not found on the Moon.

Venus is often called the “morning star” or “evening star”.It was thought to be two separate objects by early astronomers. It was known to be one planet by the 6th century B. C.

Semi-major axis A. U. Eccentricity is closest to a perfect circle of all the planets. Orbital period is 225 days (7.5 months).

Venus is the third brightest object in the sky (after the Sun and the Moon).

Venus is ten times brighter than Sirius, the brightest star. Venus is so bright that it is visible in the daytime if one knows where to look.

Venus is highly reflective with an albedo over 0.7.

It is not brightest when in the full phase because at this time it is furthest from Earth. Superior conjunction - Venus and Earth on opposite sides of the Sun.

It is actually brightest just before and just after inferior conjunction because Venus is so close to Earth. Inferior conjunction - Venus and Earth on the same side of the Sun. Venus is “new”.

Venus is brightest when it is at these two points in its orbit.

Venus orbits “counter- clockwise” as viewed from above the north celestial sphere (as do all the other planets).

Venus does transit the Sun as viewed from Earth, but transits are more rare than transits by Mercury, since Venus is farther from the Sun.

Transits occur in pairs eight years apart, less than once per century. The next ones are due in 2117 and 2125.

Radius km 0.95 Earth’s Mass x g 0.82 Earth’s Density g/cm 3 very similar to Earth

Mercury Venus Earth Mars

The rotation rate was not found until the 1960’s using radar. (The surface of Venus cannot be viewed because of the thick cloud cover.)

Venus rotates on its axis once every 243 days!! (This is longer than the 225 day year.) In addition, the rotation is retrograde! (clockwise as viewed from above the north pole)

One of the greatest questions in astronomy is why Venus’ rotation is retrograde and so slow.

Venus is completely covered by clouds. The upper level clouds rotate the planet in 4 days, much faster than the planet’s surface. The upper level winds reach speeds of 400 km/hr.

The atmosphere contains LARGE amounts of CO 2 (actually there is little else).

Measurements in the 1950s indicated that the surface temperature is near 600K. More recent measurements indicate that the temperature is actually closer to 750K!! This is the hottest surface temperature of any planet or moon in the solar system.