Venus is the second planet from the Sun and is our nearest neighbour, both in terms of distance and size. It's surface is completely obscured by dense white clouds, with a hint of yellow caused by sulphur. The high reflectivity of the clouds makes Venus a brilliant object in the west after sunset or in the east before dawn. At its brightest it can even be seen in broad daylight.
Because the orbit of Venus is inside that of the Earth it shows phases like that of the Moon. When it is on the far side of the Sun we see all of the sunlit side so it appears full, although small. As it comes towards the Earth on its orbit it appears progressively larger but presents more of its dark side towards us. Therefore, when it appears furthest east or west of the Sun we see it with a 50% phase (i.e. half-moon), and when it is at its brightest the phase is about 35% (a thick crescent). When it is nearest to the Earth (inferior conjunction) it is between the Earth and Sun so presents its dark side entirely towards us. Although the it cannot normally be seen at this time, it is possible to see it as an extremely slender crescent a few days before and after this event.
On rare occasions Venus really does line up exactly between the Earth and the Sun, and on such occasions Venus is silhouetted as a black circle against the glare of the Sun. The outline of Venus is large enough to be seen with the naked eye when this happens, but precautions must be taken to prevent blinding yourself looking at the Sun, just as for a partial eclipse. The last transit took place on 8 Jun 2004.
Binoculars reveal the phase quite easily, especially when it is less than 50%. However, even a telescope will show little in the way of features except for occasional vague markings and irregularities in the phase caused by storms in the dense atmosphere. Venus has no moons.
|Distance from Sun (Million km):||107 (min)||109 (max)|
|Min. Distance from Earth (Million km):||29|
|Orbital Period:||225 days|
|Mean Interval between Inferior Conjunctions:||584 days|
|Rotation Period:||243 days|
|Apparent Diameter (arc seconds):||65 (max), 10 (min)|
|Max. Apparent Brightness (magnitude):||-4.6|
Transit of Venus, 8 Jun 2004
|Jet Propulsion Laboratory Venus pages|