Venus can be the brightest object in the sky, beside the sun
and moon. Since its orbit is inside that of the earth, we see
Venus only when we are looking in the general direction of the
This bright planet is
visible only during the first few hours after sunset, when it
is known as "the evening star," or before sunrise, when
it is known as "the morning star." Venus can be brighter
than magnitude -4, and can even cast shadows.
Venus is covered with thick layers of clouds through which we cannot see. From earth, we see no structure, though we do see Venus go through phases as it orbits the sun. (Only planets that have orbits smaller than the earth's - Venus and Mercury - can go through a crescent phase. The fact that Venus goes through a complete cycle of phases, including the crescent phase, was discovered by Galileo and was a major proof of the validity of Copernicus' idea that the sun rather than the earth is at the center of the solar system.)
When Venus is just about to pass between the sun and us, it appears as a crescent and is at its largest. We may even see sunlight bent around toward us through its thick atmosphere. When Venus appears at the same longitude along the ecliptic as the sun, it is at conjunction. When Venus lies nearly on a line of sight between the sun, and us it is at inferior conjunction. When we can see all of Venus' lighted side (its "full" phase), the planet is on the far side of the sun, at its farthest point from us and therefore at its smallest. It is then at superior conjunction.
From spacecraft looking through ultraviolet filters from the vicinity of Venus, we have been able to study the circulation of the planet's clouds. The Pioneer Venus Orbiter in 1979 even compiled a map of Venus' surface, using radar.
A series of Soviet spacecraft have landed on Venus and sent
back photographs of its surface (Another link.) From studies of
the composition of the surface, we know that the same kind of
geological processes that formed the earth's surface also were
at work on Venus. The earth, though, has several continents and
is mostly covered with deep ocean basins. Venus, on the other
hand, has only a few small continents and few deep basins; it
is mostly covered with broad rolling plains.