|
Venus is one of the planets in the solar system. It is the second in distance from the sun. Excluding the sun and the moon, Venus is the brightest thing in the sky. The planet is called the morning star when it appears in the east at sunrise and the evening star when it is in the west at sunset. Because of the lengths of the orbits of Venus and Earth from the sun, Venus is never seeable more than three hours before sunrise or three hours after sunset. When noticed through a telescope, the planet displays phases like the
moon. The phases and positions of Venus in the sky repeat with the syndic period of 1.6 years. Transits that cross the face of the sun are rare, occurring
in pairs at pause a little more than a century. The next two will be in 2004 and
2012. Venus's complete cloud cover and deep atmosphere make it difficult to
study from earth, and most knowledge of the planet has been obtained through the
use of space vehicles, particularly those carrying probes that descend through
the atmosphere. The first flyby was that of Mariner 2, launched by the United
States in 1962, followed by Mariner 5 in 1967 and Mariner 10 in 1974. The surface temperature on Venus is highly uniform and is about 462° C
(864°F). The surface pressure is 96 bars. The atmosphere of the planet contains
nearly all carbon dioxide. The cloud base is at 50 km (31 mi.), and the cloud
dust is mostly concentrated sulfuric acid. 97 percent of Venus's atmosphere is
carbon dioxide. About 3 percent of the Venusian atmosphere is nitrogen gas. By
comparison, 78 percent of earth's atmosphere is nitrogen. The hydrogen atoms of
the water electrons could have been lost to space and the oxygen molecules lost
to the crust. Another possibility is that Venus had hardly any water to start.
Venus rotates very slowly on its axis, opposite to the direction the Earth does. The powerful radar aboard the Magellan spacecraft unveiled huge active volcanoes. The biggest volcano has a base of more than 700 km (435 mi.) wide.0 |
|
|
