Being one of the brightest objects in space(besides earth and the moon) visible from earth, Venus was seen by ancient astronomers. As they mapped the many stars of the sky, they noted that Venus was visible at certain times during nights and in the morning. It soon became known as the evening star when it is in the west at sunset, and the morning star when it appears in the east at sunrise. Venus is never visible more more than three hours before sunrise and three hours after sunset. At these times Venus became known as Hesperus at night and as Lucifer during morning. Soon after they named it Venus, after the goddess of love and beauty. A Roman goddess originally of gardens and fertility who became identified with the Greek Aphrodite as `goddess of love.
Venus has also been refered to as Earth's "twin". Although size is very similar, Venus is very different in comparison to the Earth. The following table compares both of the planets. Take a Look!
Venus | Earth |
|
| miles from sun | 67 miles | 93 miles |
| rotation period | 225d/7 1/2 months | 365d/12 months |
| tilt | 178 degrees | 23.45 degrees |
| direction of rotation | retrograde motion | forward motion |
| diameter | 7,515 mi | 7,926 mi |
| surface temperature | 470 degrees Celcius | 22 degrees Celcius |
| number of moons | 0 | 1 |
Venus is known to be one of the few terrestrial planets,or inner planets. Along with Mercury, Earth, and Mars, Venus is one of the closest planets to the sun and is separated from the outer planets by an asteroid belt. Infact, it is the second farthest planet from the sun. Many of Venus's features are similar to that of Earth's such as mountains, valleys, canyons, craters, and volcanoes. Earth-based radio telescopes allow us to map out only some of the surface when the two planets are the closest.
Solviet probe data combined with that of the Pioneer Venus 1 a fairly good global survey was possible. The survey showed that the surface was mostly a rolling plain and two continent- sized highlands. Named Ishtar Terra high and Ishtar Terra, they extend halfway across the equatorial region. Better yet, huge active volcanoes, large lava flows, and various meteorite craters were detected by a radar of more power aboard the Magellan spacecraft. One of these craters is known to be almost 160 km (100 mi) across. Also, probes and surveys have evidence that tectonic activity has taken place on Venus. Ridges, canyons, and a troughlike depression are just that evidence. Natural radioactivity of rocks has also been measured which suggests that volcanic activity occured due to the differeniated, or chemically seperated, material on the planet.
Geologists have had trouble learning about Venus's surface due to its atmosphere. The atmosphere consists of 98% of Carbon Dioxide and about 2% Nitrogen Gas, in comparison to Earth's 78% Nitrogen. The surface temperature on Venus is very high reaching about 470 degrees Celsius. Infact, astronomers believe that the surface temperatures of Venus create sort of a greenhouse affect. This process is done by trapping the sun's energy and preventing heat from escaping.
A thick cloud measuring about 50 km(31 mi)surrounds the planet. This cloud is made up of Sulfuric Acid particles. Sulfuric acid and water have several chemical reactions. Water is exteremely rare on Venus, therefore we can understand why life, as we know it on earth, is unsustainable. On Earth, sulfuric acid is carried down by rain(acid rain) and reacts with surface materials, where as on Venus acid evaporates and a cloud base is left remaining in the atmosphere. These clouds can be detected by ultraviolent wavelengths because of the pale yellow impurity within the cloud. The sulfur dioxide may be indicated when volcanic eruptions belch clouds of sulfur dioxide into the skies.
Information about wind motion can be determined by certain cloud patterns. upper-level winds cover the planet completely and circle the planet at 225 mph, blowing at every latitude from pole to equator. The high-speed winds are probably a result of Venus's momentum from a transfer of it's slow movement. From the surface up to 10 km(6 mi) altitude, wind speeds are only about 3 to 18 km(2 to 11 mph). Despite the many surface winds of the planet, Venus's tremendously dense atmosphere is almost stagnant, or lacking movement.
The deep atmosphere and the complete cloud cover make Venus difficult to study from Earth. Therefore, most of the knowledge accumulated has been from orbiting space probes and vechicles by descending through the atmosphere. In 1961 the Solviet launched space probes from Veneras 4 to 8 into the atmosphere. However, they had difficulties due to the intense pressure of the planet's atmosphere(90 times that of Earth's)as they attempted to land. Veneras 7 and 8 reached surface in 1970 and 1972. Continued series of probes followed; 9 and 10 in 1975, 11 and 12 in 1978, 13 and 14 in 1981, and 15 and 16 in 1983. These probes managed to obtain photographs back to earth. In 1962 the Mariner2 was the first flyby mission launched by the United States. Also, followed by Mariner5 in 1967 and Mariner10 in 1974. Later, the United States sent two Pioneer Venus missions in 1978. Four probes were sent to the surface while the craft remainingexplored the upper atmosphere in the Pioneer Venus2 mission. An orbiter, Pioneer Venus1, continues to measure the upper atnmosphere. In 1990 images were transmitted through radar after the Magellan probe launched towards Venus in 1989.
Venus exhibits phases like the earth's moon. Venus appears smallest in full because it is when it is on the far side of the sun from the earth. During crescent phase is when its (-4.4 magnitude) at its brightest. The synodic period of 1.6 years is repeated of the phases and positions of Venus in the sky. Passage across the face of the sun are rare, however occur in pairs at intervals of a little more than a century. The next two will take place in the years 2004 and 2012.
