Physical Science:

Venus [Figure 12.1.3] is the second planet from the Sun and is sometimes called Earth’s sister planet due to its similar size and composition. However, Venus has a very different climate and geology than Earth. Venus has a thick atmosphere primarily composed of carbon dioxide, with clouds of sulfuric acid that completely obscure its surface. The atmospheric pressure on the surface of Venus is about 90 times greater than Earth’s, making it a very hostile environment for exploration. Despite the challenges of studying its surface, scientists have been able to use radar and other methods to create maps and images of Venus. These have revealed that Venus has a diverse landscape, with highland regions, flat plains, and thousands of volcanic structures. One of the most striking features on Venus is the massive shield volcano known as Maat Mons, which is one of the highest mountains in the solar system. Venus also has a number of other large volcanic structures, including the volcano Ozza Mons and the pancake-shaped volcano Theia Mons. Another notable feature on Venus is its extensive system of canyons and valleys, which are similar in appearance to those found on Mars. These features provide evidence of past tectonic activity and suggest that Venus may have experienced significant geological changes over time.

Venus rotates very slowly, taking about 243 Earth days to complete one rotation, which is longer than it takes for Venus to complete one orbit around the Sun (which takes about 225 Earth days). As a result, Venus has a very unusual day and night cycle. On Venus, a single day (one complete rotation) lasts longer than a year (one orbit around the Sun). This means that a day on Venus lasts about 117 Earth days, while a night on Venus also lasts about 117 Earth days. However, it’s important to note that the atmosphere of Venus is very thick and opaque, which makes it difficult to define day and night in the same way we do on Earth. Instead, Venus experiences a kind of "twilight" all the time, with the level of light varying depending on the location and altitude in the atmosphere.

Like the Moon, Venus exhibits phases as seen from Earth. The phases of Venus occur because Venus orbits the Sun, and as it does so, its position relative to the Earth changes, causing us to see different amounts of its illuminated surface. When Venus is on the opposite side of the Sun from Earth, it is in its "full" phase, with its entire illuminated surface facing away from us. As Venus moves closer to Earth in its orbit, it begins to appear as a "waning gibbous" phase, where it is more than half illuminated but not yet fully illuminated. When Venus reaches its closest point to Earth in its orbit, it appears in its "half" or "first quarter" phase, with half of its illuminated surface facing us. As Venus moves further along in its orbit, it appears as a "waxing crescent" phase, with less than half of its illuminated surface visible. Finally, as Venus approaches its position on the opposite side of the Sun from Earth, it appears as a "new" phase, with its fully illuminated surface facing away from us. Venus then moves back around the other side of the Sun and begins the cycle of phases again. The phases of Venus are one of the key pieces of evidence that supported the heliocentric model of the solar system, where the planets orbit the Sun, rather than the geocentric model, where the Earth was thought to be the center of the universe. The phases of Venus were first observed by Galileo in 1610, and their regular pattern was later explained by the heliocentric model proposed by Copernicus.