The lack of change in the intensity and shape of Venus over the course of six months is due to a combination of factors related to the nature of Venus itself and its position relative to Earth.
Atmosphere: Venus has a thick atmosphere composed mainly of carbon dioxide, with clouds of sulfuric acid. These clouds create a highly reflective layer that reflects a significant amount of sunlight back into space. As a result, Venus appears bright in the sky, and its overall intensity remains relatively constant over time.
Slow rotation: Venus rotates very slowly, taking about 243 Earth days to complete a single rotation. This slow rotation means that there are minimal changes in the orientation and shape of Venus as observed from Earth over a period of six months. The visible features and markings on Venus, such as its cloud patterns, remain relatively stable during this time.
Similar distance: While Venus and Earth are both in orbit around the Sun, their orbits are not perfectly aligned. However, over a span of six months, the distance between Venus and Earth does not change significantly. As a result, the apparent size and shape of Venus as seen from Earth remain relatively constant.
Overall, the combination of Venus's thick atmosphere, slow rotation, and consistent distance from Earth contributes to the perceived lack of change in its intensity and shape over a period of six months.