Suppose that Venus had no atmosphere at all. How would the albedo of Venus then compare with that of Mercury or the Moon? Explain your answer.

Albedo is a key concept in understanding the reflectivity of celestial bodies like planets and moons. It signifies the measure of how much sunlight is reflected by a surface compared to how much light hits it. Put simply, it's the ratio of reflected radiation from the surface to incident radiation upon it. Albedo values range from 0 to 1, or from 0% to 100%, with 0 meaning no reflected light and 1 indicating total reflection.

A higher albedo value means that the body is more reflective, which can affect both its appearance from space and its thermal properties; reflective surfaces tend to stay cooler. This concept is critical in assessing the climate of planets and their potential to support certain conditions, like the presence of liquid water or ice. For instance, Earth's average albedo contributes to its ability to maintain temperatures conducive to life.

Venus' atmosphere is incredibly thick and is primarily composed of carbon dioxide, with clouds of sulfuric acid. This dense atmosphere reflects a large amount of sunlight, giving Venus one of the highest albedo measurements in the Solar System, at approximately 0.75. This also makes Venus the brightest planet in our sky. The high reflectivity is mainly due to the thick cloud cover, which scatters incoming solar radiation.

The Venusian atmosphere also has a runaway greenhouse effect, where the heat from the Sun is trapped, causing surface temperatures to soar to levels capable of melting lead. If Venus didn't have its atmosphere, it wouldn't reflect as much light. Instead, its surface made of basalt, a dark volcanic rock, would absorb more sunlight, making its albedo closer to that of Mercury or the Moon.

The reflectivity of celestial bodies, or how much light they reflect, is critical when studying their characteristics and behaviors. Bodies like Mercury and the Moon have lower albedos due to their rough, dark surfaces covered with regolith, a layer of loose material. This material doesn't reflect much sunlight, leading to albedos of approximately 0.12 for Mercury and 0.07 for the Moon.

Planets with atmospheres can have their reflectivity dramatically increased due to the scattering and reflection caused by atmospheric particles or clouds. In contrast, those without substantial atmospheres, like Mercury and the Moon, display reflectivity that directly correlates to their surface's inherent properties. Understanding the reflectivity of these bodies provides insights into their surface composition and atmosphere, if any, which in turn can help in studying topics such as climate, potential for life, and their evolution over time.