Astronomy Practice Exam

Why are Venus and Earth referred to as "Twins"?

1. They have the same atmospheric composition

2. They are similar in size and distance

3. They both have rings

4. They orbit the Sun at the same speed

The correct answer is: They are similar in size and distance

Venus and Earth are often referred to as "Twins" primarily due to their similarities in size and distance from the Sun. Both planets are relatively close to one another in terms of their physical dimensions; Venus has a diameter of about 12,104 kilometers, while Earth's diameter is approximately 12,742 kilometers. This similarity makes their sizes comparable in the context of the solar system. In addition to their size, both Venus and Earth orbit the Sun at relatively similar distances, with Earth being about 93 million miles (150 million kilometers) away, while Venus is approximately 67 million miles (109 million kilometers) from the Sun. This proximity contributes to their classification as terrestrial planets and underlines their shared characteristics, such as a solid surface and the presence of volcanic activity. Options that suggest similarities in atmospheric composition or the presence of rings do not accurately represent the relationship between the two. While they share some components in their atmospheres, Venus's atmosphere is thick and dominated by carbon dioxide, making it vastly different from Earth's nitrogen-oxygen-rich atmosphere. Additionally, neither Venus nor Earth has rings, which eliminates that option. The orbital speeds of Venus and Earth also differ, as Venus takes longer to complete an orbit around the Sun compared to Earth.