Astronomy Practice Exam

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Which planet is known for having a very slow rotation period?

Earth
Jupiter
Venus
Mars

The correct answer is: Venus

Venus is known for its very slow rotation period, which is approximately 243 Earth days. This slow rotation means that a day on Venus (the time it takes for Venus to complete one rotation on its axis) is longer than its year, which is about 225 Earth days—the time it takes to orbit the Sun. This unique characteristic of Venus results in unusual day-night cycles and contributes to its extreme surface temperatures due to the greenhouse effect. In contrast, other planets have much shorter rotation periods. Earth, for example, completes a rotation in about 24 hours, while Jupiter, the largest planet, has a very rapid rotation period of roughly 10 hours. Mars also has a rotation period close to that of Earth, taking about 24.6 hours, which supports the claim that Venus stands out amongst these options for its notably slow rotation.