Rotation and Revolution



Rotation and Revolution

A planet is a large body that shines by reflected light and travels in a stable path around a star. The sun is the star of our solar system and controls the motion of all the planets that travel around it. The planets are illuminated, or lit up, by sunlight. Some planets may be mistaken as bright stars on a clear night. However, when carefully observed, planets shine with a steady glow of reflected light, whereas, stars appear to flicker or twinkle.

A planet has two important motions that occur at the same time:

1. It spins on an axis.

2. It moves in an orbit around a star.

Rotation is the spinning of a planet on its axis. The time it takes a planet to complete one spin is called its period of rotation. The period of rotation is known as a day on that planet. The time it takes for a planet to complete one rotation varies from planet to planet.

As the planet rotates on its axis, half of the planet is bathed in sunlight and half is not. The side of the planet facing the sun experiences daytime; the other half has nighttime. On Earth, a period of rotation lasts about 24 hours or one day.

Revolution is the movement of a planet in a path, called an orbit, around a star. The period of revolution is known as a year on that planet. The time it takes for a planet to complete one revolution depends on the distance between the planet and the star. On Earth, a period of revolution lasts 365 days or one year.

Rotation and Revolution

Planet or Object |Average Distance from sun (millions of km) |Average orbital speed

(km/s) | |Period of Revolution

(Earth years) |Period of Revolution

(Earth days)

[Earth year x 365] | |Period of Rotation

(Earth days) |Period of Rotation (Earth hours)

[Earth days x 24] | |Mercury |58 |47.8 | |0.24 |87.6 | |59 days |1416 | |Venus |108 |35 | |0.62 |226.3 | |243 days |5832 | |Earth |150 |29.8 | |1 |365 | |1 day |24 | |Mars |228 |24.2 | |1.9 |693.5 | |1.03 days |24.72 | |Jupiter |778 |13.1 | |12 |4380 | |0.41 days |9.84 | |Saturn |1427 |9.7 | |29 |10585 | |0.43 days |10.32 | |Uranus |2871 |6.8 | |84 |30660 | |0.72 days |17.28 | |Neptune |4497 |5.4 | |165 |60225 | |0.67 days |16.08 | |

1. Calculate the “Period of Revolution (Earth Days)” for each object by multiplying the “Period of Revolution (Earth Years)” by 365.

2. Calculate the “Period of Rotation (Earth Hours)” for each object by multiplying the “Period of Rotation (Earth Days)” by 24.

Turn over your paper and complete the questions on the back.

Jupiter 19. Which planet spins the fastest on its axis, or has the shortest period of rotation?

Neptune 20. Which object has the longest year, or longest period of revolution?

Mercury 21. Which object has the shortest orbit, or shortest period of revolution?

Venus 22. Which object has the longest day, or longest period of rotation?

23. How are the “Average Distances From the Sun” and the “Period of Revolution” related?

The further a planet is from the sun, the longer its period of revolution

More 24. Planets closer to the sun than Earth take a shorter amount of time to revolve around the sun. Therefore, their years are shorter. Do you have more or fewer birthdays on planets that are closer to the sun than Earth?

Fewer 25. Planets farther from the sun than Earth take a longer time to revolve around the sun. Therefore, their years last longer. Do you have more or fewer birthdays on planets that are farther from the sun than Earth?

Between 44 – 48 26. A year on Mercury is .25 of a year on Earth or ¼ of Earth’s year. It revolves around the sun 4 times in one Earth year. How old would you be on Mercury? (Careful! Check your answer to #24 before you write down your answer here.)

Between 5 – 7 27. A year on Mars is almost twice as long as a year on Earth. Or, Earth takes half the time Mars does to revolve around the sun. About how old would you be in Mars years? (Careful! Check your answer to #25 before you write down your answer here.)

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