It may seem obvious, but it’s the simple truth: planets rotate because there is no force to stop them. The fact is that everything tends to maintain its movement if nothing appears to oppose it. This story began with the Big Bang, the explosion that gave rise to the Universe 15 billion years ago. Since then, the particles of the cosmos have been constantly attracting and colliding with each other. It was precisely from these bumps that rotational movements were born. It is as if the Universe were an immense imaginary pool table in which there was no force capable of stopping the balls. Imagine the mess: one shot would be enough to start an eternal bump! In this confusion, the balls would inevitably rub against each other, giving rise to rotational movements. The Earth’s spin, for example, can be reconstructed from the time when the matter that today makes up everything that exists in the solar system was just a cloud of gas and dust lost in the middle of the galaxy. Accompanying the peak of the Milky Way, this cloud was already spinning.
But some 5 billion years ago, one of the most important rules in the Universe began to make a difference. We’re talking about the law that says anything that gets more compact ends up running faster. That’s what skaters do when spinning, shrinking the body to turn quickly. In the case of the cloud, the rotation caused it to begin to condense, and the more it compacted, the faster it spun. This circular reaction caused the particles in the center of the cloud to condense so violently that the temperature in the middle reached millions of degrees Celsius. It was enough to trigger the nuclear reactions that “ignited” the Sun. This frantic, rotating plate made more and more particles slam into each other.
Some gathered so much dust and rock that they grew to the point of becoming planets. “As the old disk rotated, the new planets retained this characteristic and began to rotate as well”, says astronomer Roberto Dias da Costa, from the University of São Paulo (USP). Each one of them, however, makes its turns at its own time and direction, as you can see in the infographic that illustrates these pages.
In the solar system, Venus and Uranus rotate unlike other stars
VENUS
Rotation time: 243 days
Translation time: 224 days
Almost all planets rotate counterclockwise, following the direction of the «disk» that gave rise to them. But Venus rotates in reverse. This likely happened because it was hit by a very large, planet-sized object during the infancy of the solar system. In addition to the odd rotation, the super blow left Venus with another trauma: over there, a day lasts longer than the year itself
URANUS
Rotation time: 17 hours
Translation time: 84 years
Like Venus, Uranus also rotates in the opposite direction to the other planets – according to astronomers, also because of some gigantic impact. But its trademark is another: Uranus is a planet “lying down”. Seen from Earth, it appears to be spinning on its side. This makes the “nights” in the dark half last 42 years, or the time it takes the planet to orbit around the Sun.
SUN
Rotation time: 25 days (at the equator)
Time of translation: 225 million years
A lot of people don’t know, but the Sun also rotates around its own axis. By the way, it is a very strange movement: as the surface is not solid, the rotation is no longer uniform. Thus, the equator completes a revolution three days before the poles. To complete, the star also revolves around the center of the Milky Way, but the end of the tour takes no less than 225 million years
EARTH
Rotation time: 23 hours and 56 minutes
Translation time: one year
Like all planets, Earth rotates faster where the circumference is greatest — just think of the planet as a disk: A point that is on the outermost band rotates faster than one closer to the center. Therefore, at the equator, the speed of rotation is 1674 km/h. In a city like São Paulo, located further south, the speed drops to 1,535 km/h. Rotation also causes a centrifugal force that cancels out some of gravity. This explains why the same person weighs 250 grams less in Maranhão, close to the equator, than in Norway, in the far north, where rotation is lower.
JUPITER
Rotation time: 9 hours and 55 minutes
Translation time: 11.9 years
The largest planet rotates the fastest, reaching an incredible 40,000 km/h at the equator. It is no coincidence: massive stars tend to retain a greater amount of movement from the “disk” that gave rise to the planets, as they were born from a thicker band of it. Saturn, which is almost the size of Jupiter, is also fast: it revolves around its axis in 10 and a half hours.
SKY FROM ANOTHER WORLD
Absurd rotation of pulsars forms a surreal landscape
When an object of gigantic mass contracts, its rotation increases dramatically. This is the case of pulsars, stars that were millions of kilometers in circumference but that diminish in size with the end of their “fuel”. A pulsar has a mass equivalent to that of the Sun, squeezed into a sphere about 20 kilometers in diameter. This unimaginable concentration of matter makes them rotate around their own axis about 30 times per second. From the surface of a pulsar, you would see the sky just like the montage above: the stars would fly by so fast they would look like static streaks.
SUPERSONIC EARTH
At that moment, we are almost 1 million km / h
The fact that we rotate with the Earth’s rotation at a speed slightly higher than the speed of sound (1 224 km/h) is already surprising. But we are much faster. The planet revolves around the Sun at no less than 107,000 km/h, taking us on a ride. And the Sun itself pulls us at over 800,000 km/h as it revolves around the center of the Milky Way. Adding it all up, we tear through the galaxy at almost 1 million km/h!