Most planets in our solar system—including our Earth—spins counter-clockwise, and it is considered the normal direction of rotation in our solar system.
In fact, one of the most remarkable feats of our Milky Way galaxy is that nearly all the revolutions and rotations of the objects in it are in the same direction.
The same phenomenon even can be seen in asteroids and the satellites of the planets like our Moon. The sun itself also rotates in the counterclockwise direction.
However, Venus and possibly Uranus are the anomalies in our solar system, as they rotate clockwise rather than counter-clockwise.
Venus’s revolution cycle is once every 225 Earth days, but it rotates clockwise with a period of 243 days.
Uranus, however, is rather unique that the planet is tilted almost 90° on its side, making its direction of rotation rather ambiguous, but many experts agree that Uranus also rotates clockwise.
Why Does Venus Rotate Clockwise?
Venus is often thought of as the twin brother (or sister) of our Earth. The second planet in our Solar System has a similar mass, size, density, and even chemical composition to our Earth.
However, Venus, unlike our earth, has a very hot temperature and extreme air pressure, so although they look similar to each other, they are also very different.
So, why does Venus rotate differently from our Earth and all the other planets except Uranus?
It is believed that in the distant past, Venus rotated in the same direction, but something came along that changed the rotational direction of Venus (and Uranus).
There are a few theories to explain why Venus rotates clockwise instead of counter-clockwise.
One of the most widely held beliefs is that due to Venus’s extremely dense atmosphere, the Sun also offers a very strong gravitational pull to the planet, causing strong atmospheric tides. Sometime between the formation of Venus and today, these strong tides caused the flip in Venus’s rotation.
In the past, however, it is widely accepted that Earth was actually the culprit. Earth goes twice around the Sun in 728.50 days, while at the same period Venus rotates three times on its axis (in 729.27 days), so Earth and Venus are locked in a 3:2 tidal resonance.
It was believed that this tidal resonance was what caused Venus’s odd rotation direction. However, nowadays experts agree that the force generated by the Earth doesn’t seem to be strong enough to flip Venus’s rotation.
Another theory is that in the early days of our Solar System, there were a lot more objects, planets, and mini-planets that orbited our Sun, and they clash with each other leaving only the planets and satellites we have today.
Our Moon, for example, was believed to be formed when a Marz-sized ‘planet’ collided with the Earth, and the Moon is the leftover material that has merged.
The theory is that the same collision also happened with Venus, but the phenomenon didn’t form a satellite, but rather stopped and reversed Venus’s rotation.
Indeed, another uniqueness of Venus is that the planet has no satellite/moon at all.
Alex Alemi and David Stevenson from Caltech proposed that there have been not one, but two of these impacts in Venus’s long history.
The first impact actually formed a moon, but another impact on the opposite side reversed its rotation and caused the moon to also collided with Venus, hence the Venus we have today.
So, nobody is 100% sure about what happened to Venus’s rotation, but we can almost be sure that Venus originally rotated counter-clockwise.
Here is an interesting video from NBC News that discusses the rotation of Venus:
Interesting Facts about Venus
Venus is further away from the Sun but is hotter than Mercury
Venus has a very high mean temperature of 462°C although it is further away from the Sun than Mercury. This is because of Venus’s high concentration of carbon dioxide in its atmosphere, creating a very intense greenhouse effect.
As we know, carbon dioxide traps heat in the atmosphere, causing the temperature of the planet to rise higher.
A day on Venus lasts more than 200 Earth-days
To be more exact, a day on Venus lasts around 243 Earth-days. A unique thing, however, is that a Venusian year only lasts about 224 Earth-days. So a day on Venus is longer than a year.
Venus has an extreme atmospheric pressure
Venus’s atmospheric pressure is almost 100 times stronger (to be more precise, 92 times) stronger than Earth’s pressure. To put this into context, the pressure is equivalent to being inside Earth’s ocean with around 600 miles of depth.
So, most relatively small asteroids would be crushed by this extreme atmospheric pressure. This is why we can’t find any small surface craters on the planet.
Venus as a very weak magnetic field
Due to its many similarities with Earth and its extreme atmospheric feature, many scientists originally expected Venus’s gravity field to be at least similar in strength to Earth’s.
However, a possible explanation is that Venus has no solid inner core due to its temperature, weakening its magnetic field.
Venus is our brightest planet
Venus is obviously not the largest planet in our Solar System but viewed from earth, it is the brightest of all the planets we can observe due to its proximity from Earth.
It is also the second-brightest object in the sky after the Moon. Venus is not only bright in the nighttime sky, but also in the morning.
Venus has Phases
Since Venus orbits the sun inside the Earth’s orbit, the planet appears to have phases, just like the moon.
Venus can be viewed in its full phase when it is on the opposite side of the sun and appears in a new phase when it is between the sun and the Earth.
Venus has atmospheric super-rotation
Venus’s atmosphere rotates faster than the planet itself, a phenomenon known as super-rotation. In fact, the atmosphere circles Venus in just 4 Earth days, while Venus’s actual rotation, as we know, is 243 Earth days.
Venus’s atmosphere might contain life
A rather interesting fact is that we can observe dark streaks in Venus’s atmosphere, and this is how Venus’s super-rotation was found. What these dark streaks are still unknown, but there’s a possibility that they are, in fact, microbial life.
While Venus’s surface is really hot with very high atmospheric pressure, between 31 and 37 miles above the planet’s surface, the temperature and pressure are similar to Earth’s surface. It is possible the microbes are coated in a material that can withstand the atmosphere’s sulfuric acid.
A unique thing about Venus’s orbit is that it is very circular. With an eccentricity of only .00678, in fact, Venus has the most circular orbit compared to all the other planets in our Solar System.
The difference between Venus’s aphelion (1.09 x 108 km) and its perihelion (1.07 x 108 km) is only 1.46 x 106 km, very small compared to other planets.
Venus was named after the Roman goddess of love and beauty, the counterpart to the Greek goddess Aphrodite. It is believed that the planet was given this name due to its bright, shining beauty in the morning sky.
Of the five planets known to ancient astronomers, Venus would have been the brightest and the most beautiful.
The same side of Venus always faces the Earth
When they are at their closest. It is believed that this phenomenon is made possible due to Earth’s gravitational influence over Venus.
You can learn more about Venus here.
Why Does Uranus Rotate Clockwise?
Unlike Venus of which we are pretty sure that it is indeed rotating clockwise, we can’t say the same about Uranus which has a rather unique rotation and planetary axis.
Most planets have planetary axes that are perpendicular to the orbital plane, but Uranus has a very tilted axis of 97.7º with its pole pointed toward the other planets’ equatorial planes.
This phenomenon not only causes the radical seasons and temperatures on Uranus but also cause unusual days at Uranus’s poles.
Uranus has the most extreme seasons in the solar system due to this unique tilt. For nearly a quarter of each year (Uranian year), the Sun shines directly over each pole, so the other half of the planet experiences a very long and dark winter for 21 Earth years.
With this condition, Uranus isn’t really rotating in the regular clockwise or counter-clockwise direction, but rather, it rotates vertically (although if we assume the planetary axis is perpendicular, it rotates clockwise).
Same with Venus, most experts agree that Uranus also originally rotates counterclockwise until a massive impact stopped and then shifted its rotation.
It is believed that Uranus, in its history, collided with an Earth-sized object which caused this rotation.
There are, however, some objections to this theory. For instance, Uranus has a system of 27 moons composed of equal parts of rock and ice. If the planet suffered a massive impact, the energy should be enough to vaporize the ice so Uranus shouldn’t have any ice moons left.
Also, Uranus and Netuno currently have similar rotation periods (a strong suggestion that they were formed together at the same time).
If Uranus had suffered an impact that altered its axis and rotation direction, this rotation period would also have been altered.
Gwenael Boue and Jacques Laskar from Paris Observatory, however, had another theory that involves no collision. Uranus, apparently, had a very large moon with around 0.1% of Uranus’s mass.
It is believed that the gravitational force interaction between Uranus and this moon changed Uranus’s planetary axis and its rotation to the way they are now. Also believed is that the moon was ejected from the system when Uranus encountered another huge planet.
There are other theories that suggest that a series of collisions caused the shift of Uranus’s tilt and rotation, rather than a single massive impact.
However, we can only speculate on what may have happened since whatever it is, it happened millions if not billions of years ago.
Interesting Facts About Uranus
Uranus makes one trip around the sound every 84 Earth years, due to its unique tilts, during some parts of this revolution, the poles are pointed directly at the sun and get almost 42 years of direct sunlight, while the other part of the planet is covered in total dark winter.
The second-least dense planet
Saturn is the least dense planet in our Solar System. In fact, Saturn has a lower mean density than water, so theoretically the whole planet would float in a pool that has a 60,000 km width. Uranus, with a mean density of 1.27 g/cm3 (slightly above water’s 1g/cm3) has the second-lowest density.
Uranus the ‘Ice Giant’
Uranus technically belongs to the Gas Giants, together with Jupiter, Saturn, and Neptune. However, Uranus is unique by having hydrogen mixed with a helium upper layer.
Below this layer is an icy mantle that surrounds Uranus’s ice and rock core. The planet’s pale blue color comes from its upper atmosphere, which is made of ammonia, water, and especially the crystalized methane ice.
Uranus is the coldest planet
While Neptune has a lower average temperature than Uranus, Uranus hits the coldest temperature of any planet at -224°C. This extremely low temperature also allows the formation of methane ice on Uranus’s upper atmosphere, which hides the storms underneath it.
Uranus has two sets of rings with 13 rings in total
Uranus has two outer rings and eleven inner rings. It is believed that these rings were formed when one or more of Uranus’s moons were broken up in collisions.
It is worth noting, that the last two of these rings were discovered as early as 2005, so it’s definitely possible that Uranus actually has more rings we haven’t discovered at the moment.
Uranus has 27 moons
Uranus has 27 moons in total orbiting it, not to count the ones that have been broken up into the 13 rings. Uranus’s moons are named after characters created by Alexander Pople and William Shakespeare, including Miranda, Titania, and Oberon.
Each of these moons is comprised of equal amounts of rock and ice, except for Miranda which is primarily made of ice. Ariel is Uranus’s brightest moon.
Only one spacecraft has flown by Uranus
The Voyager 2 spacecraft back in 1986 was the only spacecraft so far that has gone past the planet at a distance of 81,500 km.
Uranus may have an ocean of liquid diamond
Uranus is a very big planet, and due to its size and main molecular composition of methane, it is speculated that the very bottom layer of ice might be diamonds.
This is possible because the methane molecules break down under the very tough pressure of ice and liquid, releasing carbon which in turn will form diamonds.
So, it’s possible there’s actually a sea of liquid diamond with ice layers on Uranus.
Uranus was the first planet discovered by the modern telescope
Most of the planets in our Solar System are visible to the naked eye and ancient telescopes, so they were already known in ancient times.
Uranus, on the other hand, was the first planet discovered after the invention of the modern telescope, first recorded in 1690 by John Flamsteed.
It wasn’t until Sir William Herschel’s observation in 1781, however, that astronomers finally realized Uranus was a planet, not a start in the constellation Tauri.
You can learn more about Uranus here. Below, is a video by National Geographic that highlights some more interesting facts about Uranus.
Why Does Earth Rotate Counter-clockwise?
Now that we’ve learned that Venus and Uranus are the anomalies in how they rotate clockwise (and upside down for Uranus), why do our Earth and most of the other objects in our Solar System rotates counter-clockwise?
In fact, why do Earth and other planet rotate at all? As it turns out, this is not a phenomenon exclusive to our solar system, but in most observed stellar systems all throughout the universe.
With that being said, to better understand why our Earth rotates counter-clockwise instead of clockwise, we have to discuss the formation of our Solar System.
When our Solar System was beginning to form, smaller dust and gas particles began clumping together, forming a proto-star and smaller objects in the process. These smaller objects would then start orbiting the proto-star without any reason or pattern.
We can imagine over time, these small objects would collide with one another, dissolving most of them and leaving just those that moved in one similar direction.
The objects that broke apart would end up forming planetary rings, orbiting the proto-star in the same direction as the objects left behind.
After some time, objects from these rings would fall into the proto-star and begin clumping again, which will make the proto-star bigger with stronger gravitational force.
This proto-star will end up forming our Sun, while the other bits, over the years, began clumping together to form the planets, including Earth.
This cycle would repeat itself over and over again on a smaller and smaller scale, allowing smaller rings to form around the planets. These rings would then form the planet’s satellites, orbiting in exactly the same direction and orbital plane as the planets also orbit around the Sun.
Why do Planets Rotate at All?
There are actually many theories attempting to answer this question, but most experts believe the planets—including Earth—, most likely acquired their rotations due to collision.
It is believed that clumps of matter collided with the planets during the planets’ formation process around 4 billion years back.
Yet, collisions happen in random patterns, so how can most of them spin in the same direction?
Our Solar System, before its formation, was just an empty cloud of gas. What was likely to have happened is that a nearby big bang bounced up against this cloud of gas, collapsing it.
As the collapse happened, its own gravitational force caused to form a flat, spinning disk. This spinning disk happened to rotate counter-clockwise.
Since everything in our Solar System formed from this spinning disk, the rotational momentum also sent everything spinning in this same direction. Inertia, in turn, caused our planets to continue spinning in the vacuum of space.
In a vacuum, spinning objects maintain their direction and momentum of their spin since no external forces cause friction to stop them.
This is how the planets—including Earth—believed to acquire and maintain their spins.
What Would Happen if Earth Rotate Backwards?
If one day our planet starts rotating clockwise, that is east to west on its axis, it simply won’t be the Earth as we know it anymore.
The change of rotational direction will change so many things about our Earth. The Earth, although it’s difficult for us to notice it, spins very fast at 1,509 feet per second at the equator (460 meters/second).
When there’s a sudden change of direction, let’s assume the Earth suddenly moves the other way with similar speed, it will cause massive waves on the ocean and catastrophic winds.
These two conditions alone can simply wipe out everything above the ground.
However, what would happen if our planet’s rotational direction was reversed before us humans came into existence, millions of years ago just like Venus?
In this case, we would see the Sunrise in the west and set in the east, and the different rotational direction would generate entirely different climate conditions across all continents.
Iceland, for example, might be a desert instead of the land we know today.
If the earth rotates clockwise, however, one of the most important climate-driving current, the AMOC (Atlantic Meridional Overturning Calculation) would disappear from where it is today in the Atlantic Ocean, and another current should surface in the Pacific ocean.
This new current will be the main climate-driving force, responsible for distributing heat around the world.
As a result of this, we won’t have any deserts in Africa, and areas like Brazil should now have sand dunes and deserts.
The Amazon Rain Forest, for example, should now be a massive sand dune, and the southern part of the U.S. will now also have a lot of deserts.
However, none of these deserts would be anywhere close to the extreme dryness of the Sahara desert is today.
In general, there would be many more greens covering the planet, making the planet much healthier. However, countries like Russia would be much warmer.
Of course, these all are just theories, and there are also experts who think that the change of direction might turn our atmosphere to be too rich with oxygens, making them unlivable by humans.
There you have it, everything you need to know about what planets in our solar system rotate clockwise. If you enjoyed this article, be sure to check out some of our other great articles below.