Portuguese 
English 
Spanish 
6 min of reading 
0 comments 
Venus takes 243 Earth days to complete a rotation on its own axis, but only 225 to orbit around the Sun. According to Olhar Digital, this temporal inversion makes it the planet with the longest day in the Solar System and one of the most intriguing celestial bodies for modern astronomy, with a dense atmosphere, temperatures capable of melting lead, and a retrograde rotation that defies earthly logic.
Venus is, among all the planets in the Solar System, the one that most challenges the human notion of time. A single rotation on its own axis takes exactly 243.0226 Earth days, according to a study published in the journal Nature Astronomy by the team of astronomer Jean-Luc Margot from the University of California, Los Angeles. The data was obtained over 15 years of measurements with radio waves transmitted by the Goldstone Antenna of the NASA in the Mojave Desert. The result confirmed something that has intrigued scientists for decades: on Venus, a day is longer than a year.
The Venusian year, which corresponds to the time of a complete orbit around the Sun, lasts about 225 Earth days. In other words, Venus completes a full orbit around the star even before it finishes rotating on itself. This mismatch between rotation and translation makes the planet a unique case among the known rocky worlds and raises fundamental questions about how gravitational forces and the atmosphere itself can alter the behavior of a celestial body over billions of years.
Why Venus rotates so slowly
The explanation for the extreme slowness of Venus’s rotation is still a subject of debate among astronomers, but the most accepted hypotheses combine two factors. The first is the gravitational tide exerted by the Sun, which over billions of years tends to slow down the spin of nearby planets. The second is the influence of Venus’s own atmosphere, which is extraordinarily dense and composed of more than 96% carbon dioxide, with surface pressure about 90 times greater than Earth’s.
-
White hydrogen found in billion-year-old rocks in Canada impresses researchers, can generate energy for hundreds of homes, and opens a new race for clean fuel hidden underground.
-
The macabre discovery by archaeologists in an Asian forest: a giant jar in Laos reveals human bones from various generations about 1,200 years old.
-
The popular fermented food can help eliminate microplastics from the body.
-
The ITER project gathered 10 million components manufactured in 35 countries to create an “artificial star” in France that will heat plasma to 150 million degrees Celsius, a temperature ten times higher than that of the Sun’s core, and attempt to reproduce for the first time in a laboratory the reaction that has fueled stars for billions of years.
This thick atmosphere generates what scientists call a thermal atmospheric tide. Solar heating creates pressure differences that exert torque on the planet, gradually altering its rotation speed. Climate models indicate that this interaction between atmosphere and surface has been able to slow down Venus over geological eras, resulting in the slowest rotation of any planet in the Solar System. At the equator, Venus’s surface rotates at only 6.5 kilometers per hour — compared to Earth’s 1,670 kilometers per hour.
The retrograde rotation that makes the Sun rise in the west
Venus not only rotates slowly — it rotates in the opposite direction to most other planets. While Earth and almost all its neighbors rotate from west to east, Venus does the opposite. This means that, seen from the Venusian surface, the Sun would rise in the west and set in the east, in a scenario that completely reverses the experience of any observer accustomed to Earth’s patterns.
The cause of this retrograde rotation is also not fully resolved. One of the most discussed theories suggests that a massive collision during the formation of the Solar System may have drastically inverted Venus’s axis. The planet has an axial tilt of 177 degrees, which in practice means it is almost upside down. Another hypothesis suggests that the combination of solar tide effects and atmospheric interactions may have slowed and reversed the rotation over billions of years, without the need for a major impact.
Sidereal day, solar day, and the confusion of calendars
To understand Venus, it’s necessary to distinguish between two types of day. The sidereal day measures the time it takes for the planet to complete a rotation relative to the fixed stars — and this is the period of 243 Earth days. The solar day measures the interval between two consecutive passages of the Sun over the same point in the sky, which on Earth corresponds to the 24 hours we know.
On Venus, the combination of slow rotation with retrograde movement produces a peculiar effect: the solar day lasts about 116.75 Earth days, a value shorter than the sidereal day. This happens because the rotation opposite to the orbit makes the Sun “advance” faster in the Venusian sky than if the rotation were in the same direction. The result is that a year on Venus is equivalent to approximately 1.92 Venusian solar days — that is, in one year, the planet experiences less than two complete cycles of day and night.
The atmosphere that rotates 60 times faster than the planet
If Venus’s rotation is absurdly slow, the planet’s atmosphere compensates with a surprising speed. The phenomenon is known as atmospheric super-rotation: the upper layers of the atmosphere complete a full rotation around Venus in just four Earth days, moving about 60 times faster than the surface below them.
This discrepancy between atmospheric speed and planetary rotation is one of the great mysteries of planetary science. No model has been able to fully explain why Venus’s atmosphere behaves this way. The phenomenon generates winds of up to 360 kilometers per hour in the upper layers and makes direct observation of the surface difficult, as dense clouds of sulfuric acid block the view. It was precisely because of this barrier that UCLA researchers had to use radio waves to measure the planet’s rotation — a method that Margot compared to illuminating Venus like a giant disco ball.
The hell that makes everything even more extreme
The temporal peculiarities of Venus gain another dimension when combined with the surface conditions. The average temperature reaches 465 degrees Celsius, making it the hottest planet in the Solar System — even surpassing Mercury, which is closer to the Sun. This extreme heat does not come from proximity to the star, but from the uncontrolled greenhouse effect caused by the dense carbon dioxide atmosphere.
The atmospheric pressure on the surface is equivalent to that found 900 meters deep in Earth’s oceans. Clouds laden with sulfuric acid permanently cover the planet. Soviet probes from the Venera program managed to land on Venus between the 1970s and 1980s, but none survived for more than two hours in the surface conditions. Venus is, at the same time, the planet most similar to Earth in size and the most radically different in habitability — a paradox that astronomers often summarize by calling it the “evil twin” of our planet.
What Venus teaches about other worlds
The scientific interest in Venus goes beyond curiosity. Understanding why a planet so similar to Earth in mass and size became so different is essential for assessing the habitability of exoplanets in other star systems. There are probably billions of planets with characteristics similar to those of Venus in the Milky Way, as noted by Professor Margot in his research.
Future missions like NASA’s VERITAS and DAVINCI, and the European Space Agency’s EnVision, are planned to study Venus with unprecedented depth in the coming decades. The objectives include mapping the surface with high-resolution radar, analyzing atmospheric composition, and investigating whether the planet ever had liquid oceans at some point in the past. Venus remains a key piece for understanding the fate of rocky worlds and a reminder that, in the universe, the rules we know on Earth do not always apply.
Did you know that a day on Venus lasts longer than an entire year? Which aspect of this planet surprises you the most, the reverse rotation, the infernal heat, or the atmosphere that spins 60 times faster? Tell us in the comments.
Be the first to react!