Venus
Earth's twin in size and mass, and in nothing else at all. The planet itself, turning at its real rate — how big and how heavy, how long its day and its year, and what is still unexplained.
Venus on its axis
Turning here at one rotation every 12 seconds, which is 1,749,750 times real speed. What is not sped up: which way it turns — backwards, and that is real, how far the axis leans, and how its day compares with every other planet's. An unbroken cloud deck, which is what you would actually see: no telescope at any wavelength the eye uses has ever seen the ground through it. The famous dark Y is an ultraviolet feature and is deliberately not drawn here — this is the visible-light view, and in visible light Venus is very nearly blank.
Venus has no moons, so there is no system of its own to watch here — the globe above is the planet itself, turning at its real rate. To see where it is in the solar system today, and how fast it goes round compared with everything else:
Venus by the numbers
The mass is worked out from Venus’s gravitational parameter and the gravity from that and its radius; the year comes from Kepler’s third law and the width is the same figure the simulator draws with. None of them is typed in beside the picture, so none of them can disagree with it.
When Earth and Venus are next closest
Both planets are moving, so the gap between them swings enormously — and the closest approaches are not all equal, because the orbits are ellipses rather than circles. These are the next four, solved from the orbits rather than looked up.
Click a date to take the simulator there. These are minimum-distance moments, which fall near — but not exactly on — opposition.
Venus: things worth knowing
- Venus turns backwards, and so slowly that its day is longer than its year: 243 Earth days to rotate once, 225 to go round the Sun.
- The surface pressure is what you would feel 900 m underwater on Earth. The first landers survived between 23 minutes and about two hours before being crushed and cooked.
- It is hotter than Mercury even though it is nearly twice as far from the Sun. That is the greenhouse effect, and Venus is the reason we know how far it can go.
- The atmosphere super-rotates: the cloud tops circle the planet in about four days while the planet underneath takes 243. Nothing on Earth does anything like this.
- Almost the whole surface is between 300 and 600 million years old, which for a planet is suspiciously uniform — it suggests the crust was resurfaced globally rather than gradually.
What we still don’t know about Venus
Every one of these is genuinely unsettled — not simplified for the page, not waiting on a textbook update.
Why does it spin backwards, and so slowly?
Either a giant impact flipped it, or the thick atmosphere did it: solar tides in an atmosphere that heavy, working against friction between core and mantle, can in principle turn a planet over and stall its spin without hitting it. The two histories are hard to tell apart from the outside, and the answer decides whether Venus was violently rearranged or just slowly wound down.
Did Venus ever have oceans?
Its deuterium-to-hydrogen ratio is about 150 times Earth's, which is the signature of a planet that has lost an enormous amount of ordinary water to space. How much, and when the last of it went — early, or as recently as a billion years ago — is unresolved, and the answer changes whether Venus was ever habitable.
Is anything happening in the clouds?
A 2020 claim of phosphine in the cloud deck, where the temperature is mild even though the surface is not, has been argued about ever since; later observations have both supported and failed to reproduce it, and there is no accepted abiotic or biological explanation. Treat it as an open measurement question, not as a discovery.
Recently learned about Venus
Findings reviewed August 2026. Space science moves; a date on a finding is part of the finding.
The rest of the system
Inward: Mercury. Outward: Earth. Or step out: all the planets, a picture and a paragraph each, and the solar system simulator, where every orbit runs at once.
The other simulator
This one is about the whole system. If the question is where the sun and the moon are from where you are standing — what time the sun comes up, why tonight's moon is the shape it is — that is the Sun, Earth & Moon movement simulator, which has a page for every city and a slider over a day, a week or a month. Between the two is the three bodies moving together — Earth going round the sun, the moon going round the Earth, on one screen and openly not to scale, keeping only the real ratio between the two periods.
And for why any of it stays up: the orbital velocity simulator takes one planet and lets you set its distance and its sideways speed by hand, so you can watch the balance that holds every orbit here — and break it, into an ellipse, an escape, or a fall into the sun.
Also: the classroom guide · sunrise & sunset by city · moon phase & moonrise · lunar eclipses · how the positions are worked out
Venus: questions without settled answers
Why does it spin backwards, and so slowly? Either a giant impact flipped it, or the thick atmosphere did it: solar tides in an atmosphere that heavy, working against friction between core and mantle, can in principle turn a planet over and stall its spin without hitting it. The two histories are hard to tell apart from the outside, and the answer decides whether Venus was violently rearranged or just slowly wound down.
Did Venus ever have oceans? Its deuterium-to-hydrogen ratio is about 150 times Earth's, which is the signature of a planet that has lost an enormous amount of ordinary water to space. How much, and when the last of it went — early, or as recently as a billion years ago — is unresolved, and the answer changes whether Venus was ever habitable.
Is anything happening in the clouds? A 2020 claim of phosphine in the cloud deck, where the temperature is mild even though the surface is not, has been argued about ever since; later observations have both supported and failed to reproduce it, and there is no accepted abiotic or biological explanation. Treat it as an open measurement question, not as a discovery.