Venus

A greenhouse gone catastrophically wrong

Venus is almost exactly Earth's size, and it may once have been more Earth-like, perhaps even with oceans. But it fell into a runaway greenhouse: its atmosphere, now more than 96% carbon dioxide, traps the Sun's heat so effectively that the surface sits at about 465 °C — hot enough to melt lead, and hotter than Mercury despite being nearly twice as far from the Sun. The air is crushingly dense, about 90 times Earth's pressure (like being 900 meters underwater), and the planet is wrapped in permanent clouds of sulfuric acid. Spacecraft that have landed survived only minutes.

Venus is also a planet of oddities. It spins backwards (retrograde) and so slowly that a single rotation takes 243 Earth days — longer than its 225-day year, meaning a Venusian "day" outlasts its "year." Beneath the clouds, radar reveals a volcanic world of vast plains, highland "continents," and thousands of volcanoes, some of which may still be active today.

The brightest star that isn't a star

Venus is the easiest planet to find and the most dazzling — after the Sun and Moon, it is the brightest object in the sky, bright enough to cast faint shadows and to be seen in broad daylight if you know where to look. It never wanders far from the Sun, so it appears either in the west after sunset (the "evening star") or in the east before dawn (the "morning star"), blazing so brilliantly that it is regularly reported as a UFO.

Point a small telescope at it and you'll see something Galileo found revolutionary: Venus shows phases, from a small "full" disc when it's on the far side of the Sun to a large, thin crescent when it swings near Earth. Those phases were direct evidence that Venus orbits the Sun, not the Earth — a key blow for the Sun-centered model. You won't see surface detail (the clouds hide everything), but the changing crescent over weeks is a genuine pleasure.

Two "stars" that are one, and a twin that's a hell

For much of history people believed the brilliant morning star and the brilliant evening star were two different objects — the Greeks even gave them separate names, Phosphorus and Hesperus. They are one and the same: Venus, seen on either side of the Sun. The other lasting misconception is that Venus is Earth's twin. It is a twin only in size; in reality it is the least hospitable major world we know — an acid-clouded oven where nothing we recognize as life could survive. If anything, Venus is a warning of how badly a greenhouse can run away.

Fittingly for the sky's most beautiful object, Venus is named for the Roman Venus, goddess of love and beauty. Her Greek counterpart is Aphrodite, born from the sea foam — and Venus is the only planet named for a female deity, its radiance matched to the goddess it honors.

Step into the Greek myths written across the night sky →