A day on Venus is longer than its year — the planet turns so slowly, and backwards, that the Sun rises in the west and takes about 58 Earth days to cross the sky
The planet’s backwards rotation and glacial spin create a cosmic paradox: sunrise comes in the west, and the Sun takes longer to cross the sky than Venus takes to orbit the Sun
A day on Venus is longer than its year — the planet turns so slowly, and backwards, that the Sun rises in the west and takes about 58 Earth days to cross the sky
An artistic rendering of cloud-covered Venus. Image by Zelch Csaba via Pexels.
Venus keeps time in a way that seems almost designed to confuse. The planet takes about 243 Earth days to turn once relative to the distant stars, yet it completes an orbit around the Sun in only about 225 Earth days. In that specific sense, a day on Venus really is longer than its year.
Its rotation is also retrograde, opposite to the direction in which Venus travels around the Sun and opposite to the spin of most planets. From the surface, the Sun would therefore rise in the west and set in the east.
There is one important numerical distinction. The 117-day figure often attached to this fact is the full solar day, from one sunrise to the next, not the time taken for the Sun to travel from horizon to horizon. A notional sunrise-to-sunset passage lasts about half as long, or roughly 58 Earth days.
Venus has two different kinds of day
On Earth, the difference between the two common meanings of “day” is small enough to overlook in ordinary conversation. A sidereal day measures one rotation relative to the distant stars. A solar day measures the interval required for the Sun to return to the same position in the local sky.
Those clocks diverge dramatically on Venus. A NASA planetary fact sheet gives the planet’s retrograde rotation period as 243.02 Earth days, its orbital period as 224.70 days and the interval between successive sunrises as 116.75 days.
The famous comparison between the Venusian day and year refers to the first of those values. One turn relative to the stars takes longer than one circuit of the Sun. But a person counting apparent sunrises would experience nearly two solar days during each Venusian year.
Backward rotation makes the solar day shorter
Venus travels around the Sun in the same broad direction as most planets, but its surface rotates the other way. As a result, its orbital motion and rotation work together when determining the Sun’s apparent passage through the sky. The Sun returns to the same local position after about 116.75 Earth days, well before the planet has completed a 243-day turn relative to the stars.