As can be seen in
Karla's wu above, the planet Venus has
rotation time of over 243 days, meaning that this is the length of day on Venus. That means that the nights are about 60 days long, which can be compared to the constant days/nights within the
polar circles on
Earth. Of course, no one lives on Venus anyway.
Anyhow, the interesting thing about Venus's rotation is that it is retrograde, meaning that it spins the other way compared to most other planets, Earth included. This means that the (about) 20 days long sunrise takes place in west. Except that the sun rarely penetrate the heavy clouds over the planet.
It has long been a mystery why Venus rotates the "wrong" way. The slow days are believed to be due to the heavy gravitational pull from the sun; the innermost planet Mercury only have 3 days on every revolution of the sun - Mercury-year, that is.
When it comes to the direction of the spin, researchers thought that the planet might have flipped upside down at one time, so that it now rotates the same way as Earth, only upside down... But recently a French team at Institute Astronomie et Systemes Dynamiques of researchers published a work that suggest that Venus did not flip, but stop. The rotation was slowed until it stopped and started rotating the other direction, much like Earth's rotation is slowing a few seconds every 100,000 years.
The reasons for the slowing rotations could be, apart from the heavy pull from the sun, tidal waves that resulted from Sun's gravitation as well. Friction between the planet's mantle and core, as well as tidal effect from other planets may play a part. The study concludes that the rotation axis of Venus only have four stable states, two in each direction, and that the retrograde states are more stable.
Source: Scientific American