What is the revolving period of Venus?
In order to find the rotation of a planet, near daily information should be taken of a planet through an intense telescope capable of following a specific reference point on a planet. This works for most planets except Venus, which has such a dense atmosphere that it is impossible to see any surface structures through the thick acid clouds. To find the rotational speed of the planet Vesto Slipher, an American born astronomer, used spectroscopy which allowed him to see how light was filtered through the atmosphere and found that the rotation was extremely slow, shorter in fact than the time it took to orbit once around the Sun! Later in the 1970's NASA sent probes to the surface that were able to "see" the surface using radio waves and even one that could land on the surface of the planet. This last probe found our now accepted rotational speed for Venus of 243.02 Earth Days, the slowest of any planet in our solar system.
Another great way to learn more about Celestial bodies is to check NASA websites or books at your local library. NASA is a wealth of knowledge when it comes to different stars, planets, and other space structures.