[inquest]

After 153 days, the Venus Express will begin to orbit Venus and will remain in orbit for 500 terrestrial days, which corresponds to just two Venusian days (one day on Venus equals 243 Earth days).

Actually, properly defined, a day on Venus (sunrise to sunrise) is about half that length of time. It takes Venus 243 earth days to complete a rotation, but it also takes that roughly that same length of time (moving in the other direction) to complete a circuit around the sun. Putting those data together cuts the number in half.

[Constantine XIII]

For Venus, the difference between the siderial day the solar day is important.