Scientists from the University of California, Los Angeles, irradiated Venus with radio waves for 15 years and received the reflected signal. As a result, were able to calculate the duration of the day on the planet as accurately as possible. It turned out that it always changes by at least 20 minutes because of the massiveness of the planet's atmosphere.
On average, a day on Venus lasts 243.0226 Earth days, which is almost eight months. The planet's rotation speed is not constant because the atmosphere exchanges a large number of impulses with the solid surface of the planet. They either speed up or slow down Venus.
Similar processes also take place on Earth, but we do not notice them. The effect of the atmosphere subtracts or adds only one millisecond from or to the day.
The situation on Venus is more dramatic because its atmosphere is 93 times heavier than Earth's. It is 96% carbon dioxide and 3.5% nitrogen. The pressure on the planet's surface is equivalent to that of the ocean at a depth of 900 meters.
Calculating the length of the day is important for future space missions. Due to the difference in 20 minutes, the devices can land 30 kilometers from the planned location.