It took 15 years of very accurate radio observations, but astronomers have now obtained a very good measure of how fast Venus rotates, which means we know how long a day is on Earth’s burning twin. A Venusian day corresponds to 243.0226 Earth days – approx. two thirds of an earth year – and it changes with a variation of approx. 20 minutes. The results are reported in Nature Astronomy.
It may seem surprising that we did not know the exact length of a day’s Venus, given that the planet is relatively adjacent. It is easy to calculate the rotational speed of most planets if they have identifiable functions on the surface. The gas giants are tougher, but luckily Jupiter has a giant red swirling storm to track. Venus̵
Between 2006 and 2020, astronomers used the 70-meter-wide Goldstone antenna in California’s Mojave Desert to send radio waves to Venus. These waves can move through the atmosphere and are then reflected from its surface. Several minutes later they are picked up again at the Goldstone Observatory and then approx. 20 seconds later at the Green Bank Observatory in West Virginia. The exact difference between the two detections tells the team how fast the planet rotates.
“We use Venus as a giant disco ball,” UCLA lead author Jean-Luc Margot said in a statement. “We illuminate it with an extremely powerful flashlight – about 100,000 times brighter than your typical flashlight. And if we trace the reflections from the disco ball, we can derive properties of spin [state]. ”
The experiment sounds much easier than it is in real life. Earth and Venus must be in the correct configuration for it, and the two radio observatories must work for the observations to succeed. Twenty-one observations were eventually taken over the 15-year period.
“We found that it is actually challenging to make everything work equally well for a period of 30 seconds,” Margot said. “Most of the time we get some data. But it is unusual that we get all the data that we hope to get. ”
The variation in the length of the day is due to the movement of the dense atmosphere of Venus. At the surface level, the pressure is about 93 times higher than on Earth, so its skew affects the planet’s spin.
The observations also revealed more about Venus. The team was able to estimate that the core of the planet is approx. 3,500 kilometers (2,175 miles) wide. This is the same size as Earth’s own. However, based on current knowledge, we do not know if it is liquid, solid or a mixture.
The research also provides a better measurement of the axial inclination relative to the planet’s orbital plane. They found Venus tips to one side at exactly 2.64 degrees, an improvement over previous estimates by a factor of 10 in precision. Given the minute angle, the planet does not experience seasons. The Earth’s inclination is about 23 degrees, very different from the much smaller Venusian inclination. But Venus is unique among the planets as it spins in the opposite direction, giving some strange effects.
Timing on Venus is very strange. A rotation of the planet takes 243 days, but its year (revolution around the sun) is only 225 days. But due to spinning in the opposite direction, if we count a day just from dawn to dawn, it would only last 117 days. No wonder this strange planet continues to hide so many mysteries.
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