2 Measuring vitamin D levels is also expensive, costing between $50 and $220 per test in commercial laboratories for patients without insurance. Another challenge is that the level of 25-hydroxy-vitamin D that should be considered normal is unclear.
The closer a planet is to the sun, the shorter the time to complete one revolution is. Mercury, for example, has an orbital period of 88 days while it takes Jupiter about 11.86 years. The period of the Earth's orbit is usually thought to be 365 days as calendars show. However when averaged it is actually about 365.25 days, which requires an extra day on the calendar every four years (causing a leap year). Contradictions within orbit times are probably caused by the ages of the sources.
1 Whereas Earth rotates in about 24 hours Venus rotates in the contrary sense (retrograde rotation) in 243 days. 2  The orbital period of Venus is 225 days so that a Venus year takes less than a full day. The combination of these two periods results in the Sun appearing from the West and dissapearing over the East with a day-night cycle of 117 days. 2  The atmosphere of Venus is 90 times more dense than that on Earth and it is made of 96.5% of CO2 and a 3% of nitrogen.