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.
The period of revolution is called the year, and equals about 365.2426 days. The Calendar and Leap Years. The Earth takes approximately 365 days and six hours to revolve around the Sun. The extra six hours accumulate into an entire day every four years, so that a leap year will contain the extra 366th calendar day. The extra day is added as February 29 which only exists in a leap year.