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.
Earth's rotation period relative to the Sun (its mean solar day) consists of 86,400 seconds of mean solar time, by definition. Each of these seconds is slightly longer than an SI second because Earth's solar day is now slightly longer than it was during the 19th century, due to tidal deceleration.