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 time, the solar day, during which the earth makes one complete revolution on its axis relative to the sun. The mean solar day is the average length of the apparent solar day and is some four minutes (3 minutes 56.5 seconds of sidereal time) longer than the sidereal day.