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.
Itâs estimated that three billion years ago, a day zipped by in about 13 hours, while now one full rotation of the Earth on its axis takes 23 hours, 56 minutes and 4.091 seconds. Old theories held that the effect was gradual, with the length of an Earth day increasing just .002 seconds per century.