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 earth is the third planet from the sun. To most people the period of rotation of the earth is 24 hours, but the actual value is 23 hours 56 minutes and 4 seconds. This happens because a solar day is longer than a sidereal day. While the earth rotates, it also moves around the sun in the interval from one day to another.