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.
This is the time it takes Earth to rotate 65.27 cm (25.70 in), as measured at the equator. On average, a mean solar day in the last 365 days was 1.21 ms over 24 hours, so today's day length is above average. Over this period, 140 days have been longer than today, while 226 have been shorter than today. If every day was as long as today, a leap second would have to be added every 712.61 days.