![]() While the Moon is revolving around the Earth, the Earth revolves around the Sun. How does this happen? The reason is not very hard to understand. However, the time between two New Moons is around 29 and a half days. We have just said that the Moon completes one revolution around the Earth in 27 days and 8 hours. This is because the Earth is round and our horizon changes if we go to the north or the south. In other words, the northern observer sees the Moon at a lower place in the sky, while the southern one sees the Moon at a higher place in the sky. On the other hand, the place where we see the Moon in the sky depends on our parallel on the Earth. Because of this huge difference, we see almost the same shape of the Moon anywhere in the world- this “almost” will cause many problems, when we determine the dates in lunar calendar. While the closest distance of the Moon to the Earth is around 350 thousand kilometers, the diameter of the Earth is around 13 thousand kilometers. As the figures below suggest, the distance from the Moon to the Earth is much greater than the diameter of the Earth. ![]() One might ask then why do we see the Moon as the same shape throughout the night. The Moon’s position does not change greatly in one day relative to that of the Earth, but the Earth’s rotation around itself changes our position a great deal. The position of the Moon with the Earth according to sunlight determines how we see the Moon. For simplicity, the sunlight is fixed, but this is not a problem as the Earth and the Moon are revolving around the sun together. In the picture below, we see the phases of the Moon. Because of this, we always see the same side of the Moon. At the same time, while revolving around the Earth, the Moon rotates around itself. It takes about 27 days and 8 hours for the Moon to complete one revolution around the Earth. The starting date of a month in the Islamic lunar calendar is very important in the Islamic world as it determines the essential religious days, like the first and last days of fasting, and Muslim holidays. Since the Islamic lunar year has 12 lunar months, it is on an average 11 days shorter than the Gregorian year the Islamic year shifts by about 11 days to an early date according to the Gregorian calendar. There are 12 months in an Islamic year, which is either 354 days or 355 days long, compared to the Gregorian calendar year of 365 or 366 days. ![]() Hence, the month is either 29 days or 30 days. The Islamic calendar is based on lunar months, which begin when a new crescent is sighted in the western sky after sunset within a day or so after the New Moon. ![]()
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