Why is the lunar month longer than the number of days it takes to orbit the earth?

Answer 1

Because the Moon orbits the Earth whereas the Sun and stars do not. So the Moon has real motion apart from what the rotation of the Earth appears to give it. Thus the Moon rises in the East about 20 minutes sooner every day.

Answer 2

The Earth takes 23 hours, 56minutes and 4.091 seconds to complete one spin or "sidereal day". This is the rotational period relative to the background stars, slightly short of the 24 hour "mean solar day". This is due to the time difference caused by Earth's progression around the Sun in that time. In one day, the Earth has moved around the Sun a little more, so an extra few minutes of spin are required for the Sun to appear in the same place in the sky as one day previously.

Usually the solar day is indeed longer than the sidereal day, but not for all planets.

For Venus the sidereal day is longer, because Venus rotates in the opposite direction to its orbital revolution. This is called "retrograde" rotation.

Also, because Venus rotates very slowly there is a huge difference in the length of the two "days".

Answer 3

definition of month-[ calendar month is also known as simply month]

1. the period (synodic month) marked by two successive lunar conjunctions with the sun, equal on the average to 29.53 days: also called lunar month

definition of lunar month-

The average time between successive new or full moons, equal to 29 days, 12 hours, 44 minutes. Also called synodic month.

Answer 4

The duration of an orbit around the Earth is determined by the distance to Earth. At the (average) distance the Moon is circling, it completes an orbit every 27 days or so. However, the Lunar Month is determined by a complete traverse through all the phases of the Moon. And it takes two days longer for the Moon to go through all its phases, because while the Moon is completing its orbit, the Earth-Moon system will have moved along its orbital path around the Sun, meaning the Moon is being lit by the Sun from a different angle.

Answer 5

That depends what calendar you are talking about. Both the Jewish and the Islamic (or Hijri) calendars have calendar months that coincide with the lunar cycle - that is, with the lunar month. But you are probably more familiar with the Gregorian Calendar - in this case, the months are slightly longer than the lunar months. A lunar cycle is about 29.5 days; the months in the Gregorian calendar have almost 30.5 days on average.

Answer 6

A sidereal month, which is about 27.32 days, is the time it takes the moon to complete one full orbit of Earth as measured by the time between subsequent monthly alignments of Earth, the moon, and a distant "fixed" star. A synodic month, which is about 29.53 days, is the time of a complete cycle of the lunar phases. It can also be described as the time between subsequent alignments of the sun, earth and moon. Since a sidereal month is about 1/13 of a year, by the time a lunar orbit is completed Earth has advanced about 1/13 of its way around the sun. Therefore, to return to the same lunar phase the moon must complete about 1 1/13 orbits of Earth.

Imagine you are timing synodic months from full moon to full moon. At the time of the full moon Earth is roughly right between the sun and the moon. After six months the earth-moon system is on the opposite side of the sun. Earth is still between the sun and the moon after six full synodic months, but since the reference for sidereal months is a distant star, the moon is between the sun and the earth after six full sidereal months (roughly). If a solar year were exactly 12 synodic months long, it would also be exactly 13 sidereal months long.

Answer 7

A lunar year is slightly shorter than a solar year. A lunar year has about 354 days while a solar year has 365.

Answer 8

Yes.