It happens because the Moon's orbit is tilted relative to the Earth's orbit, so at Full Moon the Moon actually passes above or below the point where it is exactly in line with the Sun and Earth.
For an eclipse to happen the Moon has to be in a special part of its orbit where its own orbit crosses the plane of the Earth's orbit. The point where it crosses over is a node, and it passes an ascending node and a descending node every time it goes round.
It happens every month, but that does not mean in the same place. Lunar eclipses happen twice a year in a 1-2 month period.
When the conditions are right, a lunar eclipse can happen in ANY month, but only at the time of Full Moon.
one month
Solar and lunar eclipses don't occur every month because the plane of the Moon's orbit around the Earth is not aligned with the plane of the Earth's orbit around the Sun.The Moon's path is tilted when compared to the plane of Earth's orbit, so the Moon is not in a direct line with the Sun and Earth. In a solar eclipse, the Moon must be directly between the Sun and the Earth. Similarly, in a lunar eclipse (slightly more frequent), the shadow of the Earth has to fall on the Moon.
The moon's path around the Earth is related to when an eclipse happens. Most of the time the path of the orbit is a tad above or a tad below the line connecting the Earth and the Sun. Hence no eclipse. There is however a shadow cast by the moon, we are just not in a position to be in the shadow. So when circumstances happen that the path of the orbit of the moon intersect the straight line between the Sun and the Earth we get an Eclipse of Sun or Moon if the path of the Moon's orbit takes through the Earth's shadow.
why does a lunar or solar eclipse not occurs every month?
It happens every month, but that does not mean in the same place. Lunar eclipses happen twice a year in a 1-2 month period.
Lunar eclipses can happen a maximum of twice per year, and only at the time of the full moon. Sometimes the alignment is just right, and we get a total lunar eclipse. If the alignment isn't exact, we might get a partial or a penumbral eclipse instead of a total eclipse.
When the conditions are right, a lunar eclipse can happen in ANY month, but only at the time of Full Moon.
because it takes a while for the moon to come right im between the sun and earth in the solar eclipse.
The first of a lunar month.
one month
Eclipses do not happen every month because the Moon is in an orbit that is inclined to the plane of the Earth's orbit, the ecliptic. So although the Moon passes behind the Earth (as seen from the Sun) every month, it usually passes above or below the Earth's shadow. For a lunar eclipse, Full Moon has to occur when the Moon is crossing the ecliptic, when it is said to be at a node.
A solar eclipse doesn't occur every 28 days because the moon's orbit is tilted compared to the earths.
Solar and lunar eclipses don't occur every month because the plane of the Moon's orbit around the Earth is not aligned with the plane of the Earth's orbit around the Sun.The Moon's path is tilted when compared to the plane of Earth's orbit, so the Moon is not in a direct line with the Sun and Earth. In a solar eclipse, the Moon must be directly between the Sun and the Earth. Similarly, in a lunar eclipse (slightly more frequent), the shadow of the Earth has to fall on the Moon.
Its December 31st 2009, there is no lunar eclipse for me. But there is a Blue Moon. 2nd full moon of the month... and It is big and bright tonight.
Generally, a lunar eclipse happens _about_ every 6 months - or, to be more precise, every 6 full moons, which isn't exactly the same thing. Sometimes there are two partial lunar eclipses a month apart rather than one total lunar eclipse, but on average, every 6 months or so. You can see the catalog of all eclipses from 2000 BCE to 3000 AD on the NASA Eclipse Web Site at the link below.