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.
When the conditions are right, a lunar eclipse can happen in ANY month, but only at the time of Full Moon.
one month
A lunar eclipse can occur multiple times a year, but the frequency can vary. On average, there are about two to four lunar eclipses each year. Lunar eclipses can be partial, total, or penumbral, with total eclipses being less common.
because it takes a while for the moon to come right im between the sun and earth in the solar eclipse.
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?
A lunar eclipse doesn't happen every month because the Moon's orbit is tilted relative to Earth's orbit around the Sun. This means that most of the time, the Moon passes above or below Earth's shadow, so a lunar eclipse only occurs when the alignment is just right.
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.
because it takes a while for the moon to come right im between the sun and earth in the solar eclipse.
When the conditions are right, a lunar eclipse can happen in ANY month, but only at the time of Full Moon.
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.
one month
The first of a lunar month.
A lunar eclipse can occur multiple times a year, but the frequency can vary. On average, there are about two to four lunar eclipses each year. Lunar eclipses can be partial, total, or penumbral, with total eclipses being less common.
A solar eclipse doesn't occur every 28 days because the moon's orbit is tilted compared to the earths.
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.
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.