This view of the Moon's orbit helps to explain why you don't get a lunar eclipse every full moon, but only about every six months when the Earth, Moon and Sun line up on the line of nodes.
http://hyperphysics.phy-astr.gsu.edu/hbase/Solar/lunecl.html
However we know that if an eclipse occurred at some moment, then there will occur an eclipse again S synodic months later, if that interval is also D draconic months, where D is an integer number (return to same node), or an integer number + ½ (return to opposite node).
https://en.wikipedia.org/wiki/Eclipse_cycle
Eclipses (up to three) occur during an eclipse season, a one-or two-month period twice a year, around the time when the Sun is near the nodes of the Moon's orbit. An eclipse does not occur every month, because one month after an eclipse the relative geometry of the Sun, Moon, and Earth has changed.
https://en.wikipedia.org/wiki/Eclipse_cycle
A lunar eclipse occurs when the Moon passes directly behind the Earth into its umbra (shadow). This can occur only when the sun, Earth and moon are aligned (in  syzygy ) exactly, or very closely so, with the Earth in the middle.
https://en.wikipedia.org/wiki/Lunar_eclipse
Hence, a lunar eclipse can occur only the night of a full moon. The type and length of an eclipse depend upon the Moon's location relative to its orbital nodes. A total lunar eclipse has the direct sunlight completely blocked by the earth's shadow. The only light seen is refracted through the earth's shadow. This light looks red for the same reason that the sunset looks red, due to rayleigh scattering of the more blue light.
https://en.wikipedia.org/wiki/Lunar_eclipse
Eclipses may occur repeatedly, separated by certain intervals of time: these intervals are called eclipse cycles. The series of eclipses separated by a repeat of one of these intervals is called an eclipse series.
https://en.wikipedia.org/wiki/Eclipse_cycle
An eclipse can only occur when the Moon is close to the plane of the orbit of the Earth, i.e. when its ecliptic latitude is small. This happens when the Moon is near one of the two nodes of its orbit on the ecliptic at the time of the syzygy.
https://en.wikipedia.org/wiki/Eclipse_cycle
Lunar Eclipse. A lunar eclipse occurs when the Earth's shadow falls on the Moon, and a solar eclipse occurs when the Moon's shadow falls on the Earth. A look at the geometry of Moon phases would make it appear that a lunar eclipse should happen at every full moon and a solar eclipse at every new moon. This does not occur because the plane of the Moon's orbit is tilted 5.2° with respect to the plane of the Earth's orbit around the Sun (the ecliptic plane).
http://hyperphysics.phy-astr.gsu.edu/hbase/Solar/lunecl.html
The best known eclipse cycle, and one of the best for predicting eclipses, in which 223 synodic months equal 242 draconic months with an error of only 51 minutes. It is also close to 239 anomalistic months, which makes the circumstances between two eclipses one saros apart very similar.
https://en.wikipedia.org/wiki/Eclipse_cycle
A partial lunar eclipse occurs when only a portion of the moon enters the umbra. When the moon travels completely into the Earth's umbra, one observes a total lunar eclipse. The moon's speed through the shadow is about one kilometer per second (2,300 mph), and totality may last up to nearly 107 minutes.
https://en.wikipedia.org/wiki/Lunar_eclipse
when do lunar eclipse happen
Lunar Eclipse happens when the Moon passes directly behind the Earth into its umbra. A lunar eclipse happen when the Moon passes directly behind the Earth into its umbra.