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Types of Lunar Eclipses
There are three types of lunar eclipses: penumbral lunar eclipse, partial lunar eclipse and total lunar eclipse. The type of eclipse and its duration depends on the location of the moon on its orbital node. A penumbral eclipse occurs when the moon passes through the penumbral shadow of the Earth. Penumbra refers to the boundary areas of the shadow; the area in full shadow is called umbra. A partial lunar eclipse happens when a part of the moon passes through Earth's umbral shadow. In a total lunar eclipse, the entire moon passes through Earth's umbral shadow.
Duration &Frequency of Lunar Eclipse
Depending on the location of the moon in the orbital node, the duration and length of the eclipse also changes. The duration of a lunar eclipse can vary from 1 hour and 30 minutes to 3 hours and 40 minutes. If a penumbral lunar eclipse is also counted, two to five lunar eclipses can occur per year. Penumbral lunar eclipses are not visible to the naked eye. Two to three umbral lunar eclipses happen every year and are visible somewhere on the Earth.
Location of Moon
The plane of the moon's orbit is inclined about 5 degrees to the plane of the Earth's orbit. Only when the moon, Earth and sun align in the same orbital plane can a lunar eclipse occur. Also, the Earth must be in between the moon and sun.
Phases of the Moon
The phase of the moon depends of the position of the moon to Earth and the sun. The moon has eight main phases. During a lunar eclipse, the phase of the moon is full moon. The other phases are new moon, waxing crescent moon, quarter moon, waxing gibbous moon, waning gibbous moon, last quarter moon and waning crescent moon. The moon reaches half way through its revolution two weeks after the new moon. Thus it coincides with the Earth, and we can see a full moon. At this time, if the moon aligns exactly with the Earth and sun, a lunar eclipse occurs. Even though we have 12 full moons, we do not have 12 lunar eclipses every year.