What is Lunar Eclipse ?

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Lunar eclipses occur when Earth's shadow blocks the sun's light, which otherwise reflects off the moon. There are three types — total, partial and penumbral — with the most dramatic being a total lunar eclipse, in which Earth's shadow completely covers the moon.

The next lunar eclipse will be a total lunar eclipse on Jan. 20-21, 2019 and will be visible from North and South America, Europe and Africa.

Throughout history, eclipses have inspired awe and even fear, especially when total lunar eclipses turned the moon blood-red, an effect that terrified people who had no understanding of what causes an eclipse and therefore blamed the events on this god or that.

Below, you'll find the science and history of lunar eclipses, learn how they work, and see a list of the next ones on tap. [See also our guide to Solar Eclipses.]

When is the next lunar eclipse?

The last lunar eclipse was on July 27, 2018. It was a total lunar eclipse. Here is a schedule of upcoming lunar eclipses:

Jan. 19, 2019: Total eclipse. Visible from North and South America, Europe and Africa.

July 16, 2019: Partial eclipse. Visible from South America, Europe, Africa, Asia and Australia.

Jan. 10, 2020: Penumbral eclipse. Visible from parts of North America, Europe, Africa, Asia and Australia.

June 5, 2020: Penumbral eclipse. Visible from parts of South America, Europe, Africa, most of Asia and Australia.

July 5, 2020: Penumbral eclipse. Visible from most of North America, South America, western Europe and Africa.

Nov. 30, 2020: Penumbral eclipse. Visible from North America, South America, northern Europe, eastern Asia and Australia.

These eclipses are actually remarkably simple considering how interesting and dynamic they can be. Basically, the Earth's shadow blocks most of the sunlight from directly illuminating all -- or a portion -- of the moon's surface.

The umbra is the dark, center shadow, and the outer, more diffused one is known as the penumbra. The penumbra encases the umbra.

NASA keeps a list predicting lunar eclipses until 2100. They also keep data about past lunar eclipses. During the 21st century, Earth will experience a total of 228 lunar eclipses, according to the space agency.

lunar eclipses don't occur during every full moon because of two factors. The first has to do with the variations in the orbital planes between the sun, Earth and the moon.

A lunar eclipse can occur only at full moon. A total lunar eclipse can happen only when the sun, Earth and moon are perfectly lined up — anything less than perfection creates a partial lunar eclipse or no eclipse at all.

Some understanding of simple celestial mechanics explains how lunar eclipses work. [Infographic: Total Eclipse of the Moon]

The rotational layout of the sun and Earth forms an ecliptic plane between the two celestial bodies. The moon, however, doesn't circle the Earth in line with this same plane -- instead, its orbit is about 5 degrees off kilter.

Types of lunar eclipses

Total lunar eclipse: Earth's full (umbral) shadow falls on the moon. The moon won't completely disappear, but it will be cast in an eerie darkness that makes it easy to miss if you were not looking for the eclipse.

Some sunlight passing through Earth's atmosphere is scattered and refracted, or bent, and refocused on the moon, giving it a dim glow even during totality.

occurrence of a lunar eclipse also depends on whether the moon is in the full moon phase when it reaches a node. So the second factor to note is that as the moon orbits the Earth, it doesn't complete its full cycle from new moon to new moon as quickly as it returns to the ecliptic plane, creating a disparity between the two occurrences.

If you were standing on the moon, looking back at the sun, you'd see the black disk of Earth blocking the entire sun, but you'd also see a ring of reflected light glowing around the edges of Earth — that's the light that falls on the moon during a total lunar eclipse.

Partial lunar eclipse: Some eclipses are only partial. But even a total lunar eclipse goes through a partial phase on either side of totality.

Penumbral lunar eclipses are difficult to see and occur when the moon grazes or passes through the penumbral shadow only. A partial lunar eclipse occurs when a portion of the moon is obscured by the umbra. The moon fully enters the umbral shadow during a total lunar eclipse.