What is Lunar Eclipse ?

During the partial phase, the sun, Earth and moon are not quite perfectly aligned, and Earth's shadow appears to take a bite out of the moon.

The time the moon spends encased in the umbra is called totality. If you hear someone referring to the length of totality of a lunar eclipse, they're talking about the middle phase of the overall event.

Penumbral lunar eclipse: This is the least interesting type of eclipse, because the moon is in Earth's faint outer (penumbral) shadow. Unless you're a seasoned skywatcher, you likely won't notice the effect, in which the moon is subtly shaded by Earth's shadow.

Totality doesn't include the time on either side of the umbra when the moon was passing through the penumbral or partial eclipse phases. The length of totality can range from around 20 to 100 minutes.

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.

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:

The blood-red moon

The moon may turn red or coppery colored during the total portion of an eclipse. The red moon is possible because while the moon is in total shadow, some light from the sun passes through Earth's atmosphere and is bent toward the moon.

There are many dynamic interactions going on when the shadowy Earth eclipses her celestial companion. The color and brightness of the moon during a lunar eclipse varies according to this planet's atmospheric conditions.

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.

Eclipses with this level of luminosity are typically very dark. The moon will be difficult to identify against the sky. Earth's atmosphere is dense with particles at this end of the scale.

While other colors in the spectrum are blocked and scattered by Earth's atmosphere, red light tends to make it through easier. The effect is to cast all the planet's sunrises and sunsets on 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]

These eclipses are also dark, but the moon may appear with dark brown or dark gray hues. Identifying lunar features is challenging.

The moon will appear a deep red or rusty shade. The central umbra is dark, but may appear lighter around the edges.

Because the moon's orbit around Earth lies in a slightly different plane than Earth's orbit around the sun, perfect alignment for an eclipse doesn't occur at every full moon. A total lunar eclipse develops over time, typically a couple hours for the whole event. Here's how it works: Earth casts two shadows that fall on the moon during a lunar eclipse: The umbra is a full, dark shadow. The penumbra is a partial outer shadow. The moon passes through these shadows in stages. The initial and final stages — when the moon is in the penumbral shadow — are not so noticeable, so the best part of an eclipse is during the middle of the event, when the moon is in the umbral shadow.

This luminosity is characterized by a brick-red moon, with definite, possibly yellowish brightening around the edges of the umbra.

Eclipses at this end of the scale appear a bright copper-red or orange color. The rim of the umbra is very bright with a bluish tint. These eclipses are the result of less atmospheric density.

Total eclipses are a freak of cosmic happenstance. Ever since the moon formed, about 4.5 billion years ago, it has been inching away from our planet (by about 1.6 inches, or 4 centimeters per year). The setup right now is perfect: the moon is at the perfect distance for Earth's shadow to cover the moon totally, but just barely. Billions of years from now, that won't be the case.

Lunar eclipses happen infrequently. On average, they occur up to three times a year, if at all (although three in one year is rare). About a third of these occurrences are the faint penumbral 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.

Partial lunar eclipses take place about another third of the time and are worth checking out. The rest of the time, total lunar eclipses are wowing crowds of fascinated spectators and astrophotographers.

Partial lunar eclipse: Some eclipses are only partial. But even a total lunar eclipse goes through a partial phase on either side of totality. During the partial phase, the sun, Earth and moon are not quite perfectly aligned, and Earth's shadow appears to take a bite out of the moon.

You can view a lunar eclipse from anywhere that night has befallen (at varying times throughout the evening), and it appears somewhat uniformly to people throughout a specific region.

The amount of time an eclipse lasts depends on the type of eclipse and what part of the shadow the moon is passing through. The longest lunar eclipses may last a few hours, from start to finish.

Penumbral lunar eclipse: This is the least interesting type of eclipse, because the moon is in Earth's faint outer (penumbral) shadow. Unless you're a seasoned skywatcher, you likely won't notice the effect, in which the moon is subtly shaded by Earth's shadow.