When the moon passes directly behind Earth into its shadow, which is also known as umbra, it causes lunar eclipse. This event can only happen when the Sun, the moon and our Earth are exactly aligned with Earth positioned in the middle. Thus, a lunar eclipse can only be viewed on the night of a full moon.
Solar Eclipse vs Lunar Eclipse
Many people often get confused between a solar and a lunar eclipse. Both these events involve interactions between the Sun, Earth and the moon. But the interactions between them are very different for both eclipses.
Usually, a solar eclipse can only be observed from a certain comparatively small area of the world. But a lunar eclipse can be viewed from anywhere in the nightside of Earth. A total solar eclipse only lasts for a few minutes at any given place in our Earth because of the smaller size of the shadow of the moon, but a lunar eclipse can be observed for a few hours.
READ ALSO : What causes a Solar Eclipse?
How many types of Lunar Eclipse exist?
When the moon passes through Earth’s penumbra, the lighter region of the shadow, it causes penumbral lunar eclipse . A subtle darkening of the surface of the moon is caused by the penumbra. Total penumbral eclipse is a special type of penumbral lunar eclipse.
During this eclipse, the moon lies only within Earth’s penumbra. Total penumbral eclipses are a very rare event. When this type of eclipse happens, the portion of the moon which is closest to the umbra, the darkest region of the shadow, can appear slightly darker than the rest part of the moon.
When only a portion of the moon lies in the region of umbra, it causes partial lunar eclipse.
A total lunar eclipse can be viewed only when the moon travels completely into Earth’s umbra. This type of eclipse can last up to approximately 107 minutes.
But the total time between the moon’s first and last contact with the shadow of our Earth is much longer. This time span could last up to almost four hours.
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What is a Selenelion?
A selenelion or selenehelion, which is also known as horizontal eclipse, occurs when both the Sun and an eclipsed moon can be observed at the same time. This rare event can only be observed either before sunset or after sunrise.
Both these bodies- the Sun and the eclipsed moon will appear just above the horizon in the sky at almost opposite points. For this type of arrangement of these bodies, the phenomenon is termed as a horizontal eclipse. Even though the moon is in Earth’s umbra, we can see both the Sun and eclipsed moon at the same time during horizontal eclipse.
This happens because of the refraction of light through the atmosphere of our Earth. It causes each of the moon and the Sun to appear slightly higher than their actual geometric position in the sky.
READ ALSO : How hot is the Surface of the Sun?
Timing of Lunar Eclipse
The timing of a lunar eclipse is decided by its contacts-
First Contact- It is the beginning of the penumbral eclipse when Earth’s penumbra just touches outer limb of the moon.
Second Contact– It is the beginning of the partial eclipse when Earth’s umbra just touches the outer limb of the moon.
Third Contact– This is the beginning of the total eclipse when the moon’s surface is completely within Earth’s umbra.
Greatest Eclipse– It is the peak stage of the total eclipse when the moon is at closest to the centre of Earth’s umbra.
Fourth Contact– It is the end of the total lunar eclipse when the outer limb of the moon just starts to exit from the Earth’s umbra.
Fifth Contact– This is the end of the partial eclipse. At this point, Earth’s umbra leaves the moon’s surface.
Sixth Contact– It is the end of the penumbral eclipse when Earth’s penumbra is no longer making any contact with the moon.
In ancient times, various civilizations used the monthly cycle of moon to calculate the passage of time. Some calendars are actually synchronized to the phases of the Moon, which are known as lunar calendars. Some examples of the lunar calendars are- the Hebrew, Muslim and Chinese calendars.
READ ALSO : What is the temperature of the Moon’s surface?
What causes a Blood Moon?
A totally eclipsed moon is sometimes termed as a “blood moon” because of its reddish colour. One of the most popularly known blood moons was observed on 8th October, 2014. It was visible across the major part of the Americas and Asia.