More About Lunar Eclipses

Firstly let me describe a few key terms, the shadow of the Earth can be divided into two distinctive parts: the Umbra and Penumbra. The Umbra (Latin for "shadow") is the innermost and darkest part of a shadow, where the light source is completely blocked by the occluding body (Earth). The Penumbra (from the Latin paene "almost, nearly" and umbra "shadow") is the region in which only a portion of the light source is obscured by the occluding body. A total lunar eclipse occurs when the Moon passes directly behind the Earth into its Umbra, the type and length of an eclipse depends upon the Moon's location relative to its orbital nodes.

 

 

 

 

 

 

Types of Lunar Eclipses:

1) A Penumbral Eclipse occurs when the Moon passes through the Earth's penumbra. The Penumbra causes a subtle darkening of the Moon's surface. A special type of Penumbral eclipse is a total Penumbral eclipse, during which the Moon lies exclusively within the Earth's penumbra. Total Penumbral eclipses are rare, and when these occur, that portion of the Moon which is closest to the Umbra can appear somewhat darker than the rest of the Moon.

 

2) A Partial Lunar Eclipse occurs when only a portion of the Moon enters the Umbra.

 

3) 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. Nevertheless, the total time between the Moon's first and last contact with the shadow is much longer, and could last up to 6 hours. The relative distance of the Moon from the Earth at the time of an eclipse can affect the eclipse's duration. In particular, when the Moon is near its apogee, the farthest point from the Earth in its orbit, its orbital speed is the slowest. The diameter of the Umbra does not decrease appreciably within the changes in the orbital distance of the Moon. Thus, a totally eclipsed Moon occurring near apogee will lengthen the duration of totality.

 

The timing of total lunar eclipses are determined by its contacts:

P1 (First contact): Beginning of the Penumbral eclipse. The Earth's penumbra touches the Moon's outer limb.

U1 (Second contact): Beginning of the partial eclipse. The Earth's umbra touches the Moon's outer limb.

U2 (Third contact): Beginning of the total eclipse. The Moon's surface is entirely within the Earth's umbra.

Greatest eclipse: The peak stage of the total eclipse. The Moon is at its closest to the center of the Earth's umbra.

U3 (Fourth contact): End of the total eclipse. The Moon's outer limb exits the Earth's umbra.

U4 (Fifth contact): End of the partial eclipse. The Earth's umbra leaves the Moon's surface.

P4 (Sixth contact): End of the Penumbral eclipse. The Earth's penumbra no longer makes contact with the Moon.

 

Lastly you may be wondering why during totality the shadow on the Moon's face changes, instead of of the dark shadow it appears red ... why? The answer is Earth's atmosphere, the Earth's atmosphere extends about 80 kilometers (50 miles) above the Earth's surface, during a total lunar eclipse when the moon is submerged in Earth’s shadow there is circular ring around Earth (the ring of our atmosphere) through which the sun’s rays pass. Sunlight is composed of a spectrum of light with a range of frequencies/wavelengths, as sunlight passes through our atmosphere the green to violet portion of the light spectrum is essentially filtered out. This same effect is what makes our sky blue during the day. Meanwhile the reddish portion of the spectrum is least affected, when this reddish light first entered the atmosphere it was bent (refracted) toward the Earth’s surface, it’s bent again when it exits on the other side of Earth. This double bending sends the reddish light onto the moon during a total lunar eclipse. Depending on the conditions of our atmosphere at the time of the eclipse (dust, humidity, temperature and so on can all make a difference), the surviving light will illuminate the moon with a color that ranges from copper-colored to deep red. In December 1992, not long after the eruption of Mount Pinatubo in the Philippines, there was so much dust in Earth’s atmosphere that the totally eclipsed moon could barely be seen.

 

On April 15, 2014 the time between the Moon entering and exiting the Earth's Penumbra was 5 hours and 44 minutes (when an observable shadow first/last appears over the Moon). The period of total eclipse (the Moon fully within the Earth's Umbra during which it appears in that distinctive copper-red colour) lasted 1 hour and 18 minutes.

 

This is the first of 2 lunar eclipses of 2014, the second being on October 8, 2014.

 

 

 

 

 

 

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