Wednesday, November 28, 2012

Penumbral Lunar Eclipse - 28 Nov 2012

There is a Penumbral Lunar Eclipse happening tonight which will be visible in Singapore if the sky is clear.

Date: 28 November 2012, Wednesday
Time: 8:15 pm to - 12:51 am
Greatest Eclipse: 10:33 pm

Moon Rise: East North East (ENE) at 6:47 pm
Moon Set:  West North West (WNW) at 7:47 am (29 Nov)

This eclipse will NOT be visually as spectacular as a Partial or Total Lunar Eclipse. It will only be slightly dimmer during eclipse, i.e. hard to notice if you just take a quick random look at the Moon and didn't know this eclipse is taking place.

This eclipse is also visible in other countries at different local timings:

Image Credit: NASA Eclipse website

There are 3 types of Lunar Eclipse - Penumbral, Partial and Total.

Penumbra is a partial shadow region between a complete shadow (darkest shadow) and a complete illumination. In laymen terms, penumbra is the lighter shadow, umbra is the darker shadow.

Sun, which has a diameter of 109 Earths, shines on Earth. It creates a shadow of Earth beyond the unlit side of Earth. We don't see Earth's shadow at night in the sky because there is usually no nearby object to project this shadow upon - except the Moon.

Due to Moon's tilted orbit around Earth, it usually passes above or below Earth's shadow region. That is why we don't see lunar eclipse every full moon when Sun - Earth - Moon forms a straight line.

This is a good illustration from Wikipedia. But take note the scaling of the size (and distance) of Sun to Earth is distorted for the sake of illustrating the shadow concepts. Remember the Sun can fit in 1,390,000 Earths!

Image Credit: Wikipedia

By proper astronomical definition, a penumbral lunar eclipse is different from a partial lunar eclipse.

For a lunar eclipse to be defined as partial, Moon must pass through a part (no matter how small) of Earth's darker umbra shadow at any time during the eclipse. For Penumbral, only through any part of the lighter shadow. For Total Lunar Eclipse (e.g. 10 Dec 2011 also visible in Singapore), the whole Moon must be inside the darker shadow.

This is a great video illustration of a similar Penumbral Lunar Eclipse captured in Singapore in 2009 by a local amateur astronomer (who joined us at Bishan-Ang Mo Kio Park during the Venus Transit in June 2012):

Some fun things to do for this eclipse tonight:

(1) See if you can visually tell the difference in brightness of the full moon before/after and during the eclipse
(2) Take photos or videos directly or through a telescope to compare the difference. Make sure the camera settings are the kept the same for all the shots (e.g. ISO, exposure, shutter speed).

Take note potential thin clouds or haze rolling on and off in front of the Moon will affect the detection and photographic documentation of this slight drop in brightness.

For more info about Penumbral Eclipse:
(1) NASA Penumbral Lunar Eclipse 2012
(2) Wikipedia


Tonight's Moon position is a good reference point for finding and observing other celestial objects:

Jupiter and the star Aldebaran forms a triangle with Moon. Extending a straight line roughly double the distance from the midpoint of Jupiter-Aldebaran to Moon to the other side of Moon, you will find a tight bunch of stars known as 7 Sisters star clusters (aka Pleiades, Subaru, Messier Object 45).

Full Moon's brightness may drown out the naked-eye detection of 7 Sisters but if the weather is clear enough, should be still spectacular through a pair of binocular or telescope.

Jupiter is approaching its closest distance to Earth on 4 Dec 2012. But visually you cant tell much of difference from now till then. So observe it whenever the skies are clear enough.

Above Aldebaran, notice an inverted V-shape pattern of stars. This represents the inverted horns of Taurus the Bull. Find Aldebaran with your binocular and continue to look slightly above (or around) this star. The gorgeous Hyades star cluster should fill up the binocular view!

Remember to breathe when you see these wonders around the Moon! Good luck and clear skies!

Update 30 Nov 2012:

Check out these awesome Penumbral Lunar Eclipse photos shot in Singapore by Mr Chia and Gavin:

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