Tuesday, December 6, 2011

Look out for the Total Lunar Eclipse of 10 Dec 2011 – You can't miss this!


All avid eclipse watchers would be waiting for a great opportunity to see a total eclipse of the Moon early on the night of Saturday, 10 December this year, just 4 days away. The last such eclipse occurred only six months ago, on June 15-16, and was a major disappointment in most places because of cloudy skies most of the time, compounded by the late hour of the event which also discouraged most people.  However, the next one should be quite different for it is scheduled at a time of the year when clear skies are almost a certainty, with the eclipse beginning soon after sunset that day.

Some of my earlier blog posts relate to eclipses in general and solar eclipses in particular. My last two posts in June relate specifically to the total lunar eclipse of June 15-16 and I urge the reader to go through both of them to set the stage for the forthcoming one.

As pointed out in my earlier posts, solar and lunar eclipses as seen from the Earth would not have been possible at all but for a very fortuitous and remarkable circumstance relating to the three celestial bodies. The apparent sizes of the Sun and the Moon as seen by us on Earth just happen to be nearly the same, approximately half a degree in angular diameter. When the Earth comes between the Sun and the Moon as on a full moon day, the latter can be found in the shadow of the Earth and hence sunlight will not be falling on it directly.  This is when a lunar eclipse occurs.  As seen from any point on the Earth, the eclipse may be partial or total.  One might expect the Moon to be completely hidden from view during a total lunar eclipse.  However, the whole of the Moon can be seen clearly as a faint coppery red object because of sunlight scattered by the Earth’s atmosphere, predominantly in the red, falling on the lunar surface and thereby illuminating it.  It is a wonderfully beautiful sight to behold! Would it be fair to regard the Moon as truly eclipsed?

I am reproducing the following diagram from the earlier post to show the geometry of the three stellar objects during the lunar eclipse.

Forthcoming Eclipse of the Moon

The forthcoming total lunar eclipse of December 10 will occur when the Moon is situated in the northern constellation Taurus, bordering the constellations Orion and Auriga, as shown in the following chart generated with the Starry Night Pro Plus 6 astronomy software package.  The night sky is rich in several prominent constellations, particularly Orion, and some of the brightest stars can also be seen in the neighborhood.  These include Sirius, Betelgeuse, Rigel, Aldebaran and Capella.  During the period of totality that lasts about 51 minutes, the night sky in that region should be spectacular, especially if the viewer is located well away from disturbing lights.  Not far from the eclipsed Moon is the beautiful star cluster Pleiades, a great sight even for the naked eye. One can also look for the famous Orion Nebula (M43) amidst the row of stars seen in the 'hunter's dagger' within the Orion Constellation.  It is a particularly good sight with binoculars, as is the Pleiades cluster.
After sunset, planet Venus in the western sky and planet Jupiter near the zenith, not seen in the chart below, are two of the brightest objects in the night sky that can scarcely go unnoticed.

[Click to enlarge]

The Moon's contact times with the Earth's umbral and penumbral shadows are shown in the following figure adapted from the NASA/Espenak eclipse website.  The times shown are in Universal Time (UT).  Add 5:30 to obtain the local time (IST) anywhere in India.  Thus, the onset of totality will start at approximately 7:36 PM on the evening of December 10 and end a little after 8:27 PM.  Of course the partial phase will have set in much earlier – at around 6:15 PM, a little after sunset in a place like Mysore.

Eclipse Visibility

The following illustration, also from the NASA/Espenak website, shows the visibility of the eclipse from any place on the Earth.  As is evident, the event can be seen in its totality from most parts of Asia and Australasia as well as many other regions. 

Watching the Eclipse

In most parts of India, sunset on 10th evening should be greeted by a bright and brilliant full Moon rising in the east.  The path of the Moon will have already entered the penumbral shadow around 5:03 PM.  For some time at least after darkness, it may be extremely difficult to notice even a slight decrease in the brightness of the Moon.  Only skilled observers may detect a faint shading across the lunar disk. This phase will last about an hour, until the Moon starts entering the umbral shadow of the Earth around 6:15 PM.  This marks the beginning of the partial phase of the eclipse.  Thereafter one should be able to see a progressive 'eating away' of the Moon's surface and a marked decline in brightness as the visible portion of the lunar surface reduces. 

As usual, the rising full Moon will appear much bigger than normal because of illusion associated with our vision of celestial objects near the horizon.  In some regions like western United Sates, one can expect to see the fully eclipsed Moon at sunset appearing not only beautifully reddish, but also inflated because of such illusion.

Around 7:36 PM, totality will set in when the whole of the lunar surface is inside the Earth's umbral shadow.  However, as already explained, the Moon continues to be visible as a faint copper red disk.  This phase lasts the next 51 minutes, with small but noticeable variations in the overall brightness.  This is the time when the viewer can soak in a wonderful view of the night sky with a faint reddish full Moon appearing to be suspended like a friendly ghost in the sky with rich star fields nearby.  A pair of binoculars would be a great visual aid to use at this juncture.

The total phase will end by 8:27 PM when the Moon should begin to shine in direct sunlight.  It should progressively grow brighter and restored very nearly to its full glory when the partial phase ends around 9:37 PM.  However, the Moon will remain in the penumbral shadow until around 11.00 PM.  This marks the end of what should be another memorable total lunar eclipse so soon after the last one.

Unlike a solar eclipse where one has to take special precautions and safe filters to view the event, the Moon is a totally harmless object at any time, and especially so during an eclipse, no matter what the media may project.  The astrologers and soothsayers will no doubt have their usual field day with a highly gullible public willing to believe anything portentous and sensational and not caring for a scientific perspective of the event.


Lunar eclipse photography is easy, particularly with high zoom digital SLR cameras, and requires no special equipment or filters. However, a sturdy tripod is a must, especially during the total phase.  Since the whole event lasts quite a long time, photographs can be taken in a well planned manner at regular intervals of time.  One may have to experiment with the exposure times because of the changing brightness of the sunlit part of the lunar surface as the eclipse progresses. It is best to set the aperture at maximum so that the exposure times can be minimized. 

With a zoom camera, the longest zoom setting will naturally give a much larger image than otherwise and should therefore be invariably preferred. With an ordinary (wide field) camera it would be interesting to capture the Moon in its natural setting, against the backdrop of interesting scenery in the foreground.  An interesting way to present the wide field pictures taken at regular intervals of time is to make a composite image for which a photo editing software package may come in handy.


Unlike the last lunar eclipse, this one should be easily observable by the vast majority of people in the country and elsewhere if they choose to do so.   There should be no cause for any excuses. If you miss this, you will have to wait until October 8, 2014 for the next total lunar eclipse visible from Asia.  Remember, partial lunar (and even solar) eclipses are far from being as exciting as total ones, though more frequent.

This time I am planning to go with Chiranjeevi and others to a remote location, well away from disturbing lights, and do a better job than last time, combining photography with visual observations. I would love to hear from viewers by way of observations and comments posted here or mailed to me directly.  I will try to correlate these with my own experiences and report in a later post very soon.

[PS: At the time of uploading this post, the weather outlook in the southern part of Karnataka state, including the Mysore-Bangalore region, is not entirely encouraging, but the probability of clear skies after sunset is very high.  Even at its worst, the situation should be a great deal better than last time.]


A V G Rao said...

Thanks for the info.

glasglary said...

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Anonymous said...

Madamme Curie should not be wearing a digital watch.

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