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SOLAR and LUNAR ECLIPSES : Part 2



LUNAR ECLIPSES


Lunar eclipses occur because the monthly orbital path of the Moon can sometimes cause the illuminated lunar disk to disappear behind the projected shadow of the Earth for a short time. They only can happen during the just few minutes or several hours around the time of the Full Moon.

Unlike solar eclipses, lunar eclipses are slightly more common due to the greater apparent size of the Earths shadow as projected directly diametrically away from the Sun. As such, lunar eclipses roughly occur on average once or twice each yearly, with at least one occurring in the same part of the world once every one, two or three years.

Duration of any visible lunar eclipse can last as long as two hours fifty minutes, with the totality lasting about half of this, or about one hour forty minutes.


Three Types of Lunar Eclipses

There are three types of solar eclipses. Namely;

Total, Partial and Penumbral


Components of the observed shadows appear as two distinct parts. These are the umbra and penumbra, and thirdly, the graduated shadow boundary that lies between the umbra and penumbral — the eclipse terminator.

Lunar Eclipses
 
Figure 3.1: < span class="qa">Lunar Eclipses

Figure 3.1 showing the lunar path as it enters and exits the Earths shadow during total lunar eclipses.


1) The umbra is the darkest portion seen during lunar eclipses. When the Moon passes through this shadow, it does not completely disappear from view, as sunlight from the Earths atmosphere refracts through it then is projected onto the surface of the Moon. This gives the Moon some illumination, making the umbral colour is usually as dull brick red to deep red to deep orange, with the depth of colour mostly depending on the slight variable distance between Earth and Moon. This is also related to the lunar distance when immersed within the shadow. As such, the orbital inclination of the Moon does not always travel through the mid-point of the Earth shadow, so we see only a partial lunar eclipse.

2) The penumbra is produced by the secondary shadow of the Earth as projected onto the Moon. The best way to imagine how it is created, is to see it from the lunar perspective. From the Moon, the Sun would appear partially obscured or eclipsed by the round bulk of the Earth, causing the amount of sunlight to be reduced in intensity. We therefore see to slight drop in intensity compared to the brightness of Full Moon. It is usually impossible to see this visually, unless you know about the event beforehand. Penumbral eclipses can only be observed with suitable electronic light-sensitive equipment, and can be measured during the partial lunar eclipse phase, or even just before or after each total lunar eclipse.

3) Dividing between the umbra and penumbra is the thin transitional region that sometimes appears as odd-looking colour bands. Some of these shadow bands maybe seen as grey, but sometimes they appear like the familiar colours of the rainbow, except in the reverse order.

Each lunar eclipse path is seen from by about half the sphere of the Earth. in specific locations, often daylight will intervene, and this may reduce this percentage of the Earth that sees it considerably.

Appearance of the Moon During Lunar Eclipses

Depending where the Moon is in its orbit, determines the eclipse phase observed, and this varies from lunar eclipse to lunar eclipse. Deviation of this intersection path are due to the 5½° inclination of the lunar orbit.

Where the lunar path crosses the projected shadow of the Earth can vary also in angle. This depends on the location of the Moon at the time of the eclipse on the ecliptic. (As in the example of Figure 3.1, the angle shown is the high inclined in the sky.)

When the Moon happens to be at the place where the lunar orbit happens to exactly intersects the ecliptic, the lunar path will cross the centre of the umbral shadow. Such lunar eclipses at mid-eclipse will often appear very dark deep-red, where in city skies can even cause the Moon to almost disappear to the naked-eye.

Any colour seen in deep lunar eclipses are also affected by the distance between Earth and Moon, which will appear darker if the Moon is also near perigee than apogee.)

If the Moon passes above or below the centre of the Earths own shadow, then this will produce either paler red coloured total lunar eclipse or just partial eclipses.

What Would Total Lunar Eclipses Look Like From the Moon?

An observer on the Moon during any total lunar eclipse, would see the jet-black disk of Eath surrounded by a spectacular deep red ring of light. The true cause of the red colour is the atmospheric illumination from the Earth by the refraction of sunlight, with the entire ring being the observation of every sunrise and sunset happening then on Earth. Furthermore, the brightness of this red ring is the same red colour all observers see over the lunar surface. Anywhere away from mid-eclipse, this brilliant ring would instead appear as one slow moving arc as it travels very slowly around the disk of the Earth. Were such a view possible, it would be very inspiring and just as memorable eclipse seen on the Earth!


Table 2.1

Upcoming Lunar Eclipse
2008 - 2015

2008 - 2015
DATE
Eclipse
Eclipse
Type
Duration
hh mm
Geographic Region of Eclipse Visibility
21st Feb 2008 Total 00h 51m Central Pacific, Americas, Europe, Africa
16th Aug 2008 Partial -- South America, Europe, Africa, Asia, Australia
09th Feb 2009 Penumbral -- Eastern Europe, Asia, Australia, Pacific.
07th Jul 2009 Penumbral -- Australia, Pacific, Americas
06th Aug 2009 Penumbral -- Americas, Europe, Africa, West Asia
31st Dec 2009 Partial 01h 02m Europe, Africa, Asia, Australia
26th June 2010 Partial 02h 44m Eastern Asia, Australia, Pacific, West Americas
21st Dec 2010 Total 03h 29m
01h 13mT
Eastern Asia, Australia, Pacific, Americas, Europe
15th June 2011 Total 03h 40m
01h 41mT
South America, Europe, Australia, Africa
10th Dec 2011 Total 03h 33m
00h 51m
Europe, East Africa, Asia, Australia
04th June 2012 Partial 02h 08m Asia, Australia, Pacific, Americas
28th Nov 2012 Penumbral -- Europe, East Africa, Asia, Australia
25th April 2013 Partial 00h 32m Europe, Africa, Asia, Australia
25th May 2013 Penumbral -- Americas, Africa
18th Oct 2013 Penumbral -- Americas, Europe, Africa
15th April 2014 Total 03h 35m
01h 19mT
Australia, Pacific, Americas
08th Oct 2014 Total 03h 20m
01h 00mT
Asia, Australia, Pacific, Americas
04th Apr 2015 Total 03h 30m
00h 12mT
Asia, Australia, Pacific, Americas
28th Sep 2015 Total 03h 21m
01h 13mT
E. Pacific Americas, Europe, Africa
T = Length of Totality

NOTE : The lines coloured light lime green are eclipses visible somewhere in Australia.



Important Disclaimer

The user applying this data for any purpose forgoes any liability against the author. None of the information should be used for either legal or medical purposes. Although the data is accurate as possible some errors might be present. The onus of its use is placed solely with the user.


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Last Update : 26th November 2012

Southern Astronomical Delights © (2012)

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