lunar eclipse

The following text has been blatantly swiped from John Flannerys article on www.science.ie

Feel free to post any observations/photos here or to the irishastronom.org site.

Cheers,
~Al
--
Irish Light Pollution Awareness Campaign
www.irishastronomy.org/ilpac


A total eclipse of the Moon for National Science Week
8 November 2003 - 8 November 2003

A quick glance skyward close to midnight of Saturday, 8th November 2003 may reveal that all is not well with lovely Luna. Darkness creeps across her face as she immerses herself in the cone of the Earth’s shadow splayed into space and undergoes a prescient total lunar eclipse to open the celebrations of National Science Week for 2003. This is the second total lunar eclipse of 2003 (May’s was clouded out!)

Tales of fear and dread - Lunar eclipses, while no longer of any major scientific importance, have a special appeal for even the most casual sky watcher among us. As the Earth's shadow glides across the moon's face, our senses are heightened to the effects. The blaze of stars bursting forth as the sky darkens, no longer awash with the glare of the Full Moon. The subtle colourings of the lunar disk — maybe the edge of the Earth's shadow tinged with rainbow like hues caused by clouds at the Earth's limb breaking up sunlight into a kaleidoscope of colour. No longer are we in fear of what robs the moon of its light.

The blood red colour of the lunar disk during an eclipse is what probably gave rise to early beliefs that it was being attacked by an invisible creature. To this end, it was thought that creating a chorus of noise would frighten the creature away. The Chinese idea that a dragon was responsible was a widespread theme. People took to banging pots and pans in an effort to scare off the beast.

Other interpretations of eclipses were common. In Tonga, clouds alone were believed to cause an eclipse while the tribes of the Kalahari thought that the moon had suffered an illness. Some peoples of the Middle East believed that the moon showed its displeasure with events on Earth by temporarily turning its face away from us while others thought the moon painted her face to hide from some celestial danger.

Columbus and the eclipse - Eclipses have influenced numerous events in world history. Probably one of the more famous instances of someone using their knowledge of a lunar eclipse to help them in a tricky situation occurred when Christopher Columbus was on his fourth voyage to the New World.

The great seafarer was in desperate straits in the autumn of 1503. His tiny fleet was unseaworthy due to shipworm and after abandoning two of his vessels he beached the others on the island of Jamaica. After six months as castaways, half the crew mutinied, engaged in pitched battles with those loyal to Columbus and robbed and murdered the natives of the island. Lack of trade worthy goods and the depredations of the mutineers caused the Jamaicans to stop supplying Columbus and his crew with food.

It was during this dire situation that a moment of inspiration came to Columbus. While thumbing through his nautical almanac he noticed that a total lunar eclipse was due to fall on the 29th of February 1504. Three days before the eclipse was due he told the native chiefs that the Christian god was angry with the populace for not helping the visitors to their shores and would give a clear sign in the heavens. On the appointed evening, the Moon duly became “inflamed with wrath” and the native chiefs implored Columbus to restore the Moon’s light. Following his “success”, the islanders kept Columbus and his crew supplied with food until a relief ship arrived.

What is a lunar eclipse? A total lunar eclipse occurs when the Moon passes through the shadow of the Earth cast into space. This means that we can only get a lunar eclipse during time of Full Moon when the Sun, Earth and Moon are in a straight line.

We don’t get a solar or lunar eclipse every month however because the orbit of the Moon about the Earth is tilted with respect to the Earth’s equator. During a total lunar eclipse our atmosphere acts like a lens bending sunlight around the Earth’s limb onto the Moon. Longer wavelengths of light (red and orange) penetrate our atmosphere better than shorter (blue) so during totality the Moon takes on a reddish-orange hue.

The effect is similar to the reddening of the setting Sun. It once led someone to comment that the red colour of the eclipsed Moon is due to all the sunrises and sunsets around the world being painted on the Moon — a rather nice and perceptive observation.

Eclipse phenomena - Normally the glare of the Full Moon floods the sky and washes out all but the brighter stars. During totality however, many fainter stellar pinpoints burst into view when the light of the lunar disk is dimmed.

Very little dimming is noticed during the initial stages of a lunar eclipse as the Moon slides through the penumbral, or outer, portion of the Earth’s shadow. Thereafter, you will begin to see a slight darkening at the leading limb as the Moon slips deeper into eclipse. This is when we anticipate the dramatic play of effects on the lunar disk.

If the Moon passes well north or south of the centre of the Earth’s shadow then the contrast between both hemispheres can be quite marked with the tones graded from bright to dark across the disk.

The Danjon scale - Atmospheric conditions at the Earth’s limb can often have an effect on the visibility of the Moon during an eclipse. The brightness of lunar eclipses can be rated according to a scale devised by the French astronomer Antoine Danjon in the early twentieth century. It is graded as follows:

L = 0: Very dark eclipse; Moon hardly visible, especially near mid-totality.

L = 1: Dark eclipse; grey-to-brown colouring; details on the disk hardly visible

L = 2: Dark red or rust coloured eclipse with dark areas in the shadow centre, the edge brighter

L = 3: Brick red eclipse, the shadow often bordered with a yellow edge

L = 4: Orange or copper-coloured, very bright eclipse with bluish edge

If anyone would like to do a little science then the Danjon scale is a very useful measurement of eclipse brightness. The key is to carry out your estimation on the scale as close to mid-eclipse as possible. Make a note too whether each lunar hemisphere deserves a Danjon scale grading of its own.

Dust and ash ejected into the atmosphere from the eruption of Mt. Pinatubo in the Philippines during 1991 led to dark eclipses in the following years. The lunar eclipse of December 1992 which was visible from Ireland was rated as L=0.5 by many observers.

The lunar eclipse on the night of November 8th

Penumbral eclipse begins 22:15:00 Partial eclipse begins 23:32:21

Totality begins 01:06:07

Totality ends 01:30:38

Partial eclipse ends 03:04:24

Penumbral eclipse ends 04:21:48

The table here highlights the sequence of events during the evening. Very little dimming of the lunar disk will be noticed before 11pm but thereafter, you will begin to see a slight darkening on the left limb of the Moon as the shadow slowly creeps across the Moon’s face. Totality is in the early hours of November 9th. The Moon barely dips into the southern part of the Earth’s umbral shadow as totality lasts a relatively brief 25 minutes. Expect the lunar disk to have a bright rim along its southern edge.

For the record, two total lunar eclipses are also visible from here on May 4th and October 28th, 2004. More on eclipses from Fred Espenak’s website — http://sunearth.gsfc.nasa.gov/eclipse/eclipse.html


Location:
midnight Saturday, 8th November 2003

Organisers:
John Flannery, South Dublin Astronomical Society (skynotes@eircom.net)