4 December 2011

Total lunar eclipse set for this weekend

A total eclipse of the Moon will be visible on 10 December 2011, and is the last total lunar eclipse until 2014.
total lunar eclipse

This photo, taken by Jens Hackman of Weikersheim, Germany, during a total lunar eclipse in March 2007, shows the turquoise outskirts and red core of Earth's shadow sweeping across the face of the Moon. Credit: NASA

MARYLAND: A total eclipse of the Moon will be visible on 10 December 2011, and is the last total lunar eclipse until 2014.

The action begins around 11.46pm Australian Eastern Standard Time (12.:46 GMT) when the red shadow of Earth first falls across the lunar disk. By 1:06 am (14:06 GMT), the Moon will be fully engulfed in red light. This event is visible from the Pacific side of North America, across the entire Pacific Ocean to Asia and Eastern Europe. The previous lunar eclipse was on 15 June 2011 and lasted 100 minutes. This eclipse is expected to last for 51 minutes.

“Lunar eclipses are great astronomical events that everyone can enjoy,” said Tanya Hill, astronomer for the Melbourne Planetarium at Scienceworks. “Unlike a solar eclipse, lunar eclipses last for much longer and can be viewed safely from anywhere on the night side of Earth, without the need for protective or special equipment.”

Super-sized total lunar eclipse

Not only will the Moon be beautifully red, it will also be inflated by the Moon illusion for viewers in North America. For reasons not fully understood by astronomers or psychologists, low-hanging Moons look unnaturally large when they beam through trees, buildings and other foreground objects. In fact, a low Moon is no wider than any other Moon, but the human brain insists otherwise.

It might seem puzzling that the Moon turns red when it enters the shadow of the Earth, but in this case, the delicate layer of dusty air surrounding our planet reddens and redirects the light of the Sun, filling the dark behind Earth with a sunset-red glow. The exact hue (anything from bright orange to blood red is possible) depends on the unpredictable state of the atmosphere at the time of the eclipse.

For years, atmospheric scientist Richard Keen of the University of Colorado in the U.S. has studied lunar eclipses as a means of monitoring conditions in Earth’s upper atmosphere, and has become skilled at forecasting these events. “I expect this eclipse to be bright orange, or even copper-coloured, with a possible hint of turquoise at the edge,” he said.

Explaining the colours

Earth’s stratosphere is the key: “During a lunar eclipse, most of the light illuminating the moon passes through the stratosphere where it is reddened by scattering,” he explained. “If the stratosphere is loaded with dust from volcanic eruptions, the eclipse will be dark; a clear stratosphere, on the other hand, produces a brighter eclipse. At the moment, the stratosphere is mostly clear with little input from recent volcanoes.”

That explains the brightness of the eclipse, but what about the “hint of turquoise”? Keen said, “Light passing through the upper stratosphere penetrates the ozone layer, which absorbs red light and actually makes the passing light ray bluer. This can be seen as a soft blue fringe around the red core of Earth’s shadow.”

Look for the turquoise near the beginning of the eclipse when the edge of Earth’s shadow is sweeping across the lunar terrain, he said.

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