The Hindu : National : Total lunar eclipse

Online edition of India's National Newspaper
Sunday, May 02, 2004

National

National

Total lunar eclipse

By Lalithasai

CHENNAI, MAY 1. The moon will be an interesting object to watch when it slides into the cone of the shadow of the Earth cast by the Sun during a total lunar eclipse in the early hours of May 5.

The celestial show, which will be visible throughout India starts around 00.18 hours and will last till 3.42 a.m., says P. Iyamperumal, Executive Director of Tamil Nadu Science & Technology Centre.

The beginning of the eclipse will be visible in Asia except extreme northeast. The ending of the eclipse is visible in Africa, Europe, Western Asia, Western Australia, Antarctica, South America except in northwestern part, the eastern North Atlantic ocean, the south Atlantic ocean, the Indian ocean and the extreme southeastern south Pacific ocean.

During this 3-hour-24 minute eclipse, the moon will go deep within the southern part of the Earth's shadow, known as `umbra'. However, during the one-hour-16 minute total eclipse, the moon will not turn totally invisible. A certain amount of sunlight bent by the Earth's atmosphere will still reach the moon.

The moon's disk can take on dramatic hues — from a bright orange, through deep red, dark brown or even dark grey as it's brilliance ranges from bright to dark to nearly invisible.

"Blue wavelengths are scattered away by our atmosphere and they do not reach the moon, but the longer reddish wavelengths do. This causes the moon to be lit up by a reddish orange light, typically giving it a coppery glow during the total lunar eclipse," says the director.

Although the moon is cut off from all direct sunlight while it is in Earth's umbral shadow, the Moon receives indirect sunlight which gets refracted through and modified by Earth's atmosphere.

Another reason for the reddish hue is that the Earth's atmosphere contains varying

amounts of water (clouds, mist, precipitation) and solid particles (dust, organic debris, volcanic ash). This material filters and attenuates the sunlight before being refracted into the umbra.

During the initial and final period of the eclipse, the moon will be in the light outer fringe of the Earth's shadow, known as penumbra. But observers will not be able to find any noticeable difference in the brightness at this stage. The penumbral eclipse beginning at 11-21 p.m on May 4 and ending at 4.40 a.m the next day, will not be visible.

Lunar eclipses only take place during full moon day. But an eclipse does not occur on all full moon days, because the Moon's orbit around the Earth is actually tipped about 5 degrees to Earth's orbit around the Sun. This means that the Moon spends most of the time either above or below the plane of Earth's orbit.

The moon, usually passes above or below Earth's shadows and misses them entirely on a full moon day and so no eclipse takes place. But twice or four times each year, the Moon passes through some portion of the Earth's penumbral or umbral shadows causing an eclipse.

Mr. Iyamperumal says that "Unlike solar eclipses, lunar eclipses are completely safe to watch with naked eyes. Binoculars, will help magnify the view and will make the red coloration brighter and easier to see. We can also make useful observations such as studying the craters on the moon during total lunar eclipses."

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