By : Prabhavati Akashi : The solar eclipse on Wednesday, July 22, 2009 is the longest total solar eclipse of the
twenty-first century and will not be surpassed in duration until June 13, 2132. Its totality will last for up to 6 minutes and 44 seconds and will be visible in India, some of the Japanese islands, China and Pacific Ocean.
The eclipse begins with the sunrise in the western part of India, travels to eastern part of
India, crosses to Mynamar (Burma), small islands of Japan and China. Considering the Earth as a
whole, the eclipse begins at 5:28 am IST when the shadow of the Moon touches the Earth at local
sunrise at a point in the Arabian Sea close to the western coast of India. The eclipse ends at 10:42 am IST when Moon’s shadow finally leaves the Earth at local sunset at a point in the South Pacific Ocean.
View in India
In India Surat, Indore, Bhopal, Jabalpur, Varanasi and Patna are some of the cities lie close to the central part of the totality. According to a research by National Aeronautics and Space Administration (NASA), Taregana, a place near Patna, is the best location as the altitude of the sun will be about 15 degrees here at the time of total eclipse.
Following is the Map of India showing variation in the magnitude of eclipse in different regions. Area encompassed between lines of 1.0 magnitude will experience total eclipse of the Sun. Decreasing magnitude lines indicate proportionately partial eclipse.
This is second in the series of three eclipses in a month. There was a lunar eclipse on July 7 and now a solar eclipse on July 22 and then a lunar eclipse on August 6.
How does it occur?
A solar eclipse occurs when the moon passes between the Sun and the Earth so that the Sun is fully or partially covered. Without the sun’s light, the sky darkens enough for stars to be seen and the corona makes a spectacular halo around the moon. It can only occur at New Moon when the Moon passes between Earth and Sun. If the Moon’s shadow happens to fall upon Earth’s surface at that time, one sees some portion of the Sun’s disk covered or ‘eclipsed’ by the Moon.
Since New Moon occurs every 29 and 1/2 days, why can’t we have a solar eclipse once every month? It is because the Moon’s orbit around Earth is tilted 5 degrees to Earth’s orbit around the Sun. As a result, the Moon’s shadow usually misses Earth as it passes above or below our planet at New Moon. At least twice a year, the geometry lines up just right so that some part of the Moon’s shadow falls on Earth’s surface and an eclipse of the Sun is seen from that region. The
Moon’s shadow actually has two parts:
1. Penumbra : The Moon’s faint outer shadow. Partial solar eclipses are visible from within the penumbral shadow.
2. Umbra : The Moon’s dark inner shadow. Total solar eclipses are visible from within the umbral shadow.
Following is the geometry of the total solar eclipse:
Is it safe to watch with naked eyes?
Partial eclipses, annular eclipses, and the partial phases of total eclipses are never safe to watch without taking special precautions. Even when 99% of the Sun’s surface is obscured during the partial phases of a total eclipse, the remaining photospheric crescent is intensely bright and cannot be viewed safely without eye protection. The Sun can be viewed safely with the naked eye only during the few brief seconds or minutes of a total solar eclipse.
The safest and most inexpensive of these methods is by projection, in which a pinhole or small opening is used to cast the image of the Sun on a screen placed a half-meter or more beyond the opening. Projected images of the Sun may even be seen on the ground in the small openings created by interlacing fingers, or in the dappled sunlight beneath a leafy tree. Binoculars can also be used to project a magnified image of the Sun on a white card, but you must avoid the
temptation of using these instruments for direct viewing.
The Sun can be viewed directly only when using filters specifically designed for this purpose. Such filters usually have a thin layer of aluminum, chromium or silver deposited on their surfaces that attenuates ultraviolet, visible, and infrared energy. No filter is safe to use with any optical device (i.e. – telescope, binoculars, etc.) unless it has been specifically designed for that
purpose. Experienced amateur and professional astronomers may also use one or two layers of completely exposed and fully developed black-and-white film, provided the film contains a silver emulsion. Since all developed color films lack silver, they are always unsafe for use in solar viewing.
Do not experiment with other filters unless you are certain that they are safe. Consult your local planetarium or amateur astronomy club for additional information. Happy safe-viewing!