Century's longest solar eclipse

The moon has a powerful allure -- it is full of beauty, legend, myth and romance. However the phases of the moon are caused by the relative positions of the earth, sun and moon. The moon goes round the earth in 27.3 days, or 27 days 7 hours 43 minutes, on average.
In astronomical terminology, the new moon is the lunar phase that occurs when the moon, in its orbital motion around the earth, lies between the earth and the sun and is in conjunction with the sun as seen from the earth. The moon then lies in the same direction (longitude) as the sun. At this time, the illuminated half of the moon faces directly towards the sun, and the dark or unilluminated portion faces directly towards the earth, so the moon is invisible as seen from the earth. Full moon occurs as the moon comes into conjunction with the sun when it passes behind the earth.
The first time that the thin waxing crescent is visible after new moon, low in the evening sky just after sunset, marks the beginning of a month in the Islamic calender. This usually happens with moon's age more than 24 hrs. (i.e., from the time of conjunction to the time of evening of observation) and moonset taking place at least about 48 minutes after sunset. When the new moon is in conjunction with the sun as seen from the earth and other conditions satisfy for a solar eclipse to occur in daytime in your city or if there is a solar eclipse anywhere in the world after sunset in your city, then next day is not the first day of lunar month for your city.
A solar eclipse occurs when the Moon passes between the Sun and the Earth so that the Sun is wholly or partially obscured. This can only happen during a new moon, when the Sun and Moon are in conjunction as seen from the Earth. At least two and up to five solar eclipses occur each year on Earth. Total solar eclipses are nevertheless rare at any location because during each eclipse totality exists only along a narrow corridor in the relatively tiny area of the Moon's umbra. A total eclipse occurs when the sun is completely obscured by the Moon. The intensely bright disk of the Sun is replaced by the dark silhouette of the Moon, and the much fainter sun's corona or outer atmosphere is visible. Fig-1
The match between the apparent sizes of the Sun and Moon during a total eclipse is a coincidence. The Sun's distance from the Earth is about 400 times of Moon's distance, and the Sun's diameter is about 400 times the Moon's diameter. Because these ratios are approximately the same, the sizes of the Sun and the Moon as seen from Earth appear to be approximately the same: about 0.5 degree of arc in angular measure.
The Moon's orbit around the Earth is inclined at an angle of just over 5 degrees to the plane of the Earth's orbit around the Sun (the ecliptic). A solar eclipse can occur only when the new moon occurs close to one of the points (known as nodes) where the Moon's orbit crosses the ecliptic. The Moon's orbit intersects with the ecliptic, at the two nodes that are 180 degrees apart. There will always be at least one solar eclipse when the new moon occurs close to the nodes at two periods of the year approximately six months apart.
Spectacular solar eclipses are an extreme rarity within the universe at large. They are seen on Earth because of a fortuitous combination of circumstances that are statistically very improbable. Even on Earth, spectacular eclipses of the type familiar to people today are a temporary (on a geological time scale) phenomenon. Many millions of years in the past, the Moon was too close to the Earth to precisely occult the Sun as it does during eclipses today; and many millions of years in the future, it will be too far away to do so.
The total eclipse only lasts for a few minutes at a given location, as the Moon's umbra moves eastward at over 1700 km/h. Totality can never last more than 7 min 31s, and is usually much shorter; during each millennium there are typically fewer than 10 total solar eclipses exceeding 7 minutes. The last time this happened was June 30, 1973 (7 min 3 sec). Observers aboard a Concorde aircraft were able to stretch the totality to about 74 minutes by flying along the path of the Moon's umbra. The next eclipse exceeding seven minutes in duration will not occur until June 25, 2150. The longest total solar eclipse during the 8,000 year period from 3000 BC to 5000 AD will occur on July 16, 2186, when totality will last 7 min 29 s. For comparison, the longest eclipse of the 21st century will occur on July 22, 2009 and last 6 min 39sec.
In the 21st century, 2001 to 2100 AD, there will be 224 solar eclipses of which 77 will be partial, 72 annular, 68 total and 7 hybrids between total and annular eclipses. The predictions given here are by Fred Espenak of NASA's Goddard Space Flight Center.
An annular eclipse occurs when the Sun and Moon are exactly in line, but the apparent size of the Moon is smaller than that of the Sun. Hence the Sun appears as a very bright ring, or annulus, surrounding the outline of the Moon. Fig: 2
A hybrid eclipse is intermediate between a total and annular eclipse. At some points on the surface of the Earth it is visible as a total eclipse, whereas at others it is annular. Hybrid eclipses are rather rare.
A partial eclipse occurs when the Sun and Moon are not exactly in line, and the Moon only partially obscures the Sun. This phenomenon can usually be seen from a large part of the Earth outside of the track of an annular or total eclipse. However, some eclipses can only be seen as a partial eclipse, because the umbra never intersects the Earth's surface. Fig-3.
In the 21st century, 2001 to 2100 AD, the longest while the longest solar eclipse will be on July 22, 2009, the longest annular eclipse will be on January 15, 2010. The former will be visible from Bangladesh but the later will be visible from Maldives, South Eastern India, Sri Lanka, Myanmar.
Even when a small part of the Earth's surface does come to fall within the umbra and thus experiences a total eclipse, there will be a much larger area surrounding it which is within the penumbra; once again, some of the Sun's light still reaches the Earth and the eclipse is never more than partial outside the path of totality, and even within the path it is still partial Inevitably, then, totality whenever it occurs, is always the climax to an experience which begins and ends with partiality. Fig-4.
When the shrinking visible part of the photosphere becomes very small Baily's beads will occur. These are caused by the sunlight still being able to reach Earth through lunar valleys, but no longer where mountains are present. Totality then begins with the diamond ring effect, the last bright flash of sunlight. Fig-5.

The writer is a former Professor, King Abdul Aziz University, Jeddah, Saudi Arabia.