ECLIPSES, whether solar or lunar, have forever been enigmatic, perplexing and among the least understood of all celestial phenomena. The basic thing that we must understand is that any, or any kind of eclipse, is the result of hide and seek the three bodies play with each other.

Eclipses have blighted humanity for thousands of years. For their failure to predict them, many court ‘astronomers’ had to pay dearly for their inability. Science is forever at the beck and call of whoever cares to avail of its services. Men like Galileo, Leonardo da Vinci, Newton, Halley, Kepler, Einstein and numerous others in various branches of science, and philosophy did just that. They caught the bull by the horns and came up with answers to a myriad of questions that gradually transformed the lives of the peoples in the world.

Just as the great astronomers and other scientists of the world, we shall take a close look at why, after all, do eclipses take place — that is the real, hard core scientific reasons.

For any eclipse to occur, the three bodies have to be in a straight line, in such a manner that their centres are in one straight line — totally, or partially. As you know, the apparent (not real) diameters of Sun and full Moon are very nearly the same. Never ever believe that they have the same diameter for one is almost infinitely bigger than the other. Just imagine that the Sun can accommodate more than 1,300 Earths laid side by side. At the same time, the Earth is several times bigger than Moon (Sun is 400 times larger than the Moon, however, it is 400 times farther away).

A solar eclipse occurs as the Moon moves between the Earth and Sun. If it covers the Sun completely, it forms total solar eclipse. If the Moon covers only part of the Sun, it is partial solar eclipse.

What comes next needs some concentration of mind to understand. Like any shadow, Moon’s shadow consists of a central ‘umbra’ of total shadow and a penumbra of partial shadow. What we happen to see when Moon crosses in front of the Sun depends on where we are in the Moon’s shadow.

Moon’s umbral shadow produces a spot of darkness only 269km in diameter on Earth’s surface. If we come under that spot of total shadow, we see a total solar eclipse. If we are just outside the umbral shadow but still in penumbra, we see only a part of the Sun peeping from around the Moon, and the eclipse is partial. However, if we are outside the penumbra we see no eclipse at all.

The shadow of the Moon sweeps across the Earth at 1,700km/h. To be able to see a total solar eclipse, we must be in the path of totality or the umbral spot. A total solar eclipse begins when we first see the edge of the Moon encroaching upon Sun.

For the understanding of eclipses we must first understand the umbra and penumbra which are caused by (a) the shadow of Moon upon Earth, and (b) the orbital movement of the Moon.

During the partial eclipse, part of Sun is visible but it is extremely dangerous to look at the Sun without adequate protection. Even very dense filters and exposed negatives are not safe because they can still burn the retina of our eyes. The damage would be permanent. Though the Sun is just a little less dangerous during an eclipse, yet the damage to the eyes would be catastrophic. Very special filters made from several layers of negatives may be used for the purpose.

Yes! Totality is a spectacular sight. You already know about photosphere, prominences, corona and chromosphere from previous articles. So these effects become prominent during totality.

Another remarkable sight is the annular eclipse. A bright ring of photosphere (sun’s clearly visible bright disc) remains visible along the edges of the Moon. Interestingly, solar eclipses can occur when the Moon is new, and lunar eclipse can only occur when the Moon is full. If the Moon is completely immersed in the umbra, the central shadow, then eclipse is said to be total. Moon glows coppery red due to sunlight as it passes through Earth’s atmosphere. If the Moon enters the umbral shadow only partly, the eclipse is partial and the reddish glow is not visible.

To be able to see a total eclipse, we must be in the path of totality, the path swept out by the umbra of the Moon.

There is so much more to the mechanics of eclipses, but we are laid low by the demon of paucity of space to proceed any further on the matter.

Next we shall examine the ‘extras’ of space: asteroids, meteors, shooting stars and meteorites. Until then goodbye and God bless!