What is a solar eclipse? Types and how to observe safely
A solar eclipse is one of the most spectacular celestial events that people get to experience from Earth. The Moon slowly turns broad daylight into night as it glides in front of the Sun, hiding it from view. If the eclipse is total, then at mid-eclipse, the Sun completely vanishes, but its ephemeral corona surrounds the blackened Moon like a crown.
A solar eclipse occurs when the Moon comes between the Earth and the Sun, and casts its shadow on the Earth. For obvious reasons, an eclipse of the Sun can happen only when the Moon is new, and thus lies on the Sun-side of the Earth. If the Moon’s orbit lay in the same plane as that of the Earth, there would be an eclipse every month. However, because the lunar orbit is tilted at an angle of about five degrees, most times, the New Moon passes unseen either above or below the Sun in the sky, creating no eclipse.
Types of Solar Eclipses
Solar eclipses are of three types: total, partial, and annular. Which kind you see depends on what part of the Moon’s shadow passes over you and the distance between the Earth and the Moon at the time of the eclipse.
Total Solar Eclipses
Total solar eclipses are the result of a fortunate coincidence. Because the Sun and the Moon are almost exactly the same angular size as we see them from Earth, during a total eclipse, the Moon covers the bright disk of the Sun, but little or none of the surrounding space. This allows us to see features of the Sun that would otherwise be invisible, except from outer space. These include the glorious corona, which stretches outwards from the Sun in all directions, and solar prominences – large arch-shaped structures observable in the corona.
Total eclipses can be observed only within the region of totality, a very narrow band – up to 169 miles wide – where the Moon’s shadow falls as the Earth rotates. For this reason, total eclipses are rare events in any given geographical area, and it is no wonder that many eclipse-tour companies have sprung up, making it easy for any eclipse-chaser to experience the greatest sight of his lifetime.
Partial Solar Eclipses
Much more common are partial solar eclipses, in which the Moon obscures only part of the Sun. Observers located in the much broader outer shadow of the Moon (the penumbra) see such an eclipse. At the edge of the penumbra, the Moon seems to take a 'bite' out of the Sun. Further within the penumbra, the Sun’s disk takes the shape of a crescent. Unfortunately, a partial eclipse is not as dramatic as a total eclipse; even with three-quarters of the Sun covered by the Moon, daylight still looks quite ordinary.
Annular Eclipses
A special case of a solar eclipse is known as an annular eclipse. This occurs when the Moon is farther from the Earth than normal, and hence, its apparent size is not quite sufficient to cover the Sun completely. Therefore, even though the Sun-Moon alignment is perfect, the Moon will appear slightly smaller in diameter than the Sun, and a thin ring of sunlight will remain visible around the dark silhouette of the Moon. The name annular eclipse comes from the Latin annulus, meaning ring.
How to watch?
The greatest care must be taken when watching a solar eclipse – but nobody should ever pass up the chance to see the splendor of such a celestial event. Never look at the Sun unless you wear special solar eclipse eyeglasses, and even more importantly, make sure you have the proper filters if you plan to observe the Sun through a telescope. It is because looking at the Sun directly during an eclipse can cause serious, irreversible eye injuries. Always go for protective gear!
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