Solar eclipses occur when the moon moves between the Sun and the Earth, temporarily obscuring sight of the Sun. For many, they are awe-inspiring events that bring the realities of nature and the universe around us to our doorstep. There are four main types of solar eclipses and they are explained below.
History of Eclipses
Because of the relatively well understood nature of the movement of the moon, Earth and the Sun, eclipses are relatively easy to predict. With this in mind, when major historical events occurred in close proximity chronologically to eclipses, it becomes very easy to verify the events occurrence and the historical accuracy of accounts related to the event.
One notable example involves the eclipses at Sardis in 478 BCE and in Sparta in 477 BCE. It verifies the historical accuracy of writings about Xerxes attack on Greece, as recorded by Herodotus.
Eclipses have also served as mystical, religious and astrological signs for many cultures over the millenia. Some have taken a more scientific approach, calculating the exact cycle of eclipses and relating them to crop cycles and the fertility of the Earth.
Eclipses are very dangerous to view unaided. Staring directly at the bright disk of the sun, known as the protosphere, causes permanent damage to the retina, usually resulting in visual impairment and blindness. During an eclipse, the Sun is covered so it's far easier to stare without noticing harm, despite the fact that it is just as dangerous. Some form of eye protection is a must for viewing a solar eclipse.
Types of Eclipses
The event where the Sun is completely blocked by the moon is known as a total eclipse. The moon's dark shadow completely overtakes the sun in the sky, with a faint corona. The corona is the "plasma atmosphere" of the sun. During an eclipse, only a small region of the surface of the Earth is able to see the total eclipse. A total eclipse occurs somewhere on Earth every 18 months, on average. However, many of these can occur over regions of ocean or the antarctic, making viewing nearly impossible. Mathematically, a region is estimated to see a repeat total eclipse every 370 years, making this a very rare occurrence. They last only a few minutes long, with very few lasting more than 7 minutes (once every 100 years).
An annular eclipse occurs when the moon is blocking part of the sun and is perfectly in line, but the size of the moon is such that it does not cover the entire sun. The bright ring that is formed by the sun is referred to as an annulus.
Hybrid eclipses are rare occurrences are when certain regions of the Earth can see a total eclipse and other regions can only see an annular eclipse. Partial eclipses, on the other hand, occur when the moon only partially blocks the sun because the two bodies are not perfectly in line. Large portions of the Earth can usually see this when a small portion is witnessing the annular or total eclipse. Because of the angle of view, some partial eclipses are only visible as partial eclipses, without an accompanying annular or total eclipse.
Many worldwide travel to regions to witness the rarer of the eclipse events, specifically the total eclipses. Because of the elliptical nature of planetary orbits, certain months of the year favor total eclipses over alternative eclipse events. The aphelion, in July, is the period when the Earth is farthest from the Sun and often results in total eclipses (the Sun is smaller relative to the moon and can be fully obscured). In January, known as the perihelion, the Sun is closer and annular eclipses are much more likely.