A rare alignment of events allows Earthlings to witness not just solar eclipses, but what we might call perfect solar eclipses. Such an eclipse depends on just the right sizes, shapes, and relative distances of the Sun, Moon, and Earth. There are 65 major moons in our Solar System, and many smaller ones. But only we enjoy perfect solar eclipses.
The Moon is about times smaller than the Sun. But the Moon is also about times closer to the Earth than is the Sun. As a result, the size of the Moon on our sky matches the size of the Sun. And since they appear as round disks, they match in both size and shape.
The Moon is slowly moving away from Earth — at roughly the same speed that fingernails grow. In brief, the best time and place to view total solar eclipses in our Solar System is just when and where there are observers to see them. As it happens, this precise arrangement of Earth, Moon, and Sun helps sustain life on Earth. Let me explain.
For lots of reasons , a planet almost surely needs liquid water on its surface to host complex life. Most places in the Solar System, and in the universe, are either way too hot or way too cold.
Think of this zone as a narrow, nearly circular ring of space around a star. The Earth is, of course, safely inside the zone. But how narrow is it? To figure that out, we need only look at our closest planetary neighbors. The fact that the sun appears dim, or that you feel no discomfort when looking at the sun through these types of filters, is no guarantee that your eyes are safe.
There is one time when you can safely look directly at the sun: during a total eclipse, when the sun's disk is entirely covered. During those few precious seconds or minutes, the magnificent corona shines forth in all its glory surrounding the darkened sun; a marvelous fringe of pearly white light.
It differs in size, in tints and patterns from eclipse to eclipse. It is always faint and delicate, with a sheen like a pale aurora. It has a variable appearance. Sometimes it has a soft continuous look; at other times, long rays of it shoot out in three or four directions. It may stand out from the disk in filmy petals and streamers.
But when the sun begins to again emerge into view, the corona quickly disappears and you'll need to protect your eyes once again. As best as we can determine, the earliest record of a solar eclipse occurred over four millennia ago. In China, it was believed that the gradual blotting out of the sun was caused by a dragon who was attempting to devour the sun, and it was the duty of the court astronomers to shoot arrows, beat drums and raise whatever cacophony they could to frighten the dragon away.
In the ancient Chinese classic Shujing or Book of Documents is the account of Hsi and Ho, two court astronomers who were caught completely unaware by a solar eclipse, having gotten drunk just before the event began.
In the aftermath, Zhong Kang, the fourth emperor of the Xia dynasty ordered that Hsi and Ho be punished by having their heads chopped off. The eclipse in question was that of Oct. In the Bible, in the book of Amos , are the words, "I will cause the sun to go down at noon, and I will darken the Earth in the clear day. An Assyrian tablet also attests to the event.
According to the historian Herodotus, there was a five-year war that raged between the Lydians and the Medes. As the war was about to move into its sixth year, a Greek sage, Thales of Miletus foretold to the Ionians that the time was soon approaching when day would turn to night. On May 17, B. And giving new meaning to the term "scared to death," is the timid emperor Louis of Bavaria, the son of Charlemagne, who witnessed an unusually long total eclipse of the sun on May 5, A.
But no sooner had the sun begun to emerge back into view, Louis was so overwhelmed by what he had just seen that he died of fright. Samuel Williams, a professor at Harvard, led an expedition to Penobscot Bay, Maine, to observe the total solar eclipse of Oct. As it turned out, this eclipse took place during the Revolutionary War, and Penobscot Bay lay behind enemy lines. Fortunately, the British granted the expedition safe passage, citing the interest of science above political differences.
Williams apparently made a crucial error in his computations and inadvertently positioned his men at Islesboro — just outside the path of totality — likely finding this out with a heavy heart when the narrowing crescent of sunlight slid completely around the dark edge of the moon and then started to thicken!
During a total solar eclipse, a few ruby-red spots may seem to hover around the jet-black disk of the moon. Those are solar prominences, tongues of incandescent hydrogen gas rising above the surface of the sun.
During the total eclipse of Aug. Two English astronomers, J. Norman Lockyer and Edward Frankland, later named it " helium ," from the Greek helios the sun.
The gas was not identified on Earth until And because sunlight is blocked during a total eclipse, some of the brighter stars and planets can be observed in the darkened sky. Under such conditions astronomers were able to test part of Einstein's now-celebrated general theory of relativity. That theory predicted that light from stars beyond the sun would bend from a straight path in a certain way as it passed the sun.
Our modern technology now allows astronomers to make most of the observations that once had to await an eclipse. But a total eclipse of the sun will always remain among the most impressive of natural spectacles and is a sight that will always be remembered. Be sure to put it on your bucket list; you will not be disappointed.
Editor's Note: If you snap an amazing solar eclipse photo and would like to share it with Space. Follow us on Twitter Spacedotcom and on Facebook. Join our Space Forums to keep talking space on the latest missions, night sky and more! And if you have a news tip, correction or comment, let us know at: community space. See all comments 4. Admin said:. If I'm 14 years old will I get to see another solar eclipse? I was born August 11, The apparent or angular sizes of both the Sun and Moon vary slightly from time to time as their distances from Earth vary.
Figure 1 shows the distance of the observer varying at points A—D, but the idea is the same. Much of the time, the Moon looks slightly smaller than the Sun and cannot cover it completely, even if the two are perfectly aligned. However, if an eclipse of the Sun occurs when the Moon is somewhat nearer than its average distance, the Moon can completely hide the Sun, producing a total solar eclipse. Figure 2: Geometry of a Total Solar Eclipse.
The Sun is drawn at lower left and the Earth at upper right. The geometry of a total solar eclipse is illustrated in Figure 2. The thin zone across Earth within which a total solar eclipse is visible weather permitting is called the eclipse path.
Within a region about kilometers on either side of the eclipse path, a partial solar eclipse is visible. The duration of totality may be only a brief instant; it can never exceed about 7 minutes. Because a total eclipse of the Sun is so spectacular, it is well worth trying to see one if you can.
As a result, eclipse chasing is rarely within the budget of a typical college student. Nevertheless, a list of future eclipses is given for your reference in Future Total Eclipses , just in case you strike it rich early. And, as you can see in the Appendix, there will be total eclipses visible in the United States in and , to which even college students may be able to afford travel.
What can you see if you are lucky enough to catch a total eclipse? A partial phase follows, during which more and more of the Sun is covered by the Moon. About an hour after the eclipse begins, the Sun becomes completely hidden behind the Moon. In the few minutes immediately before this period of totality begins, the sky noticeably darkens, some flowers close up, and chickens may go to roost.
As an eerie twilight suddenly descends during the day, other animals and people may get disoriented. During totality, the sky is dark enough that planets become visible in the sky, and usually the brighter stars do as well.
The corona thin outer atmosphere of the Sun is visible during a total solar eclipse. It looks more extensive in photographs than it would to the unaided eye. It is ordinarily not visible because the light of the corona is feeble compared with the light from the underlying layers of the Sun. The total phase of the eclipse ends, as abruptly as it began, when the Moon begins to uncover the Sun. Gradually, the partial phases of the eclipse repeat themselves, in reverse order, until the Moon has completely uncovered the Sun.
We should make one important safety point here: while the few minutes of the total eclipse are safe to look at, if any part of the Sun is uncovered, you must protect your eyes with safe eclipse glasses [1] or by projecting an image of the Sun instead of looking at it directly.
For more, read the How to Observe Solar Eclipses section of this chapter. A lunar eclipse occurs when the Moon enters the shadow of Earth. The geometry of a lunar eclipse is shown in Figure 4. Unlike a solar eclipse, which is visible only in certain local areas on Earth, a lunar eclipse is visible to everyone who can see the Moon. Because a lunar eclipse can be seen weather permitting from the entire night side of Earth, lunar eclipses are observed far more frequently from a given place on Earth than are solar eclipses.
Figure 4: Geometry of a Lunar Eclipse.
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