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why do we observe solar and lunar eclipses

Asked by: Liza Dennis, Brighton
Solar eclipses are not actually rarer than lunar eclipses in fact, they occur in about equal numbers, usually about two of each per year. For example, between 2000BC to 3000AD there will be 11,898 solar eclipses and 12,064 lunar eclipses. However, at any one location on Earth, it is much less common to see a solar eclipse than a lunar one. And the reason for this is entirely due to geometry. A lunar eclipse, when the Moon moves through the shadow of the Earth, is visible from wherever the Moon is above the horizon, which is over half of the Earth. However, when the Moon appears to move in front of the Sun during a solar eclipse, the shadow cast by the Moon is much smaller than Earth. Its only about 480km (300 miles) wide when cast onto the Earths surface. Solar eclipses are therefore only visible from within a narrow path across the Earth, making it difficult to get to a location to see one.


This is why they are visible less often from any given location. Subscribe to for fascinating new Q As every month and follow on Twitter for your daily dose of fun facts. There are several lunar and solar eclipses in the course of every year. Which are more common? That depends on what types of lunar eclipses you decide to include in the final tally. Letвs define terms. A total solar eclipse happens when the moon passes in front of the sun в like the one coming up on в blotting it from view. During a total lunar eclipse the moon totally passes through Earthвs dark umbral shadow and often exhibits a coppery red color. The image at top shows a total lunar eclipse. But thereвs more than one type of solar eclipse, and lunar eclipse. There are the partial phases of each, of course. And thereвs also a penumbral lunar eclipse, like the one shown at right. The left-side image shows a moon in penumbral eclipse.


The right-side image shows a full moon with no eclipse. See the difference? A penumbral lunar eclipse is a very subtle kind of eclipse. Hereвs how it happens. There are two parts to Earthвs shadow: a dark inner umbra and a lighter outer penumbra. And so there are two kinds of lunar eclipse: umbral and penumbral. A penumbral eclipse happens when Earthвs lighter outer shadow brushes the moonвs face. Some people say they canвt perceive a penumbral eclipse even as itвs happening. From the moon, the eclipse would be much more obvious, for you would see the Earth partially eclipsing or blocking out the sun. In fact, when youвre watching a partial solar eclipse from Earth, youвre standing in the moonвs penumbral shadow. So which is more common, a solar eclipse or a lunar eclipse? Itвs sometimes said that on a worldwide scale solar eclipses outnumber lunar eclipses by about a three to two margin. But that figure completely ignores penumbral lunar eclipses.


When you include penumbral lunar eclipses, the number of solar and lunar eclipses is almost the same. In fact, once you include penumbral eclipses, lunar eclipses slightly outnumber solar eclipses. In his classic book More Mathematical Astronomical Morsels, the famous Belgium astronomer Jean Meeus reported that there were 228 solar eclipses and 229 lunar eclipses in the 20th century, from the years 1901 to 2000. For the years 1 to 3000, Jean Meeus figures there are 7,124 solar eclipses and 7,245 lunar eclipses. And for the 5,000-year period from 2000 B. C. to A. D. 3000, NASAвs Fred Espenak в sometimes known as Mr. Eclipse в finds 11,847 solar and 12,186 lunar eclipses. By the way, all solar eclipses happen at new moon, when the moon passes more or less between the Earth and sun. During a total solar eclipse, a rim of twilight encircles your entire horizon, the sky turns dark and stars pop into view.


Meanwhile, in the sky, the sunвs fiery corona can be seen surrounding the dark orb в the moon в that is completely covering the sun. All lunar eclipses happen at full moon, when Earthвs dark shadow totally or partially covers the moon. They are less dramatic than solar eclipses, but no less wonderful. You see Earthвs shadow on the moonвs face as a dark вbiteв taken out of the moon. This darkness creeps across the moonвs face during the several hours of the eclipse. Both solar eclipses and lunar eclipses are beautiful, in their own way! Bottom line: Itвs sometimes said that, on a worldwide scale, solar eclipses outnumber lunar eclipses by about a three to two margin. But that doesnвt count penumbral eclipses. When you include penumbral lunar eclipses, the number of solar and lunar eclipses is almost the same, with lunar eclipses slightly outnumbering solar eclipses.

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