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What Causes a Solar Eclipse? A Complete Scientific Explanation

What Causes a Solar Eclipse?
Long years ago, before Copernicus dared to defy the beliefs of Aristotle and Ptolemy, (and for a long time after that, too) people believed that eclipses were caused due to supernatural reasons! But Copernicus gave a logical explanation for the occurrence of eclipses, by putting the sun at the center of the universe, and angering a whole bunch of people.
Bidisha Mukherjee
Last Updated: Feb 17, 2018
In case you expect this article to be a supernatural entertainer, you are going to be sorely disappointed. I'm on Copernicus's side, so this article is going to explain the logical reasons for the occurrence of solar eclipses. If you are still interested, hang in there. There are diagrams and images, too!
How does a Solar Eclipse Occur?
Since the Moon revolves around the Earth and the Earth revolves around the Sun, there are times when the Sun, Moon and Earth are perfectly aligned in a straight line. Sometimes with the Earth coming between the Sun and Moon, and other times when the Moon comes between the Sun and the Earth. When the Earth is between the Sun and the Moon, we have a Lunar eclipse, and we'll talk about it some other time. Here I'm only going to explain what happens when the Moon comes between our planet and the Sun, i.e., Solar eclipse.

In a solar eclipse, as mentioned earlier, the Sun is either partially or fully obscured by the Moon. Since the Moon blocks the Sun, some areas of the Earth fall under the Moon's shadow. When that happens, the people living in those areas experience a Solar eclipse. But this is science and science is nothing if not interesting, with twists! So, the story doesn't end here. The Moon casts two types of shadows on the Earth when it blocks the Sun. Here is the explanation of these types:
Umbra: This is like complete blackout, and you can compare it to fully closed blinds, with a blanket thrown over them for extra measure! No light filters through. The areas on the Earth which fall in the umbra will experience a total solar eclipse, where the Sun is not visible at all. The Moon blocks it completely, and only the faint corona of the Sun is visible.
Penumbra: This is like pulling your blinds partially, so that some amount of sunlight is filtered through. In the areas of the Earth falling in the penumbra, the Moon blocks the Sun partially, so there is no complete blackout, and you can see part of the Sun. So these areas will experience either a partial or an annular solar eclipse. (We'll see what these types are in just a little bit.)
The umbra covers a very small region, whereas the penumbra covers a much larger area. Hence more people witness a partial or annular eclipse, rather than a total eclipse!

Now that we have an idea about how a solar eclipse occurs, we need to understand the rarity of this event! The Moon's orbit around the Earth is slightly tilted as compared to the Earth's orbit around the Sun. Well, the average tilt is 5.145º to be precise, but it may vary slightly depending on the exact position of the Moon. So, it takes a lot of effort for the Moon, Earth and the Sun to plan their schedule and align in a straight line so that we can be awed and entertained by the fantastic show that they put up for us! And, this only happens a few times in a year, minimum twice, and never more than 5 times. Out of which, a total eclipse will not occur more than twice a year.

Now let's see what are the types of solar eclipses that occur.
Types of Solar Eclipses
* Click on the diagrams to view the actual images.
In case of a total solar eclipse, the Moon looks as big as the Sun, thus covering it completely. For those few precious moments, only the faint halo/ corona of the Sun is visible. This happens when the Earth and the Moon are closest to each other, since then the Moon appears big enough to completely cover the Sun! It is a pretty rare event, not to mention spectacular, and is only for those people who are in the regions falling in the Moon's umbra.
This eclipse is caused when the Sun and the Moon are positioned in one straight line, but the Moon doesn't completely cover the Sun. During this eclipse, the Moon appears much smaller in size as compared to the Sun. As a result, a bright ring is visible in the sky. This happens when the Earth is farthest away from the Moon, which is why it appears small, and cannot hide the Sun completely. An annular eclipse occurs more frequently than a total eclipse, and needless to say, looks beautiful!
During this eclipse, the Sun and the Moon do not come in the same straight line. This happens because of the tilt of the Moon's orbit to the Earth's elliptic. In this eclipse, the Moon partly covers the Sun, so it is visible from a large portion of the Earth. In this type of eclipse the umbra of the Moon completely misses the Earth, so no region on Earth will experience a total solar eclipse. Only part of the penumbra covers a few regions of the Earth.
Hybrid Solar Eclipse
Hybrid solar eclipse is very, very rare, and it can be a total or an annular eclipse. You call an eclipse hybrid, if from some regions on the Earth it appears as a total eclipse, while from some other regions it appears to be annular!
The explanation is slightly complicated, but if you want to know, here it is...When the Moon is close to the Earth, it appears big. But due to the curvature of the Earth, it appears big from the center of the Earth and will appear to be comparatively smaller, from the sides of the curved surface. Which means, the umbra of the Moon will not reach the sides, causing an annular eclipse in the areas on the sides of the curvature, but as the umbra travels along the curvature and comes to a point where it reaches the Earth, it will cause a total solar eclipse in those parts. So, when a hybrid eclipse starts, it will appear annular, as it progresses it will appear to be total, and as it comes to an end, it will again appear to be annular! In the diagram of the partial solar eclipse above, imagine the umbra has traveled from the top to the position it is shown in. I assume it'll be easier to imagine now. Since the umbra is not reaching the surface of the Earth in that position, similarly, it wouldn't reach the Earth in the top position either. But as it travels from the top to the bottom, there will be a point when the umbra will reach the surface. Thus the top and bottom regions will experience an annular eclipse, while the central regions will experience a total eclipse! Cool, eh? Moving on to some trivia about solar eclipses!
Trivia about Solar Eclipses
■ The phenomena of a total solar eclipse is an exceptional event. On an average, at any specific region, such an event would repeat itself only once in 370 years.
■ The duration of a total eclipse is really very short. An eclipse will not last for more than 7 minutes, 31 seconds. This is because the Moon's umbra is moving at a speed of around 1700 kilometers per hour across the Earth's surface!
■ In the past millennium, not even 10 total solar eclipses lasted more than 7 minutes! The total eclipse that happened on June 30, 1973, was the last one that occurred for 7 minutes, 3.9 seconds. Such an eclipse, with a duration of more than 7 minutes will happen again on June 25, 2150.
■ The longest solar eclipse is going to occur on July 16, 2186, and will last for a record 7 minutes, 29 seconds! One of the longest solar eclipses of the 21st century occurred on July 22, 2009, lasting 6 minutes, 39 seconds.
Other than Earth, Jupiter, Mars, Uranus, Neptune and Pluto also experience solar eclipses. On Mars they last only for about 20 seconds!
■ A partial eclipse can occur twice in a month. In March of 1150 AD, two eclipses occurred. One on the 1st, and the other on the 30th.

Incredible phenomenon, right? Nature has a few tricks up its sleeve to awe and stun us, when we begin to forget our place! I am eagerly waiting for the next eclipse. You too, should find out when the next eclipse is going to occur in your area, and gear up for it! Not something you should miss!
Solar Eclipse phases
A solar eclipse on planet earth
Solar eclipse