Monday, 19 December 2016

Greatest Eclipse - a strange term

You may have noticed the term Greatest Eclipse appearing on some maps of the total solar eclipse path. Perhaps you already know what that means.

Recently, some questions came up related to this term in the SEML, an open discussion group of eclipse enthusiasts. My initial reaction was to try to define the terms being used [see previous blog entry] but after further consideration and some guidance from some great minds I am revising my feelings.

The term is meaningless for total solar eclipse chasers unless one wants to say they are at the best place for syzygy.

Syzygy is the alignment of three astronomical bodies such as the Sun, Earth, and Moon. During perfect syzygy an eclipse takes place.


So if you want to experience the greatest syzygy, then the Greatest Eclipse point is the place to be!

The term "greatest eclipse" indicates that the cone of the lunar shadow is closest to the center of the Earth. For a total solar eclipse this point is somewhat near the center of the central path. It all depends on the inclination of the Earth to the Ecliptic, latitude of the observer, and so on. Really, it is not the greatest point to see the eclipse, but it is normally a good one - if the sky is clear.

For a partial solar eclipse, the greatest eclipse point is where the maximum eclipse coverage will be seen. So for that context, a partial solar eclipse, the point makes sense. But it really does not hold much interest for total solar eclipses. Especially if compared to duration which is very important for some.



Seeing a total solar eclipse is not about the amount of time you see one. No matter how many minutes the total eclipse is predicted to last, it will seem like just a few seconds. There are those who have seen over two dozen eclipses that will tell you that every eclipse seems to last about 15 seconds. The key thing is to see it! It really is a surreal experience. Once you see one, you know, and then you might want to add more time by going to another and another. Some of us keep on going, we can never get enough! See the eclipse-chasers log. Only a few have reached over a half hour of total eclipse observing!


I often tell people that as an amateur astronomer I can stare at the Moon or Saturn or Jupiter for hours and not get bored with the view. They are amazing to behold themselves. A solar eclipse - well, I have seen just under one hour of totality so far. I've looked at Saturn longer than that in a single night! Truth is, once you see one, you want to see another one.

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