Saturday, 12 August 2017

Eclipse Map Accuracy

Solar eclipse predictions are pretty accurate. They can get within a second or two of the time when the sky goes dark and the corona shines out. They can predict the location of the first spots of sunlight peeking through valleys along the lunar profile with reasonable accuracy. And these predictions can be made for many years in advance with good certainty.

So why do the headlines of some news items say they are wrong?

Those maps of eclipse’s path? ‘Wrong,’ experts say. And it’s the sun’s fault

Those maps of eclipse’s path? ‘Wrong,’ experts say — off by up to a half-mile at edge

Read more here: http://www.kansascity.com/news/local/article166394247.html#storylink=cpy

What is going on here? With accurate predictions decades in advance how could the calculators be wrong just a week before the eclipse? The problem is not in the math and not in the calculators per se. The problem is in figuring out just how big the Sun will appear in the sky.

You would think that astronomers would have a pretty handle on this size. They do. Within reasonable limits. You see it is not their fault, it is the Sun itself. The Sun is a ball of gas and getting a good measurement is not all that easy. It is a moving target in a way. Just where is the edge? What do we define as the edge? Is it uniform in size all the time? These questions make the job a tough one.

So would you like to help figure this puzzle out? Some of the scientists at the International Occultation Timing Association (they time things getting in the way such as when the Moon passes in front of a star) have an experiment they'd like you to do, with your cell phone, to help measure the size of the shadow and thus the solar disk.

Of course, following this information set my imagination running and here are some new cartoons on the subject.
Cave Painter
Solar System Conversation

Bottom line: The northern and southern "GRAZING" zones are not a sharp edge. To see the total solar eclipse, be at least a kilometer inside this lines!



Read more here: http://www.miamiherald.com/news/nation-world/national/article166457627.html#storylink=cpy
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