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music

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What we're talking about is several visualizations of

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the path of the Moon's shadow during the eclipse in 2017.

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Everything in it is driven by the data, so the color of the

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ground, the position of the path of totality, the lighting from the sun,

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the sun angle. All of those are things that are based on data.

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A lot of NASA products were used to create this visualization. I used the

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Lunar Reconnaissance Orbiter--the laser altimetry data from that--

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which gives us a digital map of the elevations on the Moon.

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For the Earth I used something called SRTM, this was a radar that was flown on the space shuttle.

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For the positions of the Earth, the Moon, and the sun,

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I used a JPL ephemeris. An ephemeris is just a list

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of positions, but it's the most accurate tabulation

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of those positions. This visualization is unique because it shows the effect of both

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the irregular edge of the Moon, the limb of the Moon,

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we call it, and the elevation of the observer. Now, we've known for a long time

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that the elevation of the observer affects where the shadow is,

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and we've also known that the mountains and the valleys along the edge

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of the Moon affect the shadow. So, you may have seen on

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eclipse maps in the past that the image of the umbra,

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that shape of the shadow on the Earth, is drawn as a smooth oval, but

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we know that the Moon isn't smooth. Around the edge of the Moon, we have these sort of

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jagged peaks and valleys. And a peak can block the sun a little bit

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earlier than we thought, and a valley can let the sun in a few seconds

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longer than we thought. The combined effect of these peaks and valleys is to 

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create a shape that is not really an oval, it's more like a polygon.

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But it hasn't actually been seen in exactly this way before

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where we calculate those circumstances for every point on the map.

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and draw that shape. Totality is that

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two minutes--or two and a half minutes--when the Moon completely

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covers the sun. The sudden darkness of totality is just something 

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that a lot of people can't compare to anything else.

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I love the idea that I'm giving this kind of map to other people, and especially that

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it's more detailed and more accurate, so that people are actually in the right place 

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to see it. 

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tone

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beeping

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beeping