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What we're talking about is several visualizations of
the path of the Moon's shadow during the eclipse in 2017.
Everything in it is driven by the data, so the color of the
ground, the position of the path of totality, the lighting from the sun,
the sun angle. All of those are things that are based on data.
A lot of NASA products were used to create this visualization. I used the
Lunar Reconnaissance Orbiter--the laser altimetry data from that--
which gives us a digital map of the elevations on the Moon.
For the Earth I used something called SRTM, this was a radar that was flown on the space shuttle.
For the positions of the Earth, the Moon, and the sun,
I used a JPL ephemeris. An ephemeris is just a list
of positions, but it's the most accurate tabulation
of those positions. This visualization is unique because it shows the effect of both
the irregular edge of the Moon, the limb of the Moon,
we call it, and the elevation of the observer. Now, we've known for a long time
that the elevation of the observer affects where the shadow is,
and we've also known that the mountains and the valleys along the edge
of the Moon affect the shadow. So, you may have seen on
eclipse maps in the past that the image of the umbra,
that shape of the shadow on the Earth, is drawn as a smooth oval, but
we know that the Moon isn't smooth. Around the edge of the Moon, we have these sort of
jagged peaks and valleys. And a peak can block the sun a little bit
earlier than we thought, and a valley can let the sun in a few seconds
longer than we thought. The combined effect of these peaks and valleys is to
create a shape that is not really an oval, it's more like a polygon.
But it hasn't actually been seen in exactly this way before
where we calculate those circumstances for every point on the map.
and draw that shape. Totality is that
two minutes--or two and a half minutes--when the Moon completely
covers the sun. The sudden darkness of totality is just something
that a lot of people can't compare to anything else.
I love the idea that I'm giving this kind of map to other people, and especially that
it's more detailed and more accurate, so that people are actually in the right place
to see it.
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