1 00:00:00,000 --> 00:00:04,020 music 2 00:00:04,040 --> 00:00:08,160 What we're talking about is several visualizations of 3 00:00:08,180 --> 00:00:12,360 the path of the Moon's shadow during the eclipse in 2017. 4 00:00:12,380 --> 00:00:16,530 Everything in it is driven by the data, so the color of the 5 00:00:16,550 --> 00:00:20,700 ground, the position of the path of totality, the lighting from the sun, 6 00:00:20,720 --> 00:00:24,840 the sun angle. All of those are things that are based on data. 7 00:00:24,860 --> 00:00:28,930 A lot of NASA products were used to create this visualization. I used the 8 00:00:28,950 --> 00:00:33,100 Lunar Reconnaissance Orbiter--the laser altimetry data from that-- 9 00:00:33,120 --> 00:00:37,290 which gives us a digital map of the elevations on the Moon. 10 00:00:37,310 --> 00:00:41,360 For the Earth I used something called SRTM, this was a radar that was flown on the space shuttle. 11 00:00:41,380 --> 00:00:45,440 For the positions of the Earth, the Moon, and the sun, 12 00:00:45,460 --> 00:00:49,590 I used a JPL ephemeris. An ephemeris is just a list 13 00:00:49,610 --> 00:00:53,790 of positions, but it's the most accurate tabulation 14 00:00:53,810 --> 00:00:57,980 of those positions. This visualization is unique because it shows the effect of both 15 00:00:58,000 --> 00:01:02,090 the irregular edge of the Moon, the limb of the Moon, 16 00:01:02,110 --> 00:01:06,190 we call it, and the elevation of the observer. Now, we've known for a long time 17 00:01:06,210 --> 00:01:10,230 that the elevation of the observer affects where the shadow is, 18 00:01:10,250 --> 00:01:14,400 and we've also known that the mountains and the valleys along the edge 19 00:01:14,420 --> 00:01:18,540 of the Moon affect the shadow. So, you may have seen on 20 00:01:18,560 --> 00:01:22,710 eclipse maps in the past that the image of the umbra, 21 00:01:22,730 --> 00:01:26,830 that shape of the shadow on the Earth, is drawn as a smooth oval, but 22 00:01:26,850 --> 00:01:30,950 we know that the Moon isn't smooth. Around the edge of the Moon, we have these sort of 23 00:01:30,970 --> 00:01:35,020 jagged peaks and valleys. And a peak can block the sun a little bit 24 00:01:35,040 --> 00:01:39,100 earlier than we thought, and a valley can let the sun in a few seconds 25 00:01:39,120 --> 00:01:43,220 longer than we thought. The combined effect of these peaks and valleys is to 26 00:01:43,240 --> 00:01:47,370 create a shape that is not really an oval, it's more like a polygon. 27 00:01:47,390 --> 00:01:51,430 But it hasn't actually been seen in exactly this way before 28 00:01:51,450 --> 00:01:55,550 where we calculate those circumstances for every point on the map. 29 00:01:55,570 --> 00:01:59,680 and draw that shape. Totality is that 30 00:01:59,700 --> 00:02:03,750 two minutes--or two and a half minutes--when the Moon completely 31 00:02:03,770 --> 00:02:07,860 covers the sun. The sudden darkness of totality is just something 32 00:02:07,880 --> 00:02:12,010 that a lot of people can't compare to anything else. 33 00:02:12,030 --> 00:02:16,160 I love the idea that I'm giving this kind of map to other people, and especially that 34 00:02:16,180 --> 00:02:20,360 it's more detailed and more accurate, so that people are actually in the right place 35 00:02:20,380 --> 00:02:24,400 to see it. 36 00:02:24,420 --> 00:02:28,580 tone 37 00:02:28,600 --> 00:02:32,670 beeping 38 00:02:32,690 --> 00:02:33,834 beeping