﻿1 00:00:01,568 --> 00:00:05,005 A solar eclipse occurs when the moon moves between the Earth and 2 00:00:05,005 --> 00:00:09,826 the sun, blocks the sun’s light, and casts a shadow on the Earth. 3 00:00:09,826 --> 00:00:12,646 When the moon completely covers the bright disk of the sun, 4 00:00:12,646 --> 00:00:16,200 that’s a total solar eclipse, and it happens roughly every 5 00:00:16,200 --> 00:00:20,187 year and a half somewhere on Earth. A partial solar eclipse 6 00:00:20,187 --> 00:00:25,259 is more common, happening at least twice a year. A lunar 7 00:00:25,259 --> 00:00:28,045 eclipse, on the other hand, is where the moon moves behind the 8 00:00:28,045 --> 00:00:31,515 Earth, so it’s now the Earth blocking the sun’s light on the 9 00:00:31,515 --> 00:00:36,136 moon, creating a shadow on it with a red tint. The easy way to 10 00:00:36,136 --> 00:00:39,573 remember the difference is to remember what gets darker. With 11 00:00:39,573 --> 00:00:43,694 a solar eclipse, the sun gets darker, and during a lunar 12 00:00:43,694 --> 00:00:47,414 eclipse, the moon does. A solar eclipse is a rare event that not 13 00:00:47,414 --> 00:00:50,050 many get to see, because the moon’s shadow is relatively 14 00:00:50,050 --> 00:00:54,054 small. This limits the locations on Earth that get to see it. You 15 00:00:54,054 --> 00:00:58,408 have to be on the sunny side of the planet, and you have to be 16 00:00:58,408 --> 00:01:01,061 in the path of the moon’s shadow. So, if you find your 17 00:01:01,061 --> 00:01:05,098 area in the path of totality one year, you’ve hit the jackpot, 18 00:01:05,098 --> 00:01:08,068 because on average, that same spot on Earth will only get to 19 00:01:08,068 --> 00:01:12,072 see a solar eclipse every three hundred seventy-five years! 20 00:01:12,072 --> 00:01:16,944 During a solar eclipse, the moon casts a shadow with two parts: 21 00:01:16,944 --> 00:01:20,580 the umbra and penumbra. The moon’s umbra is the part of the moon’s 22 00:01:20,580 --> 00:01:24,551 shadow where the entire sun is blocked by the moon. In space, 23 00:01:24,551 --> 00:01:27,571 it’s a cone extending some four hundred thousand kilometers 24 00:01:27,571 --> 00:01:31,525 behind the moon. It’s when the small end of this cone hits the 25 00:01:31,525 --> 00:01:36,663 Earth that we experience a total solar eclipse. Most eclipse maps 26 00:01:36,663 --> 00:01:39,549 depicting the path will show you a circle representing the 27 00:01:39,549 --> 00:01:43,020 shadow of the moon, but in actuality, the true shape of the 28 00:01:43,020 --> 00:01:46,273 umbra is more like an irregular polygon with slightly curved 29 00:01:46,273 --> 00:01:50,661 edges. This is because the moon isn’t a perfect circle – it has 30 00:01:50,661 --> 00:01:54,047 mountains and valleys on its surface, which all affect the 31 00:01:54,047 --> 00:01:57,184 passing sunlight and subsequent shape of its shadow. And 32 00:01:57,184 --> 00:02:00,354 scientists now have a greater understanding of the shape of 33 00:02:00,354 --> 00:02:02,456 the moon’s surface, thanks to NASA’s Lunar Reconnaissance 34 00:02:02,456 --> 00:02:06,126 Orbiter. The unprecedented level of detail from the topographic 35 00:02:06,126 --> 00:02:10,130 maps, photos, and other datasets has allowed us to more precisely 36 00:02:10,130 --> 00:02:13,784 pinpoint the regions on Earth falling within the path of 37 00:02:13,784 --> 00:02:18,522 totality of a solar eclipse. So if you get the chance to witness 38 00:02:18,522 --> 00:02:22,326 a solar eclipse, always remember that our little moon plays a 39 00:02:22,326 --> 00:02:25,329 role that's quite large. 40 00:02:28,148 --> 00:02:33,153 [beeping]