1 00:00:00,010 --> 00:00:07,020 [ Music ] 2 00:00:07,040 --> 00:00:13,580 Like clockwork, the full Moon appears every month in our sky, a sight so familiar that we often take it for granted, 3 00:00:13,600 --> 00:00:20,010 but about twice a year, over the course of a few hours, the full Moon sports a decidedly different look. 4 00:00:20,030 --> 00:00:26,150 What causes this sudden change? A lunar eclipse occurs when the Moon passes through the Earth's shadow, 5 00:00:26,170 --> 00:00:30,800 just as a solar eclipse occurs when part of the Earth passes through the Moon's shadow. 6 00:00:30,820 --> 00:00:37,980 But the Moon circles the Earth every month as it cycles through its phases, lining up at both full Moon and new Moon. 7 00:00:38,000 --> 00:00:44,240 So why don't eclipses happen twice a month? The reason is that the Moon's orbit around the Earth is tilted 8 00:00:44,260 --> 00:00:50,280 relative to the Earth's orbit around the Sun. Although the Earth and the Moon always cast long shadows, 9 00:00:50,300 --> 00:00:54,430 they rarely shade each other thanks to the Moon's orbital tilt. 10 00:00:54,450 --> 00:00:57,830 But if that's the case, why do eclipses happen at all? 11 00:00:57,850 --> 00:01:05,360 Throughout the year, the Moon's orbital tilt remains fixed with respect to the stars, meaning that it changes with respect to the Sun. 12 00:01:05,380 --> 00:01:12,780 About twice a year, this puts the Moon in just the right position to pass through the Earth's shadow, causing a lunar eclipse. 13 00:01:12,800 --> 00:01:18,480 As the Moon passes into the central part of the Earth's shadow, called the umbra, it darkens dramatically. 14 00:01:18,500 --> 00:01:25,180 Once it's entirely within the umbra, the Moon appears a dim red due to sunlight scattered through the Earth's atmosphere. 15 00:01:25,200 --> 00:01:28,580 In fact, if you watched the eclipse from the surface of the Moon, 16 00:01:28,600 --> 00:01:33,640 you'd see the Sun set behind the entire Earth, bathing you in a warm red glow. 17 00:01:33,660 --> 00:01:40,130 Back home, you'll have to stay up late to watch a lunar eclipse, but if you do you'll see the Moon in rare form, 18 00:01:40,150 --> 00:01:46,500 and you'll catch a brief glimpse of our own planet's long shadow. 19 00:01:46,520 --> 00:01:58,365 [ satellite beeping ]