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- Season 0 1999-07-13
- Season 1 1974-03-03
- Season 2 1974-11-03
- Season 3 1976-01-04
- Season 4 1977-01-05
- Season 5 1978-01-04
- Season 6 1979-01-04
- Season 7 1980-01-15
- Season 8 1981-01-06
- Season 9 1982-01-10
- Season 10 1983-01-18
- Season 11 1984-01-17
- Season 12 1985-01-15
- Season 13 1986-01-21
- Season 14 1987-01-20
- Season 15 1988-01-19
- Season 16 1989-01-17
- Season 17 1990-01-09
- Season 18 1991-01-08
- Season 19 1992-01-14
- Season 20 1993-01-05
- Season 21 1994-01-18
- Season 22 1995-01-08
- Season 23 1995-10-10
- Season 24 1996-10-01
- Season 25 1997-10-07
- Season 26 1998-10-06
- Season 27 1999-10-05
- Season 28 2000-10-24
- Season 29 2001-10-02
- Season 30 2002-09-03
- Season 31 2003-09-30
- Season 32 2004-09-28
- Season 33 2005-09-20
- Season 34 2006-09-05
- Season 35 2007-10-09
- Season 36 2008-10-07
- Season 37 2009-10-06
- Season 38 2010-10-19
- Season 39 2011-09-07
- Season 40 2012-10-10
- Season 41 2013-09-11
- Season 42 2014-09-10
- Season 43 2015-09-16
- Season 44 2016-09-07
- Season 45 2018-01-10
- Season 46 2019-01-02
- Season 47 2020-02-05
- Season 48 2021-01-13
- Season 49 2022-02-01
- Season 50 2023-02-01
- Season 51 2024-01-31
Season 51 Episode
- Season 47 Polar Extremes
- Season 47 Dog Tales
- Season 47 Cat Tales
- Season 47 Mysteries of Sleep
- Season 47 Cuba's Cancer Hope
- Season 47 The Truth About Fat
- Season 47 Decoding COVID-19
- Season 47 Eagle Power
- Season 47 Human Nature / Gene-Editing Reality Check
- Season 47 Secret Mind of Slime
- Season 47 A to Z: The First Alphabet
- Season 47 A to Z: How Writing Changed the World
- Season 47 Nature's Fear Factor
- Season 47 Touching the Asteroid
- Season 47 Can We Cool the Planet?
- Season 47 Saving Notre Dame
NOVA - Season 47 Episode 4 Mysteries of Sleep
6.85 55 minutes From fruit flies to whales, virtually every animal sleeps. But why? Why do we need to spend nearly a third of our lives in such a defenseless state? Scientists are peering more deeply into the sleeping brain than ever before, discovering just how powerful sleep can be, playing a role in everything from memory retention and emotional regulation to removing waste from our brains.
