Year	Hours
1970-01-01	1835
1971-01-01	1813
1972-01-01	1780
1973-01-01	1766
1974-01-01	1745
1975-01-01	1728
1976-01-01	1674
1977-01-01	1638
1978-01-01	1602
1979-01-01	1580
1980-01-01	1580
1981-01-01	1570
1982-01-01	1559
1983-01-01	1553
1984-01-01	1548
1985-01-01	1542
1986-01-01	1538
1987-01-01	1511
1988-01-01	1513
1989-01-01	1510
1990-01-01	1503
1991-01-01	1500
1992-01-01	1510
1993-01-01	1507
1994-01-01	1505
1995-01-01	1488
1996-01-01	1483
1997-01-01	1478
1998-01-01	1476
1999-01-01	1474
2000-01-01	1455
2001-01-01	1429
2002-01-01	1414
2003-01-01	1401
2004-01-01	1421
2005-01-01	1423
2006-01-01	1420
2007-01-01	1426
2008-01-01	1429
2009-01-01	1411
2010-01-01	1424
2011-01-01	1427