Graph
| Year | Totals | Observation hours |
|---|---|---|
| 1983 | 0 | 9:15 |
| 1984 | 2 | 27:20 |
| 1985 | 1 | 29:00 |
| 1986 | 5 | 69:40 |
| 1987 | 5 | 47:00 |
| 1988 | 2 | 17:30 |
| 1989 | 4 | 45:00 |
| 1990 | 0 | 35:30 |
| 1991 | 1 | 48:28 |
| 1992 | 0 | 45:00 |
| 1993 | 1 | 51:30 |
| 1994 | 1 | 27:30 |
| 1995 | 1 | 50:00 |
| 1996 | 1 | 49:15 |
| 1997 | 0 | 34:50 |
| 1998 | 1 | 50:00 |
| 1999 | 3 | 57:20 |
| 2000 | 1 | 42:30 |
| 2001 | 2 | 69:35 |
| 2002 | 1 | 76:40 |
| 2003 | 0 | 108:30 |
| 2004 | 1 | 111:45 |
| 2005 | 2 | 145:21 |
| 2006 | 5 | 152:17 |
| 2007 | 1 | 187:59 |
| 2008 | 0 | 132:42 |
| 2009 | 1 | 75:32 |
| 2010 | 4 | 236:16 |
| 2011 | 3 | 281:19 |
| 2012 | 8 | 394:00 |
| 2013 | 4 | 408:08 |
| 2014 | 4 | 481:30 |
| 2015 | 3 | 400:00 |
| 2016 | 2 | 467:00 |
| 2017 | 1 | 490:30 |
| 2018 | 1 | 442:30 |
| 2019 | 0 | 431:54 |
| 2020 | 4 | 451:00 |
| 2021 | 0 | 382:00 |
| 2022 | 0 | 317:58 |
