Year Observations     Objects
1858            3          3 
1889            1          1 
1901            1          1 
1920            6          2 
1950            2          1 
1951            6          3 
1953           14          8 
1954           12          5 
1955           14          7 
1956            8          4 
1960            6          3 
1974            2          1 
1975            2          1 
1976            8          4 
1977            2          1 
1978           12          5 
1981           18          5 
1982           13          7 
1983            8          4 
1984            2          1 
1985            8          4 
1986            4          2 
1987            2          1 
1988           38         18 
1990          219         78 
1991          864        309 
1992          702        286 
1993         1246        465 
1994         1596        588 
1995         2714        952 
1996         2802        993 
1997         2774        948 
1998        24412      10274 
1999        13187       5036 
2000        37221      15327 
2001        42264      16631 
2002        35799      15341 
2003        58499      23947 
2004        46028      17550 
2005       308770     138928 
2006       335349     149606 
2007       195098      60414 
2008       111922      32044 
2009        92777      26051 
2010       140973      37647 
2011       149826      40930 
2012       177433      38922 
2013       234083      59218 
2014       531461     130512 
2015       756410     197279 
2016       625892     161744 
2017       525074     142795 
2018       313730      88581 
2019       821826     201112 
2020       543410     137668 
2021       737763     172920 
2022       571744     163812 
2023       522348     149581 
2024       566294     162715 
2025       548425     155044 
2026       233427      48586