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          699        285 
1993         1246        465 
1994         1596        588 
1995         2714        952 
1996         2802        993 
1997         2774        948 
1998        24408      10272 
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       195090      60412 
2008       111922      32044 
2009        92777      26051 
2010       140973      37647 
2011       149814      40927 
2012       177433      38922 
2013       234079      59217 
2014       531454     130510 
2015       756439     197288 
2016       625891     161744 
2017       525112     142805 
2018       313726      88580 
2019       821852     201120 
2020       543394     137664 
2021       737759     172919 
2022       571744     163812 
2023       522344     149580 
2024       566294     162715 
2025       548421     155043 
2026       233456      48592