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         2808        995 
1997         2774        948 
1998        24412      10274 
1999        13187       5036 
2000        37221      15327 
2001        42266      16632 
2002        35801      15342 
2003        58501      23948 
2004        46032      17552 
2005       308798     138940 
2006       335349     149606 
2007       195112      60418 
2008       111922      32044 
2009        92781      26052 
2010       140977      37648 
2011       149839      40934 
2012       177448      38926 
2013       234102      59223 
2014       531462     130513 
2015       756427     197283 
2016       625915     161750 
2017       525081     142798 
2018       313753      88587 
2019       821801     201104 
2020       543430     137674 
2021       737804     172932 
2022       571766     163818 
2023       522373     149588 
2024       566316     162721 
2025       548430     155046 
2026       233437      48589