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         1258        469 
1994         1596        588 
1995         2714        952 
1996         2808        995 
1997         2774        948 
1998        24414      10275 
1999        13190       5037 
2000        37227      15330 
2001        42268      16633 
2002        35811      15347 
2003        58505      23950 
2004        46042      17556 
2005       308822     138950 
2006       335380     149619 
2007       195120      60420 
2008       111937      32048 
2009        92797      26056 
2010       140988      37651 
2011       149866      40941 
2012       177480      38935 
2013       234153      59238 
2014       531532     130530 
2015       756503     197303 
2016       625945     161755 
2017       525169     142821 
2018       313799      88599 
2019       821809     201101 
2020       543585     137717 
2021       738011     172985 
2022       571826     163835 
2023       522439     149607 
2024       566428     162752 
2025       548523     155050 
2026       233425      48587