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          228         81 
1991          867        310 
1992          716        291 
1993         1264        471 
1994         1607        592 
1995         2813        985 
1996         2823       1000 
1997         2813        961 
1998        24481      10299 
1999        13316       5082 
2000        37438      15428 
2001        42922      16880 
2002        40090      16809 
2003        59186      24223 
2004        46348      17682 
2005       310320     139523 
2006       336669     150115 
2007       196174      60695 
2008       113648      32513 
2009        94792      26603 
2010       144817      38604 
2011       152469      41659 
2012       180462      39744 
2013       238039      60324 
2014       532830     130716 
2015       764112     199275 
2016       617999     159530 
2017       530412     144177 
2018       322279      90702 
2019       829659     202834 
2020       553807     140329 
2021       756215     177806 
2022       581522     166589 
2023       530209     151808 
2024       575458     165352 
2025       570717     162186 
2026       129968      34331