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          713        290 
1993         1264        471 
1994         1607        592 
1995         2810        984 
1996         2823       1000 
1997         2804        958 
1998        24481      10299 
1999        13299       5076 
2000        37417      15418 
2001        42907      16873 
2002        40062      16797 
2003        59142      24206 
2004        46319      17671 
2005       310146     139454 
2006       336476     150040 
2007       196075      60668 
2008       113431      32455 
2009        94499      26520 
2010       144656      38562 
2011       152206      41587 
2012       180145      39658 
2013       237533      60182 
2014       534813     131189 
2015       764701     199438 
2016       625629     161629 
2017       530081     144097 
2018       321610      90501 
2019       829230     202718 
2020       553264     140206 
2021       754978     177466 
2022       580472     166286 
2023       529266     151541 
2024       574502     165078 
2025       569385     162016 
2026       236679      39710