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         2807        983 
1996         2823       1000 
1997         2804        958 
1998        24475      10297 
1999        13290       5072 
2000        37386      15403 
2001        42878      16860 
2002        40024      16779 
2003        59434      24303 
2004        46333      17673 
2005       309899     139350 
2006       336220     149936 
2007       196065      60673 
2008       113174      32386 
2009        94272      26457 
2010       144676      38561 
2011       151906      41498 
2012       179632      39517 
2013       236936      60012 
2014       533573     130874 
2015       763014     198992 
2016       625834     161701 
2017       528838     143755 
2018       320592      90206 
2019       828035     202380 
2020       551136     139602 
2021       751743     176612 
2022       579224     165931 
2023       527949     151168 
2024       573551     164805 
2025       560709     159244 
2026       244162      41795