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        13294       5074 
2000        37398      15409 
2001        42883      16862 
2002        40035      16784 
2003        59464      24313 
2004        46356      17680 
2005       309968     139376 
2006       336288     149957 
2007       196104      60683 
2008       113271      32412 
2009        94350      26478 
2010       144795      38592 
2011       152116      41555 
2012       179797      39563 
2013       237209      60091 
2014       534102     131008 
2015       763698     199171 
2016       625866     161707 
2017       529302     143882 
2018       321044      90336 
2019       828507     202515 
2020       552024     139854 
2021       753319     177050 
2022       579710     166070 
2023       528408     151299 
2024       574188     164989 
2025       565527     160768 
2026       243741      41666