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        13302       5077 
2000        37417      15418 
2001        42907      16873 
2002        40064      16798 
2003        59150      24209 
2004        46319      17671 
2005       310155     139458 
2006       336493     150047 
2007       196079      60669 
2008       113454      32461 
2009        94527      26528 
2010       144660      38562 
2011       152220      41591 
2012       180171      39665 
2013       237580      60195 
2014       534201     131048 
2015       764858     199480 
2016       625217     161505 
2017       530045     144085 
2018       321651      90512 
2019       829278     202731 
2020       553342     140228 
2021       755139     177511 
2022       580585     166319 
2023       529444     151591 
2024       574696     165132 
2025       569453     162029 
2026       363041      40404