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          219         78 
1991          864        309 
1992          699        285 
1993         1237        462 
1994         1596        588 
1995         2714        952 
1996         2802        993 
1997         2774        948 
1998        24408      10272 
1999        13187       5036 
2000        37221      15327 
2001        42264      16631 
2002        35799      15341 
2003        58495      23945 
2004        46023      17548 
2005       308748     138918 
2006       335341     149604 
2007       195090      60412 
2008       111922      32044 
2009        92773      26050 
2010       140970      37646 
2011       149802      40924 
2012       177426      38920 
2013       234045      59208 
2014       531434     130505 
2015       756428     197285 
2016       625917     161753 
2017       525179     142825 
2018       313712      88576 
2019       821931     201146 
2020       543381     137660 
2021       737740     172913 
2022       571727     163807 
2023       522340     149579 
2024       566287     162713 
2025       548402     155039 
2026       234405      48847