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          690        282 
1993         1231        460 
1994         1593        587 
1995         2714        952 
1996         2802        993 
1997         2774        948 
1998        24408      10272 
1999        13187       5036 
2000        37221      15327 
2001        42261      16630 
2002        35799      15341 
2003        58495      23945 
2004        46023      17548 
2005       308748     138918 
2006       335337     149602 
2007       195086      60411 
2008       111922      32044 
2009        92766      26048 
2010       140966      37645 
2011       149802      40924 
2012       177426      38920 
2013       234041      59207 
2014       531434     130505 
2015       756420     197283 
2016       625912     161752 
2017       525213     142834 
2018       313702      88573 
2019       821972     201159 
2020       543378     137659 
2021       737736     172912 
2022       571719     163805 
2023       522340     149579 
2024       566279     162712 
2025       548398     155038 
2026       234368      48835