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         1261        470 
1994         1607        592 
1995         2807        983 
1996         2817        998 
1997         2801        957 
1998        24468      10295 
1999        13290       5072 
2000        37357      15390 
2001        42848      16846 
2002        40001      16768 
2003        59381      24279 
2004        46289      17655 
2005       309775     139304 
2006       336112     149897 
2007       195930      60637 
2008       113022      32343 
2009        94069      26404 
2010       144400      38489 
2011       151586      41412 
2012       179299      39428 
2013       236578      59912 
2014       533572     130912 
2015       761885     198688 
2016       626016     161755 
2017       528023     143549 
2018       319895      90011 
2019       827158     202141 
2020       549193     139087 
2021       749912     176093 
2022       578436     165706 
2023       527121     150936 
2024       572471     164490 
2025       557357     158207 
2026       244897      41971