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          225         80 
1991          867        310 
1992          705        287 
1993         1261        470 
1994         1596        588 
1995         2714        952 
1996         2808        995 
1997         2774        948 
1998        24414      10275 
1999        13190       5037 
2000        37229      15331 
2001        42274      16636 
2002        35817      15350 
2003        58514      23954 
2004        46058      17563 
2005       308841     138959 
2006       335410     149630 
2007       195167      60433 
2008       111994      32061 
2009        92839      26067 
2010       141049      37667 
2011       149949      40964 
2012       177627      38975 
2013       234238      59262 
2014       531760     130590 
2015       757008     197434 
2016       626119     161800 
2017       525370     142879 
2018       313975      88648 
2019       822348     201207 
2020       544010     137828 
2021       738895     173192 
2022       572085     163907 
2023       522684     149672 
2024       566715     162834 
2025       548599     155066 
2026       233841      48654