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         1604        591 
1995         2804        982 
1996         2814        997 
1997         2789        953 
1998        24450      10289 
1999        13274       5066 
2000        37295      15362 
2001        42776      16815 
2002        39912      16734 
2003        59190      24198 
2004        46178      17610 
2005       309385     139158 
2006       335772     149768 
2007       195616      60554 
2008       112546      32213 
2009        93498      26249 
2010       141692      37835 
2011       150897      41223 
2012       178580      39230 
2013       235480      59608 
2014       533598     131057 
2015       760364     198339 
2016       626985     162038 
2017       526865     143265 
2018       317957      89524 
2019       825700     201818 
2020       546430     138416 
2021       745356     174840 
2022       575555     164889 
2023       525050     150340 
2024       569781     163716 
2025       554090     156844 
2026       221577      44876