Year Observations     Objects
1950            2          1 
1951            6          3 
1953            4          2 
1954            2          1 
1955            4          2 
1956            2          1 
1960            6          3 
1974            2          1 
1975            2          1 
1976            8          4 
1977            2          1 
1978            8          3 
1981            4          2 
1982           12          6 
1983            8          4 
1984            2          1 
1985            8          4 
1986            4          2 
1987            2          1 
1988           38         18 
1990           32         14 
1991          532        200 
1992          936        367 
1993         1678        613 
1994         2342        845 
1995         4451       1536 
1996         3608       1267 
1997         2344        799 
1998        23380       9854 
1999        14677       5632 
2000        40995      17028 
2001        42113      16443 
2002        33461      14933 
2003        62618      25949 
2004        49262      18911 
2005        88355      27110 
2006       114433      36475 
2007       209764      64142 
2008       131237      37260 
2009       106845      29974 
2010       124058      34384 
2011       187387      51812 
2012       173657      48023 
2013       270970      76783 
2014       671814     171351 
2015       769822     204488 
2016       564442     151626 
2017       521707     146275 
2018       412577     115826 
2019       905461     221228 
2020       726529     186616 
2021       934377     224880 
2022       708224     202652 
2023       603884     173741