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         2348        847 
1995         4451       1536 
1996         3608       1267 
1997         2347        800 
1998        23392       9857 
1999        14688       5637 
2000        41029      17043 
2001        42154      16458 
2002        33508      14953 
2003        62660      25967 
2004        49304      18927 
2005        88488      27151 
2006       114622      36528 
2007       209936      64189 
2008       131451      37317 
2009       107035      30026 
2010       124367      34465 
2011       187649      51884 
2012       174094      48144 
2013       271357      76890 
2014       672330     171486 
2015       770439     204650 
2016       564732     151709 
2017       519877     146015 
2018       412970     115938 
2019       903859     220885 
2020       727272     186814 
2021       934961     225030 
2022       708932     202854 
2023       604608     174013