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        23397       9859 
1999        14688       5637 
2000        41029      17043 
2001        42157      16459 
2002        33508      14953 
2003        62660      25967 
2004        49307      18928 
2005        88490      27152 
2006       114640      36533 
2007       209940      64190 
2008       131470      37322 
2009       107050      30030 
2010       124389      34471 
2011       187676      51891 
2012       174115      48150 
2013       271431      76909 
2014       672362     171494 
2015       770511     204669 
2016       564780     151723 
2017       519915     146025 
2018       413051     115961 
2019       904040     220936 
2020       727307     186824 
2021       935025     225047 
2022       708970     202865 
2023       604659     174027