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         1681        614 
1994         2354        849 
1995         4454       1537 
1996         3611       1268 
1997         2356        803 
1998        23411       9865 
1999        14715       5648 
2000        41116      17083 
2001        42249      16493 
2002        33589      14988 
2003        62804      26024 
2004        49402      18963 
2005        88749      27228 
2006       115040      36645 
2007       210526      64346 
2008       131954      37454 
2009       107509      30153 
2010       125020      34639 
2011       188346      52076 
2012       175187      48441 
2013       272449      77188 
2014       674331     172017 
2015       772679     205248 
2016       551066     148345 
2017       473090     135141 
2018       406342     114173 
2019       807911     197675 
2020       720370     185029 
2021       936910     225435 
2022       710742     203371 
2023       558559     160035