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         2351        848 
1995         4454       1537 
1996         3611       1268 
1997         2350        801 
1998        23408       9864 
1999        14710       5646 
2000        41108      17080 
2001        42240      16489 
2002        33583      14985 
2003        62787      26017 
2004        49373      18955 
2005        88723      27220 
2006       114990      36630 
2007       210467      64331 
2008       131905      37441 
2009       107471      30143 
2010       124959      34623 
2011       188246      52047 
2012       175100      48418 
2013       272360      77163 
2014       674154     171969 
2015       772462     205192 
2016       550880     148298 
2017       472924     135097 
2018       406227     114141 
2019       807689     197617 
2020       720207     184983 
2021       936674     225386 
2022       710602     203333 
2023       558095     159849