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         1687        616 
1994         2354        849 
1995         4457       1538 
1996         3611       1268 
1997         2356        803 
1998        23414       9866 
1999        14718       5649 
2000        41116      17083 
2001        42264      16499 
2002        33591      14989 
2003        62815      26029 
2004        49428      18972 
2005        88804      27244 
2006       115119      36668 
2007       210674      64385 
2008       132096      37492 
2009       107680      30199 
2010       125142      34671 
2011       188455      52106 
2012       175528      48535 
2013       272627      77237 
2014       674711     172119 
2015       773014     205341 
2016       551494     148461 
2017       473641     135302 
2018       406735     114284 
2019       808432     197820 
2020       720760     185137 
2021       937488     225572 
2022       711315     203538 
2023       560136     160485