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        41118      17084 
2001        42269      16501 
2002        33595      14991 
2003        62830      26034 
2004        49429      18972 
2005        88818      27249 
2006       115150      36677 
2007       210727      64399 
2008       132130      37501 
2009       107712      30208 
2010       125159      34675 
2011       188508      52120 
2012       175651      48571 
2013       272716      77261 
2014       674824     172150 
2015       773222     205396 
2016       551671     148509 
2017       473939     135384 
2018       406921     114337 
2019       808770     197915 
2020       720943     185187 
2021       937650     225620 
2022       711660     203638 
2023       553141     158253