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          535        201 
1992          936        367 
1993         1690        617 
1994         2360        851 
1995         4493       1550 
1996         3611       1268 
1997         2356        803 
1998        23428       9871 
1999        14732       5655 
2000        41155      17101 
2001        42296      16512 
2002        33614      15000 
2003        62887      26057 
2004        49478      18989 
2005        88938      27285 
2006       115306      36721 
2007       210921      64451 
2008       132433      37583 
2009       107981      30280 
2010       125452      34753 
2011       188923      52231 
2012       176024      48672 
2013       273187      77391 
2014       675348     172288 
2015       773956     205594 
2016       552285     148680 
2017       474428     135524 
2018       407249     114430 
2019       809111     198006 
2020       721226     185266 
2021       937911     225694 
2022       712003     203740 
2023       547861     156699