# See end of file for documentation YYYY MM DD Lon Source/comments 3022 11 1 24386 (extrapolation: 24 deg/yr over 1000 yr = 24000 deg; see comments) 2022 11 1 386 (2010-present from http://jupos.privat.t-online.de/rGrs.htm) 2022 5 1 374 2021 12 1 365 2021 9 1 362 2021 4 1 357 2020 12 1 347 2020 8 1 339 2020 4 1 330 2019 11 1 320 2019 9 1 315 2019 7 1 313 2019 5 1 309 2019 1 1 300 2018 11 1 296 2018 6 1 288 2018 4 1 288 seems to be a (temporary?) 'halt' in Apr/May 2018 2017 10 1 280 2017 08 1 276 2016 12 1 258 2016 9 1 253 2016 4 1 244 2015 12 1 236 2015 5 1 227 2015 1 1 226 2014 9 1 216 2014 4 1 212 2014 2 1 209 2013 10 1 202 2012 8 1 182 2012 1 1 174 2011 8 1 168 2011 2 1 163 2010 10 10 156 2009 7 15 138 (From Sky & Tel Web site) 2008 7 15 127 (From Sky & Tel Web site) 2008 3 1 121 (Mar 2008 Christopher Go value) 2007 5 1 114 (Jul 2007 S&T) 2006 6 1 109 (Aug 2006 S&T) 2006 3 1 104 (May 2006 S&T) 2005 3 1 98 (May 2005 S&T) 2005 1 1 98 (Mar 2005 S&T) 2004 12 1 94 (Feb 2005 S&T) 2004 11 1 94 (Jan 2005 S&T) 2004 10 1 94 (Dec 2004 S&T) 2003 11 1 84 (Jan 2004) 2003 9 1 84 (Nov 2003) 2003 1 1 80 (Mar 2003) 2002 3 1 80 (May 2002) 2002 2 1 80 (Apr 2002) 2002 1 1 77 (Mar 2002) 2001 12 1 77 (Feb 2002) 2001 11 1 77 (Jan 2002) 2001 10 1 77 (Dec 2001 S&T) 2001 9 1 76 (Nov 2001 S&T) 2001 8 1 76 (Oct 2001 S&T) 2001 5 1 76 (Aug 2001 S&T) 2001 3 1 76 (May 2001 S&T) 2001 2 1 76 (Apr 2001 S&T) 2001 1 1 76 (Mar 2001 S&T) 2000 12 1 76 (Feb 2001 S&T) 2000 11 1 76 (Jan 2001 S&T) 2000 10 1 74 (Dec 2000) 1999 12 1 66 (Jan 2000) 1998 11 1 64 (Jan 1999) 1997 5 1 62 (July, 1997) 1996 9 1 61 (November, 1996) 1996 8 1 51 (Oct 1996) 1996 7 1 51 (September, 1996) 1995 9 1 49 (November, 1995) 1995 6 1 42 (Aug 1995) 1995 5 1 42 (July, 1995) 1994 6 1 40 (Aug 1994) 1994 5 1 41 (July, 1994) 1994 4 1 40 (June, 1994) 1993 5 1 45 (Jul 1993) 1993 2 1 38 1992 7 1 33 1992 6 1 33 1992 5 1 30 1992 4 1 30 1992 3 1 34 1992 2 1 34 1991 6 1 32 1991 5 1 32 1991 4 1 32 1991 3 1 27 1991 2 1 27 1991 1 1 27 1990 12 1 27 1990 4 1 22 1990 3 1 22 1990 2 1 22 1990 1 1 30 1989 11 1 30 1989 2 1 16 1989 1 1 16 1988 12 1 16 1988 11 1 16 1988 1 1 14 1987 12 1 14 1987 11 1 14 1986 11 1 19 1986 10 1 19 1986 7 1 19 http://jupos.privat.t-online.de/img/oRS19b.gif 1984 6 1 28 http://jupos.privat.t-online.de/img/oRS19b.gif 1983 7 27 39 http://jupos.privat.t-online.de/img/oRS19b.gif 1982 5 2 51 http://jupos.privat.t-online.de/img/oRS19b.gif 1982 1 1 54 http://jupos.privat.t-online.de/img/oRS19b.gif 1980 12 6 53 http://jupos.privat.t-online.de/img/oRS19b.gif 1980 5 13 58 http://jupos.privat.t-online.de/img/oRS19b.gif 1980 1 12 56 http://jupos.privat.t-online.de/img/oRS19b.gif 1979 10 21 61 http://jupos.privat.t-online.de/img/oRS19b.gif 1978 9 26 57 http://jupos.privat.t-online.de/img/oRS19b.gif 1978 4 14 55 http://jupos.privat.t-online.de/img/oRS19b.gif 1977 2 9 48 http://jupos.privat.t-online.de/img/oRS19b.gif 1976 10 7 41 http://jupos.privat.t-online.de/img/oRS19b.gif 1976 3 15 49 http://jupos.privat.t-online.de/img/oRS19b.gif 1975 11 13 45 http://jupos.privat.t-online.de/img/oRS19b.gif 1975 6 21 35 http://jupos.privat.t-online.de/img/oRS19b.gif 1975 1 30 29 http://jupos.privat.t-online.de/img/oRS19b.gif 1974 11 9 21 http://jupos.privat.t-online.de/img/oRS19b.gif 1974 5 27 14 http://jupos.privat.t-online.de/img/oRS19b.gif 1973 10 14 7 http://jupos.privat.t-online.de/img/oRS19b.gif 1972 8 29 0 http://jupos.privat.t-online.de/img/oRS19b.gif 1972 6 8 -1 http://jupos.privat.t-online.de/img/oRS19b.gif 1971 9 15 7 http://jupos.privat.t-online.de/img/oRS19b.gif 1971 2 2 11 http://jupos.privat.t-online.de/img/oRS19b.gif 1971 1 12 16 http://jupos.privat.t-online.de/img/oRS19b.gif 1970 7 30 22 http://jupos.privat.t-online.de/img/oRS19b.gif 1970 4 19 19 http://jupos.privat.t-online.de/img/oRS19b.gif 1969 7 25 24 http://jupos.privat.t-online.de/img/oRS19b.gif 1969 5 4 21 http://jupos.privat.t-online.de/img/oRS19b.gif 1968 6 10 21 http://jupos.privat.t-online.de/img/oRS19b.gif 1968 2 29 27 http://jupos.privat.t-online.de/img/oRS19b.gif 1967 3 15 28 http://jupos.privat.t-online.de/img/oRS19b.gif 1966 1 10 22 http://jupos.privat.t-online.de/img/oRS19b.gif 1965 3 6 21 http://jupos.privat.t-online.de/img/oRS19b.gif 1964 11 4 17 http://jupos.privat.t-online.de/img/oRS19b.gif 1964 9 24 18 http://jupos.privat.t-online.de/img/oRS19b.gif 1962 12 31 17 1965MNRAS.130..423P (eyeballed on graph) 1962 8 31 14 1965MNRAS.130..423P (eyeballed on graph) 1957 04 13 -52 From JUPOS database : single observation by Voigt 1952 11 10 -89 Bertrand Peek: The Planet Jupiter (see notes) 1951 10 7 -104 1950 9 3 -110 1949 7 30 -119 1948 6 27 -126 1947 5 24 -130 1946 4 21 -143 1945 3 18 -148 1944 2 14 -177 1943 1 11 -188 1941 12 8 -191 1940 11 5 -187 1939 10 2 -194 1938 8 29 -213 1937 7 26 -221 1936 6 22 -218 1935 5 19 -201 1934 4 16 -180 1933 3 13 -157 1932 2 10 -131 1931 1 7 -103 1929 12 3 -76 1928 10 30 -45 1927 9 27 -16 1926 8 24 21 1925 7 21 90 1924 6 18 172 1923 5 14 230 1922 4 11 256 1921 3 8 284 1920 2 5 322 1919 1 2 370 1917 11 29 439 1916 10 25 490 1915 9 22 533 1914 8 19 564 1913 7 16 621 1912 6 13 664 1911 5 10 688 1910 4 6 728 1909 3 3 737 1908 1 30 743 1906 12 27 738 1905 11 24 748 1904 10 21 745 1903 9 18 754 1902 8 14 762 1901 7 11 766 1900 6 8 760 1899 5 5 751 1898 4 2 742 1897 2 29 735 1896 1 25 727 1894 12 22 720 1893 11 19 718 1892 10 16 716 1891 9 13 714 1889 7 6 714 1887 4 30 733 1884 1 21 755 1880 10 11 848 1878 8 5 976 1876 5 28 1117 1873 2 19 1304 1869 11 10 1485 1867 9 3 1607 1864 5 24 1782 1863 4 21 1849 1860 1 11 1996 1858 12 8 2014 1857 11 5 2046 1856 10 2 2075 1855 8 28 2109 1852 5 19 2246 1851 4 16 2297 1850 3 13 2345 1845 10 30 2549 1840 5 14 2816 1832 9 22 3220 1831 8 19 3308 End Comments can be added freely after the above 'End' line. At one point, the GRS longitude in Guide was set by the user. But the GRS moves; what is really needed is a table giving the GRS longitude as a function of time. This file provides that table. Guide computes the System II GRS longitude for any date by interpolating within this table. Data are given from most recent to oldest. For each date, a year, month, day, and System II longitude are given, followed by the source of the data. For dates after the most recent data point, the last GRS longitude is used; for dates preceding the table, the oldest GRS longitude is used. Note that, while coverage is good for years since 1986, the data gets a little sparser for previous dates. As of September 2017, the GRS longitude appears to be increasing at about 24 degrees per year (with plenty of fluctuations). I've taken the most recent data point, added a thousand years and 24000 degrees to it, and added it as an extrapolated value. This is just to get around the fact that otherwise, the GRS would remain at the last listed value, which is almost certainly even less realistic than the assumed drift. (Previous versions of this file used different drift rates.) Data since 2009 has come from JUPOS, the database for object positions on Jupiter. 1986 to 2009 longitudes came from _Sky & Telescope_, which in turn got the data from ALPO (Association of Lunar and Planetary Observers). I checked a random sampling of my back issues of that magazine to compile the table. Because S&T is published about two months before the date given on the cover, I've assumed that the longitude given in (for example) the August issue of a given year is the one that was actually measured in June, and have arbitrarily chosen the first of the month. Data from 1964 to 1987 came from http://jupos.privat.t-online.de/img/oRS19b.gif I was able to measure pixel positions in PaintShop Pro and write a little code to convert (pix_x, pix_y) to year and GRS longitude, so these will be at least passably accurate. Getting the underlying data would be even better, of course, but I've had no luck on that yet. Jari Suomela found some data in Bertrand Peek's book _The Planet Jupiter_ for years 1831 to 1952. See 'grs_peek.cpp' for details. Other sources would be welcome. I had hopes of going back before 1831, but this is unlikely; the GRS may have been first observed in that year, by Samuel Heinrich Schwabe. It seems likely that Robert Hooke observed it in 1664 and Cassini (as a "permanent spot") between 1665 and 1713 : http://articles.adsabs.harvard.edu//full/1987JBAA...97..215F/0000218.000.html If it were possible to figure out a passably exact GRS longitude from these data, however, we'd still have trouble filling in the gap between 1713 and 1831. You'll also notice a gap between Peek's data (which ends in 1952) and the 'jupos' image, which only goes back to 1964. It should be possible to fill that gap. 17 June 2006 version: created by BJG 6 June 2007: updated with new data and 2017 "observation" added 9 Mar 2008: added 1968 and earlier data from Peek via Jari Suomela; see 'grs_peek.cpp' for details 21 Sep 2009: added GRS longitude for August 2009 from S&T site. 15 Oct 2010: added GRS longitude from jupos.org 2013 Oct 6: added another GRS longitude from jupos.org, corrected the extrapolated value 2013 Oct 8: added 1964-1986 data from jupos.org 2013 Oct 12: revised section about pre-1831 observations after comments from Jari Suomela