Well...I don't have an accurate ephemeris on hand for the 19th and 20th centuries that gives the ecliptic longitudes of the Sun and planets, but I can tell you from Bryant Tuckerman's book Planetary, Lunar and Solar Positions for 1 AD to 1649 AD, that on July 25, 1624 there was an 'alignment' of Jupiter, Saturn, Mars, Sun, Mercury, Venus where the distance from the Sun to Jupiter in the evening sky was only 22 degrees, and from Venus to the Sun in the morning sky, the distance was 13 degrees, with the other planets in between. This alignment was almost as tight as the May 5, 2000 event, and I found this one only 25 years from the end of Tuckerman's tabulations so these types of alignments are rather common. I estimate perhaps 1 - 2 per century.
I just had a look at the US Nautical Almanac for the period from 1996 to 1954, and they have a Planetary Visibility plot near the front of the book which shows the locations of the planets each day relative to the Sun. From these plots it was easy to spot when interesting Grand Conjunctions happened. I found several that looked at least as good as what is forecast for May 5, 2000. I list the more spectacular ones below which had bright planets within about 45 degrees of the Sun. Below the symbols are S = saturn, J = jupiter, M = mars, V = venus, m = mercury, * = sun. Planets to the left of the Sun are evening objects, and to the right are morning objects:
Date planet lineup ------------------------------------------------------------ Jan 15, 1960 * S M J V March 1, 1962 V * J M m S Dec 10, 1970 m * J V M Aug 31, 1976 M V m * S Sep 10, 1981 (S J) V m * M Dec 20, 1984 M V J m * S
The Sky and Telescope monthly calendar says that in January 1960, Saturn and Mars were in conjunction with Mars ( 1.5 degrees apart) and Jupiter and Venus were in conjunction, and on the 25th, the crescent Moon was also in the picture. In 1962, the waning crescent moon occulted mercury, Mars was too close to the sun for easy observing, as was Jupiter. Saturn rose about 2 hours before the sun. This was a very tight Grand Conjunction, but its visibility was poor because the planets were 'lines up' too close to the sun most of March. The most spectacular Grand Conjunction seems to have been on September 10, 1984 when the 4 planets in the evening sky were lined up within 16 degrees of the Sun! Saturn and Jupiter were also in conjunction with each other with a 4 degree separation. There was a more recent Grand Conjunction on December, 20 1984 with a somewhat wider separation of about 40 degrees between Mercury and Mars. Jupiter and Venus were in conjunction with each other in November 1984.
So you see, in 1981 we had a Grand Conjunction nearly as good as the May 5, 2000 event, and as I said before, these things seem to happen about 1-2 times every century.
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