On April 3 and 4, 2020, the planet Venus moves through the Pleiades open cluster (M45) in the constellation the Bull. How often does that happen?

I calculated for the period between the years −4712 and +3501 when Venus passed at less than 1 degree from the center of the Pleiades, with that center chosen at right ascension 56.75° and declination +24.17° (J2000.0).

The most recent and upcoming cases are listed in the following table:

Table 1: Least Distance Venus - Pleiades 1841 - 2223

Date Distance/°
1841-05-09.0 0.18
1980-04-03.5 0.97
1988-04-03.5 0.86
1996-04-03.5 0.74
2004-04-03.6 0.62
2012-04-03.8 0.48
2020-04-03.9 0.34
2028-04-04.2 0.20
2036-04-04.6 0.02
2044-04-05.0 0.16
2052-04-05.6 0.33
2060-04-06.4 0.55
2068-04-07.3 0.78
2076-05-14.1 0.47
2084-05-08.2 0.49
2223-04-07.8 0.92

So between 1980 and 2084, Venus passes through the Pleiades (at less than 1° from the center) once every 8 years, and before and after that does not pass through the Pleiades for about 140 years. The middle of the current active period, when Venus comes closest to the center, is in 2036.

Fig. 1: Least Distance Venus - Pleiades 1600 - 2400

This pattern repeats itself, as can be seen in Figure 1. The centers of successive active periods are about 240 years apart. The centers of the nearest active periods are in 1323, 1558, 1801, 2036, 2279, 2514, 2757, with 235 or 243 years in between.

Those periods of 8, 235, and 243 years occur because those are, with only very small errors, multiples of the orbital period of the Earth and at the same time multiples of the orbital period of Venus, so after that much time the Earth and Venus are in nearly the same relative positions, and Venus is in nearly the same direction as seen from Earth.

Of the other planets, only Mercury passed through the Pleiades, but not anymore after the year −266. The other planets come in the neighborhood of the Pleiades but not close enough. Their least distances are shown in the following table.

Table 2: Least Distance to the Pleiades, years −4712 - 3501

Planet Distance/°
Mars 1.32
Jupiter 4.70
Saturn 5.82
Uranus 4.26
Neptune 5.74

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Last updated: 2020-04-01