Has the conjunction between Venus, Jupiter, and Regulus only occurred twice in 2,000 years?

Question

I recently heard the claim that mid-July, the "Star of Bethlehem" formed for the first time in 2,000 years, where the Star of Bethlehem is a three-way conjunction between Venus, Jupiter, and Regulus. The Wikipedia page I just linked mentions one such conjunction occurring in 2 BC, and other sources (like EarthSky) mention the conjunction that happened last month, in 2015 AD. Has this three-way conjunction never happened in the intervening 2016 years?

(For the purpose of this question, I'll say that it counts as a conjunction when each pair of bodies is separated by no more than 10 degrees, as suggested by this CosmoQuest forum thread on the subject.)

Answer 1

The 2 BCE conjunction had Regulus, Jupiter, and Venus within 5.346 degres, and the Sun was 19.371 degrees distant.

The 2015 conjunction had the three within 5.488 degrees, with the Sun 30.930 degrees away.

There are 81 conjunctions between those two dates where Regulus, Jupiter, and Venus are less than 5.488 degrees apart, although, in some cases, the Sun would be too close to see these conjunctions.

I list all of these conjunctions below, and also include conjunctions as far back as 999 BCE and as far forward as 2999 CE.

The first two columns are the date and time.

The third column is the maximum pairwise separation (in degrees) of Regulus, Jupiter, and Venus.

The fourth column is the smallest angular distance from the Sun (in degrees) of the three.

Additional notes follow the list:

-998-08-13 17:47:22 4.460 17.341
-986-06-14 19:33:17 5.078 31.064
-962-06-13 20:42:13 1.599 37.154
-939-08-24 16:05:37 0.960 32.337
-903-06-23 23:23:31 4.166 23.499
-879-06-22 18:41:22 2.388 28.906
-856-09-02 02:38:31 0.900 40.426
-820-07-03 18:56:04 3.059 15.483
-796-07-02 11:36:42 3.326 19.880
-773-09-09 05:10:53 2.068 46.122
-737-07-14 22:02:17 1.914  7.202
-713-07-13 13:16:57 4.432 10.473
-654-07-25 04:03:45 0.919  0.676
-618-06-16 16:24:53 2.111 36.170
-571-08-04 08:00:55 0.890  9.482
-535-06-08 09:43:32 1.519 43.497
-512-08-15 20:18:35 4.304 21.310
-488-08-14 11:02:13 2.216 17.658
-452-06-14 20:40:52 1.507 38.039
-429-08-26 12:36:08 3.022 30.516
-405-08-25 05:36:22 3.500 25.655
-369-06-24 14:26:28 1.383 30.683
-346-09-04 07:24:03 2.055 38.915
-322-09-03 07:20:58 4.678 33.128
-310-07-05 12:23:59 4.755 15.643
-286-07-04 05:57:12 1.723 21.719
-263-09-10 01:35:27 1.743 44.339
-239-09-10 16:58:48 5.467 39.382
-227-07-15 14:17:13 3.299  7.717
-203-07-14 05:55:31 3.137 12.390
-156-09-12 06:11:05 5.008 41.107
-144-07-25 20:01:44 1.779  0.850
-132-06-30 22:00:27 4.887 21.625
-120-07-24 10:48:43 4.594  2.846
 -61-08-06 01:53:32 0.781  8.312
 -25-06-11 09:01:53 2.012 43.414
  -2-08-17 13:43:06 5.346 19.371 (conjunction in 2 BCE)

  -1-06-11 09:00:23 4.978 45.464
  22-08-16 03:46:55 1.066 16.885
  58-06-16 21:31:59 1.924 38.499
  81-08-27 08:28:28 4.344 28.668
  82-06-16 01:28:35 4.809 41.268
 105-08-26 00:47:42 2.203 25.078
 141-06-25 09:01:41 1.347 31.319
 164-09-05 10:04:04 3.548 37.319
 165-06-24 06:31:05 5.379 33.701
 188-09-04 07:11:50 3.049 33.055
 224-07-04 23:17:54 1.226 23.421
 247-09-13 15:10:43 3.233 44.173
 271-09-13 05:17:58 3.587 40.061
 283-07-17 06:44:26 5.353  7.568
 307-07-15 23:33:14 1.106 14.268
 330-09-10 21:05:11 4.715 41.177
 354-09-17 08:06:60 3.418 44.034
 366-07-27 11:51:60 3.985  0.992
 390-07-26 03:05:29 2.339  4.782
 449-08-06 18:09:31 2.584  6.358
 473-08-05 08:52:09 3.774  1.408
 485-06-13 23:13:34 3.793 41.669
 509-06-14 10:03:10 3.248 45.079
 532-08-16 22:56:25 1.136 15.985
 556-08-15 13:18:21 5.306  9.232
 568-06-18 04:59:43 3.729 37.949
 592-06-17 10:00:36 3.097 42.534
 615-08-27 17:07:18 0.513 24.909
 651-06-27 07:39:52 2.799 31.415
 674-09-07 10:08:57 5.021 35.627
 675-06-26 05:23:47 3.875 35.349
 698-09-06 05:27:18 1.613 32.746
 734-07-06 15:41:56 1.585 24.008
 757-09-15 06:00:16 4.344 43.078
 758-07-05 10:40:10 4.927 26.804
 781-09-14 13:11:04 2.606 39.663
 817-07-16 15:15:47 1.096 16.042
 840-09-17 11:49:26 4.635 45.023
 864-09-19 23:02:46 2.770 44.576
 876-07-28 03:47:10 5.109  0.757
 900-07-26 19:38:38 1.354  6.699
 959-08-08 09:59:38 3.685  4.399
 983-08-07 01:00:51 2.596  0.922
 995-06-18 07:09:17 4.556 40.276
1019-06-19 20:30:29 2.698 43.446
1042-08-18 14:56:17 2.469 14.017
1066-08-17 05:54:20 3.837  8.756
1078-06-20 14:43:27 5.059 37.822
1102-06-19 21:49:33 1.707 43.667
1125-08-28 15:18:36 1.383 23.486
1149-08-27 06:37:45 4.987 17.075
1161-06-28 07:08:46 4.549 31.267
1185-06-27 05:43:18 2.039 36.937
1208-09-07 05:59:08 0.502 32.528
1244-07-07 11:31:14 3.647 23.669
1268-07-06 06:22:18 2.826 28.583
1291-09-17 00:48:31 0.553 40.580
1327-07-18 07:04:40 2.460 15.742
1351-07-17 00:10:09 3.975 19.529
1374-09-23 07:58:08 1.568 46.055
1410-07-28 09:20:39 1.073  7.770
1434-07-27 02:11:36 5.317 10.122
1493-08-07 16:51:42 0.882  0.938
1529-06-29 06:47:15 2.990 37.035
1552-08-19 07:13:29 4.307 12.057
1576-08-17 22:28:03 2.198  8.457
1612-07-01 16:15:13 0.936 44.541
1635-09-09 08:38:22 2.760 21.568
1659-09-08 00:14:25 3.635 16.511
1695-07-09 07:11:03 1.123 38.488
1718-09-20 00:58:55 1.552 30.735
1742-09-18 17:58:01 4.959 24.413
1754-07-20 07:11:04 4.686 24.403
1778-07-19 02:46:21 1.812 30.338
1801-09-29 19:39:12 0.682 39.105
1837-07-31 00:36:14 3.503 16.558
1861-07-29 17:54:30 2.897 21.392
1884-10-06 07:55:46 1.204 45.253
1920-08-11 02:21:34 2.259  8.435
1944-08-09 18:40:08 4.058 12.042
2003-08-22 07:15:20 1.041  0.825

2015-07-16 11:48:33 5.488 30.930 (conjunction in 2015 CE)
2027-08-20 23:44:27 5.261  2.523
2086-09-01 14:32:37 0.790  8.374
2122-07-08 16:51:26 1.516 43.744
2145-09-14 01:53:17 4.836 19.637
2146-07-08 12:23:30 5.417 45.470
2169-09-12 17:38:23 1.559 16.679
2205-07-15 09:10:00 1.372 38.734
2228-09-24 20:25:03 3.776 28.900
2229-07-14 10:39:27 5.357 41.055
2252-09-23 13:21:48 2.792 24.725
2288-07-23 23:00:59 1.054 31.616
2311-10-05 21:49:18 2.753 37.499
2335-10-04 18:19:54 3.841 32.416
2371-08-04 11:28:25 1.029 23.258
2394-10-13 02:17:26 2.210 44.307
2418-10-12 12:48:16 4.632 38.993
2430-08-15 18:58:06 4.175  8.408
2454-08-14 11:37:59 2.188 13.939
2477-10-10 03:40:59 3.897 41.142
2501-10-16 12:47:51 4.549 41.762
2513-08-26 23:54:34 2.667  0.875
2537-08-25 15:50:58 3.690  4.447
2596-09-06 05:26:08 1.151  6.635
2620-09-05 21:40:43 5.240  0.897
2632-07-15 02:33:17 2.386 43.108
2656-07-15 11:20:55 4.650 45.236
2679-09-18 10:25:21 0.705 15.875
2715-07-21 15:26:25 2.319 39.102
2738-09-30 15:29:27 4.810 27.036
2739-07-20 18:15:52 4.425 42.356
2762-09-29 08:12:17 1.644 24.014
2798-07-29 19:09:49 1.599 32.315
2821-10-09 21:38:10 3.932 35.818
2822-07-28 16:03:44 4.946 35.075
2845-10-08 17:02:38 2.697 31.836
2881-08-08 05:45:37 0.984 24.514
2904-10-18 16:53:19 3.435 43.217
2928-10-17 21:25:11 3.325 38.965
2964-08-19 03:36:41 0.956 15.872
2987-10-21 20:20:21 4.041 45.058

Notes:

• You can (and should) check these numbers against a reliable source, such as Stellarium or HORIZONS (http://ssd.jpl.nasa.gov/?horizons)

• These numbers are imperfect for several reasons:

  • Like most planetarium programs, I neglect light travel time (Stellarium neglects light travel time by default, but you can change this in the settings). This is probably the largest error in the numbers above.

  • NASA solves differential equations from known constants to publish planetary positions. The constants aren't necessarily accurate (they are updated occasionally), and NASA publishes only approximations to the differential equations solutions. The approximations are usually good within a few meters, but if the constants were/are drastically different in the past/future (and/or are erroneous), these results would not apply.

• My methodology:

  • I used the SPICE kernels (http://naif.jpl.nasa.gov/pub/naif/toolkit_docs/C/req/kernel.html) to find the positions of Jupiter and Venus (in the ICRF J2000 frame) daily from 999 BCE to 2999 CE.

  • I assumed the position of Regulus was constant in the ICRF J2000 frame. Since ICRF J2000 is a non-precessing frame, this is essentially accurate, but neglects Regulus' small proper motion.

  • I computed the daily maximal angular separation between Jupiter, Venus, and Regulus.

  • I found local minima among the daily separations, and used the ternary method to find the instant of the actual local minimum.

  • I looked at the separations for 2 BCE and 2015 CE, and filtered the results to only show conjunctions with separations less than the maximum of these two separations.

  • I computed the position of the Sun on the filtered list, and included the separation between the Sun and the closest of the Jupiter, Regulus, and Venus.

  • I did most of the work in Mathematica, but used the Unix program j2d to convert Julian dates to calendar dates, because Mathematica uses the proleptic Gregorian calendar, which most people do not use.

  • You can see what I did (in extremely cluttered form) at:

https://github.com/barrycarter/bcapps/tree/master/ASTRO

• I wanted to present the results in a sortable HTML table, but stackexchange doesn't allow tables of any sort.

• Here are Stellarium screenshots of some of these conjunctions. Regulus is the light blue star, Venus is bright yellow, and Jupiter is the one with the moons. The object I've selected (if any) is not necessarily relevant to the conjunction.

Answer 2

Though my computer is still crunching the numbers (and subsequently slowing everything else down... ) I can tell you the answer is no. It's up to the 1700s already (starting from 2 BC) and I've already seen multiple conjunctions in quite decent proximity of all three. I set the max to 5 degrees. I'm using a modified form of this python script. http://shallowsky.com/blog/science/astro/predicting-conjunctions.html

Ok, the script has finished. I don't have it nicely filtered down to ONLY the conjunctions of all three, so I have 3000+ lines of results. I can copy a few instances in real quick though.

Conjunction of Venus, Jupiter and Regulus lasts from 2015/6/23 to 2015/8/4.
Venus and Jupiter are closest on 2015/7/2 (0.4 deg).
Venus and Regulus are closest on 2015/7/16 (2.4 deg).
Jupiter and Regulus are closest on 2015/8/4 (1.8 deg).

Conjunction of Venus, Regulus and Jupiter lasts from 1885/7/25 to 1885/8/11.
Venus and Regulus are closest on 1885/7/29 (1.1 deg).
Venus and Jupiter are closest on 1885/8/7 (0.4 deg).

Conjunction of Jupiter, Regulus and Venus lasts from 1861/6/19 to 1861/8/6.
Jupiter and Regulus are closest on 1861/7/16 (0.5 deg).
Regulus and Venus are closest on 1861/7/30 (1.1 deg).
Jupiter and Venus are closest on 1861/8/2 (0.6 deg).

Conjunction of Venus, Jupiter and Regulus lasts from 1837/7/24 to 1837/8/3.
Venus and Jupiter are closest on 1837/7/28 (0.7 deg).
Venus and Regulus are closest on 1837/7/31 (1.2 deg).
Jupiter and Regulus are closest on 1837/7/31 (3.6 deg).

Conjunction of Venus, Regulus and Jupiter lasts from 1802/7/16 to 1802/8/1.
Venus and Regulus are closest on 1802/7/19 (1.1 deg).
Venus and Jupiter are closest on 1802/7/27 (0.5 deg).

Conjunction of Jupiter, Regulus and Venus lasts from 1778/6/12 to 1778/8/2.
Jupiter and Regulus are closest on 1778/7/11 (0.5 deg).
Regulus and Venus are closest on 1778/7/19 (1.2 deg).
Jupiter and Venus are closest on 1778/7/21 (0.6 deg).

Conjunction of Venus, Jupiter and Regulus lasts from 1754/7/12 to 1754/7/31.
Venus and Jupiter are closest on 1754/7/16 (0.8 deg).
Venus and Regulus are closest on 1754/7/21 (1.2 deg).
Jupiter and Regulus are closest on 1754/7/31 (2.5 deg).

You should probably verify these finds with a program like Stellerium. Note that I set the view point to be in the middle east. Roughly where Persia used to be.