March 31, 2020

Astro-Challenge: See the Galilean Moons in 1,2,3,4 Order.

Astronomy is chock full of alignments, synchronizations, and oddities that happen on variable cycles. This week, I’d like to point you towards one of those gee-whiz occurrences that happens early Friday morning. On May 28th, 2010, you’ll have the opportunity to view Jupiter’s classical four Galilean Moons in one-through-four order, all positioned on one side of the planet. This would also make for an interesting “family portrait” of the set. Jupiter is in dawn skies, currently rising about 4 hours prior to the Sun. The window of time is short; the moons are only in this arrangement from 06:33 UT until 07:50 UT, and “Jupiter-rise” for folks in the US Eastern time zone only occurs at about 0:700 UT (about 3 AM EDT local). Hence, only folks positioned in the Eastern and Atlantic time zones will have a shot at catching this alignment under dark skies.

Just how often does this event occur? Below is a listing of 1,2,3,4 alignments for the remainder of 2010 (all times are in Universal):

MAY 28 0633 TO 0750

MAY 30 2323 TO MAY 31 0331

JUN 11 1112 TO 1424

JUN 12 1512 TO 1756

JUN 25 1544 TO 1812

JUN 26 1901 TO 2225

JUL 16 2218 TO 2354

JUL 22 1052 TO 1238

JUL 31 0231 TO 0342

AUG 01 0415 TO 0916

AUG 05 1705 TO 1846

AUG 14 0636 TO 0730

AUG 15 0750 TO 1328

AUG 26 1946 TO AUG 27 0340

SEP  4 1234 TO 1312

SEP 09 2314 TO SEP 10 0929

SEP 18 1628 TO 1701

SEP 19 1633 TO 2347

SEP 24 1454 TO 1521

OCT 02 2022 TO 2032

OCT 03 2001 TO OCT 04 0359

OCT 15 0828 TO OCT 16 0033

OCT 25 0118 TO 0857

OCT 29 1224 TO OCT 30 0619

NOV 08 0454 TO 1536

NOV 22 0836 TO NOV 23 0330

DEC 04 0647 TO 1534

DEC 13 1837 TO DEC 14 0910

DEC 18 1142 TO 1925

DEC 28 0158 TO 1302

As you can see, this is nearly a weekly event. Fans of Belgian astronomer Jean Meeus will recognize this as one of his famous Mathematical Astronomy Morsels of unique pairings, alignments, and conjunctions… for example, if you want to know how often Mercury and Venus transit the Sun at the same time (a very rare event!) Meeus is your man. Our thanks to reader Ed Kotapish for running the calculations and alerting us to these unique opportunities… keep em’ coming, Ed!

But that’s not the only reason to look at the largest planet in our solar system this week. Its appearance is noticeably different as of late, due to a disappearance of one of our astro-words of the week; Equatorial Belts. One of the most noticeable surface features on Jupiter in even a small telescope is it’s broad “striped” appearance. These northern and southern equatorial belts are brownish in appearance and straddle the lighter white equatorial zone. The belts themselves are descending columns of ammonia gas that are evaporating as they fall into the warmer interior, revealing layers of darker aerosols beneath. Are aliens trying to begin fusion ignition as a tribute to the late Arthur C. Clarke? Despite what you may have read around the Net, the occasional disappearance of the Southern Equatorial Belt is not an undocumented or even singular event; in fact, this has happened a total of 17  recorded times since 1901. If the trend holds true, we’ll probably see an increase in “white spots” along the former latitude of the SEB precipitating the return of the errant belt by the end of the year.  Now is the time to catch Jupiter at an odd one-striped appearance. Conversely, the great Red Spot, which actually appears tan to salmon in color, is generally nestled in the SEB, and hence, should be easier to sight!

And Finally… notice a +6 magnitude interloper closing in on the planet? Uranus is approaching Jupiter for a close conjunction in June on the 8th…more to come!


  1. [...] This post was mentioned on Twitter by David Dickinson, Todd Barrow. Todd Barrow said: RT @Astroguyz: Astro-Challenge: See the Galilean Moons in 1,2,3,4 order. An interesting, reader submitted item w/table! [...]

  2. [...] Astro-Challenge: See the Galilean Moons in 1,2,3,4 Order. : Astro Guyz [...]

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