Mutual Event Season Heats Up at Jupiter

Europa eclipses then occults Io
In this 11.4-minute sequence taken with a 14-inch Schmidt-Cassegrain telescope, Europa first occults after which partially eclipses Io on February 7, 2015, over the past mutual occasions season. Here’s the animated version.
John Sussenbach

After their spectacular Great Conjunction final December, Jupiter and Saturn overwintered within the solar glare, misplaced from sight. They’ve now returned to the morning sky to start one other observing season, and amateurs are looking forward to a glance.

Jupiter and Saturn return at dawn
Both Jupiter and Saturn are actually simply seen low within the southeastern sky at daybreak.
Bob King

Unlike some planets that maintain their particulars shut, Jupiter lets all of it hang around. With an obvious diameter practically double that of Mars at its closest opposition even a modest telescope reveals a colourful cloudscape of shifting belts and zones. The 4 Galilean moons are continually on the transfer, bunching collectively and spreading aside like ballet dancers within the Nutcracker. If that wasn’t sufficient, you possibly can watch the planet occult and eclipse these satellites or catch a transit, when a moon casts its pinpoint shadow on the gas big’s cloud tops.

The Feeling Is Mutual

But there’s one thing else occurring that makes this Jupiter apparition particular. Every six years the orbital plane of the 4 Galilean moons is edge-on with the Sun and Earth, and we enter the season of mutual phenomena, when the moons occult and eclipse each other. The season started on January third when Europa partially eclipsed Io and finally ends up on November sixteenth with a Ganymede-Io occultation. Although Jupiter remains to be low at daybreak it inches greater each morning and can quickly be in good view.

Io and Ganymede dance
Io and its shadow overtake bigger Ganymede on this 14-image sequence taken each jiffy from 16:38 to 17:39 Universal Time on August 16, 2009. Christopher Go

In whole 242 occasions happen, of which 192 are observable. An occultation occurs when one moon passes in entrance of one other, blocking a portion of the background moon’s disk. During an eclipse a foreground moon casts its shadow on a background moon. Occultations could be partial or whole, whereas eclipses are partial, whole, or annular.

Mutual Event Types
Mutual satellite tv for pc occasions can happen in any of six methods, relying on slight variations within the moons’ angular sizes and relative positions.
Sky & Telescope

Depending on the character of the occultation occasion, the 2 moons might seem to barely contact and even fully merge. When closest, the spacing and orientation of the 2 moons adjustments quickly, an thrilling sight you possibly can see unfold in near-real time. Magnitude variations between the satellites additionally make for noticeable brightness adjustments throughout an occultation. This is particularly true for Jupiter’s opposition on August twentieth, when the dimmest of the Galilean moons, 5.5-magnitude Callisto absolutely occults 4.4-magnitude Ganymede, leading to a dramatic drop in brightness. Similar circumstances happen with Io (magnitude 4.9) and to a lesser extent with Europa (magnitude 5.1).

Io eclipses Ganymede
Io eclipses Ganymede on March 13, 2015, as seen photographed by way of a 14-inch Schmidt-Cassegrain telescope.
John Sussenbach

In an eclipse, the dip in brightness varies in keeping with the depth of the eclipse. During a complete eclipse a moon might briefly disappear from view in a multi-magnitude plunge. I’ve included a selective desk beneath, however you possibly can peruse a listing of all occasions at the Institute of Celestial Mechanics and Ephemeris Computing (IMCCE) site.

Jupiter's Ganymede occults then eclipses Io
Ganymede occults after which eclipses Io on February 9, 2015.
Marc Delcroix

Table of Portents

Date Time (UT) Event Mag. (%)
April 1 13:17 — 13:23 Ganymede occults Io 94
April 6 11:46 — 11:51 Europa eclipses Io 47
April 11 10:00 — 10:11 Io eclipses Callisto 69
April 12 11:50 — 12:12 Io eclipses Callisto 80
April 15 10:07 — 10:16 Ganymede eclipses Europa 95
April 18 9:52 — 9:57 Io eclipses Europa 87
April 22 13:23 — 13:32 Ganymede eclipses Europa 81
April 25 12:05 — 12:11 Io eclipses Europa 98
April 29 12:12 — 12:27 Ganymede eclipses Callisto 75
This desk highlights occasions seen from the Americas in April 2021. Maximum occultation or eclipse happens at the center of the time interval. The magnitude of an occasion is the proportion of the extra distant satellite tv for pc’s diameter that’s coated in an occultation or obscured throughout an eclipse. The better the quantity the extra dramatic the sunshine change in an eclipse and the extra central the occultation. 50 p.c or extra needs to be simply seen.

To use the IMCCE web site, click on the Show button for the whole record of occasions. Times for the start and finish of the occasion are in Universal Time, so keep in mind to deduct 4 hours for Eastern Daylight; 5 for Central; 6 for Mountain and seven for Pacific or use this converter. The subsequent column tells you which of them satellite tv for pc eclipses (e) or occults (o) one other. For instance, 1E4 implies that satellite tv for pc I (Io) casts its shadow on satellite tv for pc IV (Callisto). In 3O2, satellite tv for pc III (Ganymede) covers II (Europa).

Mutual phenomena diagram
Two mutual occasions seen from the Americas in April are depicted right here intimately. UT occasions are proven in green beneath every stage. During the Ganymede eclipse, the fuzzy gray-black disk is Io’s shadow.
Created with the free WinJUPOS program

The columns that observe give the length of the occasion in minutes; the influence issue ( “0” signifies the satellite tv for pc passes centrally by way of the shadow or behind the obvious disk of the opposite satellite tv for pc, whereas “1” is a grazing occasion, and unfavorable values point out the motion happens in entrance of or behind Jupiter’s disk); M is the mixed magnitude of the satellites; Δm is change in magnitude of the 2 moons earlier than and at the time of the occasion; limb is the obvious distance of the concerned satellite tv for pc from the planet’s limb (in arcseconds); and dist the space between the 2 satellites (in arcseconds).

For an exquisite sampling of pictures and animations from earlier mutual occasions seasons, remember to try the Mutual Events site maintained by avid planetary imager Marc Delcroix.

Mutual phenomena are dynamic occasions, simply the factor to boost your observing this season. Pull up a telescope and dance the evening away with Jupiter’s moons.

Playing Hide-and-Seek with 44 Capricorni

Jupiter's Io and 44 Cap appulse
Jupiter’s moon Io (magnitude 5.9) passes extraordinarily near 44 Capricorni at daybreak on April 2nd.

A unique form of occultation occurs at daybreak on April 2nd when the 5.9-magnitude star 44 Capricorni has shut encounters of a number of varieties at Jupiter. As seen from western and central South America, Jupiter will occult the star. Observers in jap North America will witness the star reappear at the planet’s western limb in twilight, at round 6 a.m. EDT. Since Jupiter will probably be low within the southeastern sky at the time (~12° from 40°N), ensure you discover a spot with an unobstructed view.

Observers within the Midwest will miss the occultation however could have front-row seats when Io passes simply 0.5″ south of 44 Capricorni round 5:21 a.m. CDT (6:21 EDT for the jap Midwest). The two equally vivid objects will seem to just about merge after which separate over the span of about 10 minutes. From some areas in Central America and northwestern South America Io will occult 44 Capricorni. For instance, in San José, Costa Rica, Io covers the star between 4:18 and 4:20 a.m.


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