{"id":17858,"date":"2026-09-26T09:16:12","date_gmt":"2026-09-26T07:16:12","guid":{"rendered":"https:\/\/deep-space-astronomy.ch\/?p=17858"},"modified":"2026-09-26T09:16:12","modified_gmt":"2026-09-26T07:16:12","slug":"saison-eclipses-mutuelles-lunes-jupiter-2026-ballet-satellites-galileens","status":"publish","type":"post","link":"https:\/\/deep-space-astronomy.ch\/en\/saison-eclipses-mutuelles-lunes-jupiter-2026-ballet-satellites-galileens\/","title":{"rendered":"Season of Mutual Eclipses of Jupiter's Moons: Watch the Ballet of the Galilean Moons"},"content":{"rendered":"<div class=\"product\"><div class=\"product\"><p>About every five years, the orbits of Jupiter\u2019s four largest moons align as seen from Earth. For a few months, one moon passes in front of another, or its shadow crosses in front of another. This is the season of mutual eclipses, and it\u2019s in full swing right now. The peak of the season is in mid-October 2026. It\u2019s an event not to be missed.<\/p>\n<h2>What is a mutual eclipse?<\/h2>\n<p>Imagine this: You\u2019re on Jupiter, looking at the Sun. If a moon passes in front of the Sun, you see a solar eclipse. Now imagine you\u2019re on a moon, and another moon passes in front of the Sun: you\u2019ll also see a solar eclipse. That\u2019s exactly what happens during a mutual eclipse.<\/p>\n<p>As seen from Earth, two types of events occur:<\/p>\n<ul>\n<li><strong>Blackout<\/strong> : One moon passes in front of another. The two moons seem to merge into a single point, then separate. It's like a double star that moves closer and farther away.<\/li>\n<li><strong>Eclipse<\/strong> : The shadow of one moon passes across the disk of another. The eclipsed moon slowly fades, sometimes until it disappears completely, then reappears. It\u2019s like watching a light dim and then brighten again.<\/li>\n<\/ul>\n<p>Like solar eclipses on Earth, each event has three types: total (completely obscured), annular (ring-shaped), and partial (only a portion is obscured).<\/p>\n<h2>Why now?<\/h2>\n<p>The orbits of the Galilean moons lie almost in Jupiter\u2019s equatorial plane, which is itself inclined by a little more than 3\u00b0 relative to Jupiter\u2019s orbit around the Sun. Most of the time, the moons pass above or below one another as seen from Earth. But about every five years, when Earth crosses Jupiter\u2019s equatorial plane, the orbits align and mutual eclipses become possible.<\/p>\n<p>The current season began when Jupiter entered conjunction with the Sun on July 29, 2026. Events have been occurring with increasing frequency ever since. The season peaks in mid-October 2026. The season lasts until early 2027, with Jupiter in opposition on February 11, 2027.<\/p>\n<p>The next triple shadow (three moons casting their shadows on Jupiter simultaneously) is expected in March 2032. The last one occurred in January 2015. This season is therefore an event not to be missed.<\/p>\n<h2>The Four Galilean Moons<\/h2>\n<p>Jupiter has 95 known moons, but only four are visible through an amateur telescope: the Galilean moons, discovered by Galileo in 1610.<\/p>\n<ul>\n<li><strong>Io<\/strong> : the closest to Jupiter, the most volcanically active in the Solar System. Apparent diameter: about 1.0\u2033. Intense volcanic activity, yellow-orange surface.<\/li>\n<li><strong>Europe<\/strong> : The second one, covered in ice, with an ocean of liquid water beneath its crust. Diameter: about 1.1\u2033. It is the most interesting moon for the search for extraterrestrial life.<\/li>\n<li><strong>Ganymede<\/strong> : the largest moon in the Solar System, larger than Mercury. Apparent diameter: about 1.3\u2033. It is the largest and easiest to spot.<\/li>\n<li><strong>Callisto<\/strong> : the farthest, the most heavily cratered. Diameter: about 1.2\u2033. It is the only one of the four that can sometimes \u00abmiss\u00bb Jupiter, because its orbit is the most inclined.<\/li>\n<\/ul>\n<p>The three inner moons (Io, Europa, and Ganymede) are in a 1:2:4 resonance: Io completes two orbits for every one completed by Europa, and Europa completes two orbits for every one completed by Ganymede. This resonance keeps their orbits stable and synchronized.<\/p>\n<h2>How to Observe<\/h2>\n<h3>The telescope<\/h3>\n<p>The Galilean moons are tiny: Ganymede, the largest, has a disk measuring barely 1.3 arcseconds. By comparison, Saturn\u2019s disk measures 19 arcseconds. But mutual eclipses do not require resolving the moons\u2019 disks: it is enough to observe the dimming of brightness when the shadow of one moon passes across another.<\/p>\n<p>A telescope with a diameter of 100\u2013150 mm is sufficient for observing mutual eclipses. At a magnification of 100x to 200x, the four moons are clearly separated from Jupiter, and changes in brightness are detectable. A larger telescope (200\u2013250 mm) allows for better resolution of the moons and enables you to see the occultations as distinct mergers.<\/p>\n<h3>When to observe<\/h3>\n<p>Jupiter is currently visible before dawn in the constellation Leo. In October 2026, Jupiter rises around 11:00 p.m. to midnight and reaches its highest point in the sky in the early morning. The best time to observe it is between 1:00 a.m. and 5:00 a.m., when Jupiter is high in the sky.<\/p>\n<p>Jupiter will be in opposition on February 11, 2027: at that time, Jupiter will be visible all night long and will reach a maximum altitude of about 50\u00b0 as seen from Switzerland.<\/p>\n<h3>Predictions<\/h3>\n<p>To know when to observe them, you need predictions of mutual events. Several resources are available:<\/p>\n<ul>\n<li><strong><a href=\"https:\/\/www.imcce.fr\/phemu\/\" target=\"_blank\" rel=\"noopener\">IMCCE (Institute of Celestial Mechanics and Ephemeris Computation)<\/a><\/strong> : The French observatory publishes comprehensive predictions of the mutual phenomena of the Galilean moons. It is the authoritative source.<\/li>\n<li><strong><a href=\"https:\/\/pds-rings.seti.org\/tools\/tracker3_jup.shtml\" target=\"_blank\" rel=\"noopener\">SETI PDS Rings Node<\/a><\/strong> : The SETI Institute's tool for predicting the positions and phenomena of Jupiter's moons.<\/li>\n<li><strong><a href=\"https:\/\/stellarium.org\/\" target=\"_blank\" rel=\"noopener\">Stellarium<\/a><\/strong> : The free planetarium shows the positions of the moons and simulates celestial phenomena. Very useful for planning a session.<\/li>\n<li><strong><a href=\"https:\/\/britastro.org\/section_news_item\/mutual-events-of-the-galilean-satellites-2026-27\" target=\"_blank\" rel=\"noopener\">British Astronomical Association<\/a><\/strong> : The BAA has published a guide for the 2026\u20132027 season.<\/li>\n<\/ul>\n<h3>The Technique<\/h3>\n<ol>\n<li><strong>Check the predictions<\/strong> : Note the date, time, and type of event (occultation or eclipse, and which moons).<\/li>\n<li><strong>Get there early<\/strong> : Please arrive 30 minutes before the event to allow the telescope to adjust to the temperature.<\/li>\n<li><strong>Look for the four moons<\/strong> : At 100-200x magnification, the four Galilean moons are visible as bright spots around Jupiter.<\/li>\n<li><strong>Observe the moon in question<\/strong> : During an eclipse, the eclipsed moon slowly fades. During an occultation, the two moons move closer together, merge, and then separate.<\/li>\n<li><strong>Make a note of the time<\/strong> : Events last from a few minutes to half an hour. Note the start, peak, and end times.<\/li>\n<\/ol>\n<h3>Recognizing the Moons<\/h3>\n<p>An experienced observer can identify which moon is casting the shadow based on its appearance: Callisto\u2019s shadow is broad and diffuse, while Io\u2019s is a sharp black dot. Europa and Ganymede fall somewhere in between. But for a beginner, the easiest approach is to note the moons\u2019 positions in Stellarium before observing and then identify them based on their positions.<\/p>\n<h2>For the photo<\/h2>\n<p>Mutual eclipses pose a challenge for astrophotography because of the small size of the moons (1\u20131.3\u2033). However, a planetary camera (Player One Mars, ZWO ASI462) paired with a 200 mm telescope and a 2x or 3x Barlow lens can capture the occultations as two points merging together.<\/p>\n<p>For eclipses (brightness attenuation), the method is different: we measure the moon\u2019s brightness with a camera and plot the brightness curve as a function of time. This is photometry, not imaging. A digital camera in video mode, or a continuous-exposure planetary camera, can record the decrease in brightness.<\/p>\n<h2>Why It's Special<\/h2>\n<p>Mutual eclipses of Jupiter\u2019s moons are a rare and subtle phenomenon. They do not produce spectacular images like those of a nebula or a galaxy, but they offer something no other observation can: the sensation of seeing the Solar System in motion, in real time, right before your eyes.<\/p>\n<p>When you see Io\u2019s shadow pass across Ganymede, what you\u2019re seeing is a solar eclipse as viewed from Ganymede. And when the two moons merge into a single point and then separate, you\u2019re witnessing an orbital ballet that has been unfolding for 4.5 billion years.<\/p>\n<p>The season lasts until early 2027. The peak is now, in mid-October 2026. Get your telescope out.<\/p>\n<p><em>Sources : <a href=\"https:\/\/www.universetoday.com\/articles\/catching-2026-jovian-moon-mutual-eclipse-season\" target=\"_blank\" rel=\"noopener\">Universe Today \u2013 Catching the 2026 Season of Mutual Eclipses of Jupiter's Moons<\/a> ; <a href=\"https:\/\/britastro.org\/section_news_item\/mutual-events-of-the-galilean-satellites-2026-27\" target=\"_blank\" rel=\"noopener\">British Astronomical Association \u2013 Joint Events 2026\u201327<\/a> ; <a href=\"https:\/\/www.imcce.fr\/recherche\/campagnes-observations\/phemus\/phemu\" target=\"_blank\" rel=\"noopener\">IMCCE \u2013 Phemu<\/a> ; <a href=\"https:\/\/skyandtelescope.org\/astronomy-news\/observing-news\/mutual-event-season-heats-up-at-jupiter\/\" target=\"_blank\" rel=\"noopener\">Sky &amp; Telescope \u2013 Mutual Event Season<\/a><\/em><\/p>\n<p><em>See also on Deep Space Astronomy: <a href=\"https:\/\/deep-space-astronomy.ch\/en\/saturne-opposition-4-octobre-2026-guide-observation-seigneur-anneaux\/\">Saturn in opposition on October 4, 2026<\/a> ; <a href=\"https:\/\/deep-space-astronomy.ch\/en\/draconides-9-octobre-2026-essaim-atypique-observer-tombee-nuit\/\">Draconids on October 9, 2026<\/a><\/em><\/p>\n<p><em>Signature: CBurkhalter<\/em><\/p>\n<\/div><\/div>","protected":false},"excerpt":{"rendered":"<p>Every five years, the orbits of the Galilean moons align as seen from Earth. One moon eclipses another, or its shadow passes across another. Active period: late 2026\u2013early 2027, peaking in mid-October. Observation guide for 100\u2013150 mm telescopes, with predictions from IMCCE and Stellarium.<\/p>","protected":false},"author":187,"featured_media":17857,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[827],"tags":[],"class_list":["post-17858","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-actualites"],"_links":{"self":[{"href":"https:\/\/deep-space-astronomy.ch\/en\/wp-json\/wp\/v2\/posts\/17858","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/deep-space-astronomy.ch\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/deep-space-astronomy.ch\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/deep-space-astronomy.ch\/en\/wp-json\/wp\/v2\/users\/187"}],"replies":[{"embeddable":true,"href":"https:\/\/deep-space-astronomy.ch\/en\/wp-json\/wp\/v2\/comments?post=17858"}],"version-history":[{"count":1,"href":"https:\/\/deep-space-astronomy.ch\/en\/wp-json\/wp\/v2\/posts\/17858\/revisions"}],"predecessor-version":[{"id":17859,"href":"https:\/\/deep-space-astronomy.ch\/en\/wp-json\/wp\/v2\/posts\/17858\/revisions\/17859"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/deep-space-astronomy.ch\/en\/wp-json\/wp\/v2\/media\/17857"}],"wp:attachment":[{"href":"https:\/\/deep-space-astronomy.ch\/en\/wp-json\/wp\/v2\/media?parent=17858"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/deep-space-astronomy.ch\/en\/wp-json\/wp\/v2\/categories?post=17858"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/deep-space-astronomy.ch\/en\/wp-json\/wp\/v2\/tags?post=17858"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}