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NASA’s Astronomy Picture of the Day for Oct. 28, 2026, features a video of Ganymede briefly blocking Io from view during an event on Oct. 20. The alignment is a mutual occultation, a type of event visible when Earth’s view of Jupiter’s Galilean moons’ orbits is nearly edge-on.
NASA’s Astronomy Picture of the Day on Oct. 28, 2026, features a video of Ganymede briefly passing in front of Io, two of Jupiter’s large moons. The event occurred on Oct. 20 and is a mutual occultation, an alignment that can be observed when Earth has a nearly edge-on view of the moons’ orbits.
The APOD explanation, written by astronomer Michael Wong, says the video captures Ganymede blocking Io from view for a short time. An occultation occurs when one celestial object passes in front of another and partly or completely hides it from a particular viewpoint. The image’s focus is the apparent overlap of the moons as seen from Earth, not a collision or close physical encounter between them.
The NASA page also notes that Ganymede casts a shadow on Jupiter in the scene, on the planet’s right side. That shadow would produce a solar eclipse for an observer located within it on Jupiter, Wong writes. The page describes the feature as a video and credits it to Michael Wong; it does not provide measurements of the occultation’s duration or the moons’ apparent sizes in the supplied explanation.
The APOD is dated Oct. 28, 2026, eight days after the reported alignment. NASA’s page presents the event as that day’s featured astronomy image, accompanied by an explanation and credits for the image and editors. Its account identifies the two moons and the date of their apparent meeting, but does not state that the video represents a new discovery.
A Rare View of Jupiter’s Moons
The alignment makes visible a feature of the orbital geometry of Jupiter’s major moons. Mutual occultations of the Galilean moons are rare to witness from Earth because the viewing angle must place one moon in front of another. NASA’s explanation says the necessary edge-on view occurs around Jupiter’s equinox, when the planet appears less tilted from Earth.
For readers, the video offers a direct illustration of how changing viewpoints shape astronomical observations: the moons appear to overlap even though the event is an alignment along our line of sight. The accompanying shadow adds another demonstration of the same geometry, showing how a moon can block sunlight from reaching part of Jupiter. The feature is an educational presentation of an observed event; the source does not report a new scientific finding arising from it.
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Jupiter’s Moons and Viewing Angle
Io and Ganymede are among Jupiter’s four Galilean moons, named for the group first observed by Galileo Galilei. The other two are Europa and Callisto. The APOD explanation focuses specifically on the Oct. 20 apparent alignment between Io and Ganymede, viewed from Earth, and on Ganymede’s shadow falling across Jupiter.
According to Wong’s explanation, mutual occultations of Galilean moons become observable when Earth sees the moons’ orbital plane nearly edge-on. This viewing configuration recurs about once every six years, as Jupiter reaches equinox. That timing describes the repeating opportunity for this kind of alignment; it does not mean that the same pair of moons necessarily produces an identical event each time.
The page also gives a count of 115 known moons orbiting Jupiter and compares it with Saturn’s 293. Those figures are presented in the APOD explanation, rather than as the main news development. The central subject of the Oct. 28 entry is the video of the mutual occultation and its accompanying explanation.
Details the APOD Does Not Give
The supplied APOD explanation does not specify how long Io was obscured, whether it was fully or partly hidden throughout the event, or the precise location and equipment used to record the video. It also does not provide timing details beyond giving Oct. 20, 2026, as the date of the moons’ meeting.
The page describes a recurring viewing opportunity around Jupiter’s equinox, but does not give a schedule for future mutual occultations or say when another event involving this particular pair will be visible. The quoted six-year interval should be read as the approximate recurrence of the edge-on viewing configuration, not a detailed forecast.
The Next APOD Features
The NASA page lists the next Astronomy Picture of the Day as “a planet grows horns,” but the supplied source does not provide further information about that image or its subject. The Oct. 28 entry itself is a dated presentation of the Oct. 20 event; it does not announce additional observations, analysis or follow-up research.
Readers seeking more about the recording would need details beyond the APOD explanation, including its observational setup and exact event timing. Based on the material provided, the confirmed next step is simply the publication of the following APOD feature, while the Oct. 20 mutual occultation remains the subject of the current entry.
Key Questions
What happened between Ganymede and Io?
Ganymede passed in front of Io from Earth’s viewpoint on Oct. 20, 2026, briefly blocking the other moon from view. NASA’s APOD featured a video of the event on Oct. 28.
What is a mutual occultation?
It is an event in which one astronomical object passes in front of another and partly or completely blocks it from a particular viewpoint. In this case, Ganymede appeared to obscure Io.
Why are these events rare to see?
They require Earth’s view of the Galilean moons’ orbits to be nearly edge-on, so one moon can line up in front of another. The APOD explanation says this configuration recurs about every six years around Jupiter’s equinox.
What is the shadow on Jupiter?
NASA’s explanation says Ganymede is casting a shadow on Jupiter’s right side. An observer within the shadow on Jupiter would experience a solar eclipse, according to the APOD.
Source: science.nasa.gov
