Moon to Block Jupiter for 1 Hour on Oct. 6, a Rarity Not Seen Again for 11 Years

Q: As the crescent moon blocks Jupiter tomorrow, can you spot the planet's gradual disappearance and its four largest moons without a telescope?

Yes — you can likely see Jupiter’s reappearance with the naked eye, but following its full gradual disappearance is much easier with binoculars or a small telescope, and its four largest moons generally are not reliably visible without optical aid. Jupiter will not blink out instantly like a star. Because it has a visible disk, the Moon takes about a minute to cover it and about a minute to uncover it. The harder part is the disappearance: Jupiter goes behind the Moon’s bright sunlit edge, whose glare is so strong that most observers will need binoculars or a telescope to clearly watch the planet fade from view. The reappearance is different. Jupiter emerges from the Moon’s dark, earthshine-lit limb, and under good skies that should be visible even without a telescope. As for the Galilean moons — Io, Europa, Ganymede and Callisto — they are typically a binocular or telescope target. In very dark conditions, exceptionally sharp-eyed observers can sometimes glimpse one or more of them without aid when they are far enough from Jupiter, but that is unusual. For this event, the Moon’s glare and the low pre-dawn sky make naked-eye sightings of the moons especially unlikely. So if you are watching without equipment, focus on the broader spectacle: Jupiter near the crescent Moon and its bright “return” from the dark edge. If you want to track the planet’s slow disappearance and have a realistic chance of seeing the moons, bring binoculars or, better, a small telescope.

Q: Tomorrow morning marks the best Jupiter occultation since 2004; will you wake up early to witness this rare cosmic alignment before 2037?

If you are in the eastern or much of the central U.S. or nearby southern Canada, it is worth waking up early. This is widely described by astronomy sources as the best Jupiter occultation visible from North America since 2004, and the next comparable one visible from North America is not expected until Nov. 27, 2037. The event happens before sunrise Tuesday, Oct. 6, with Jupiter slipping behind the waning crescent moon around 4:15 to 4:20 a.m. EDT in many eastern locations and reappearing roughly an hour later, around 5:24 to 5:30 a.m. Exact times vary by city. In Washington, D.C., for example, the predicted times are about 4:20 a.m. and 5:24 a.m.; New York is about 4:23 a.m. and 5:27 a.m.; Boston about 4:26 a.m. and 5:30 a.m. The best views will be in the East, where the moon and Jupiter will be comfortably above the horizon in a dark sky. Farther west, many observers will miss the disappearance because the pair will still be below the horizon, though some can still catch Jupiter’s reappearance or at least a very close moon-Jupiter pairing after moonrise. The occultation should be visible to the naked eye, especially Jupiter’s reappearance from the moon’s dark, earthshine-lit limb. Binoculars or a small telescope will make the event more dramatic and may also reveal Jupiter’s four Galilean moons. Forecasts call for generally favorable viewing conditions in many areas, making this a strong opportunity for both casual skywatchers and photographers.

Q: Depending on your exact location tomorrow, will you witness a full planetary eclipse or a rare, grazing occultation of Jupiter?

For most people in the eastern and much of central U.S. and southern Canada, it will be a full lunar occultation of Jupiter; only observers near the northern or southern edge of the visibility path are likely to get the rarer grazing occultation. The difference depends entirely on your location. In the main path, the waning crescent moon fully covers Jupiter for up to about an hour before the planet reappears from the moon’s dark, earthshine-lit edge. That is the view expected in cities such as Washington, New York, Boston, Atlanta, Chicago, Detroit, Miami, Toronto, Montreal and Philadelphia, with local timing varying slightly. A grazing occultation happens only near the path’s boundaries, where Jupiter appears to skim the lunar limb instead of being fully hidden. Astronomy forecasts place those edge zones in narrow strips along the northern and southern limits of the occultation track. If you are well inside the eastern or central North American viewing zone, you are much more likely to see a full cover-up than a graze. Farther west, many observers will not see a full occultation at all because the moon and Jupiter are still below the horizon when the event begins. In places such as Denver and other parts of the Rockies and Southwest, viewers may catch only Jupiter’s reappearance or simply a very close moon-Jupiter pairing after moonrise. Along much of the Pacific Coast, the occultation is over before the pair rises.

3 articles · Updated · Livescience.com · Oct 5

Up to 1 hour before dawn Tuesday, Jupiter will vanish behind a 20%-lit waning crescent moon for viewers across much of eastern and central North America and the Caribbean.
The lunar occultation needs no telescope, though binoculars or a small scope will better show Jupiter shrinking from a bright point into a tiny disc as it takes about a minute to disappear fully.
Major-city timings run from 3:22-4:17 a.m. CDT in Chicago to 4:30-5:26 a.m. EDT in Montreal; outside the occultation path, the moon will only appear to skim Jupiter.
The alignment will not be visible again from North America until Nov. 27, 2037, making Tuesday's event the continent's only Jupiter lunar occultation for 11 years.