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Moon occults Jupiter before dawn on Oct. 6 for eastern North America
Jupiter slips behind a crescent moon near 10:16 UT on Oct. 6, before dawn for the eastern US and Canada, in the last good view from the lower 48 until 2034. Saturn reaches opposition two days earlier, brightening by about 0.3 magnitudes, a change skywatchers can test against Capella and Rigel.
The Scientist · Science desk
What happened
- Jupiter, at magnitude -1.9 and 34 arcseconds across, will take a full minute to disappear behind the moon and another full minute to reappear.
- The 20%-lit waning crescent leads with its sunlit edge, so Jupiter vanishes at the bright limb and comes back out at the dark one.
- Because Saturn's opposition falls near September's equinox, the planet strays just into a corner of Cetus, a constellation outside the zodiac.
- Saturn's rings are tilted 12 degrees in late 2026, opening from edge-on in 2025 toward their widest tilt in 2031.
Why it matters
- capability A minute-long fade at each edge of the moon is slow enough to watch and record on video, so the event suits camera owners as well as observers at the eyepiece.
- decision Anyone planning to record it needs their own site's ingress and egress times from IOTA's list, since contact times move with location away from the event's center time.
- constraint The 0.3-magnitude surge depends on how far the rings are open, so this year's figure will not hold for the oppositions to come as the rings widen toward 2031.
The one-minute fade follows from two other figures in the phys.org account. The moon covers its own apparent diameter, half a degree, in about an hour [3]. Half a degree is 1,800 arcseconds, so the lunar edge sweeps about 30 arcseconds a minute, and a 34-arcsecond disk takes roughly 68 seconds to go under [9]. That matches the article's full minute for both the disappearance and the return [4].
For the East Coast the center of the event falls at 6:16 a.m. EDT [23]. Last month's occultation of Jupiter happened in daylight. This one is in darkness before sunrise across the eastern contiguous US and Canada [2]. Phys.org calls it one of the best-placed and top sky events of 2026 [7]. The moon's unlit side should show faintly in earthshine [6], and Jupiter's own moons are in their mutual transit season at the same time [10].
I think the better experiment of the week is Saturn's, because it comes with controls. At opposition the planet shows a fully lit face to Earth, and a retroreflective brightening called the Seeliger effect, or opposition surge, sets in [14]. The rings make Saturn's version especially prominent, at about 0.3 magnitudes [15]. The article gives its own conversion: six times brighter is about two magnitudes. By that ratio, 0.3 magnitudes is about 30 percent brighter [20].
The lunar example in the same piece needs a denominator. A moon near full can be up to six times as bright as a quarter moon [16], but the quarter moon is only 50% lit. Doubling the lit fraction accounts for a factor of two. The remaining factor of about three is what the article credits to the small shadows that vanish at full phase [21].
The controls are Capella and Rigel, both zero magnitude, against Saturn at +0.3 [17]. Saturn therefore sits 0.3 magnitudes fainter than its comparison stars, a gap the same size as the surge [22]. The thing this doesn't tell you is whether the +0.3 figure already includes the surge. An observer can still follow the change against the same two stars over the next few weeks as the surge fades [17].
What to watch
- Cloud cover over the eastern US and Canada in the hours before dawn on Oct. 6, since the event is a single predawn window.
- Amateur video of ingress and egress, which would show whether the fade runs close to the 68 seconds the moon's half-degree-per-hour motion predicts.
- Whether ring spokes show up as Saturn comes off its 2025 equinox season; phys.org says they are thought to come from meteoroid impacts.
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- [1]
The moon is a 20% illuminated waning crescent when it covers Jupiter; the illuminated side leads as Jupiter disappears, and Jupiter reappears from behind the moon's dark limb.
- [2]
Unlike last month's daytime event, this occultation of Jupiter occurs under predawn skies for the eastern contiguous United States and Canada.
- [3]
The moon moves by its own apparent diameter of half a degree about once every hour; ingress and egress times vary by location.
- [4]
Jupiter, at magnitude -1.9, is 34 arcseconds in apparent size and will take a full minute to disappear or reappear from behind the moon.
- [5]
IOTA has a list of ingress/egress times for select sites along the path.
- [6]
The nighttime side of the moon will be lit by earthshine during the occultation.
- [7]
Phys.org describes the October occultation of Jupiter as one of the best-placed and top skywatching events for 2026.
- [8]
The slow, minute-long occultation lends itself to observing and recording on video.
- [9]
The lunar edge sweeps about 30 arcseconds per minute, so Jupiter's 34-arcsecond disk takes roughly 68 seconds to be covered.
- [10]
The occultation takes place during mutual transit season for Jupiter's moons, currently underway.
- [11]
Saturn reaches opposition for 2026 on Oct. 4; falling near last month's equinox, this puts Saturn just into the corner of the non-zodiacal constellation Cetus.
- [12]
The tilt of Saturn's rings is 12 degrees in late 2026, widening from edge-on in 2025; the rings will again reach their widest tilt in 2031.
- [13]
Spokes on Saturn's rings, radial streaks across the ring plane, may be visible coming off last year's equinox season and are thought to be due to meteoroid impacts.
- [14]
Near opposition Saturn shows the Seeliger effect, or opposition surge, a retroreflective phenomenon as the planet reaches a 100% illuminated phase from our viewing angle.
- [15]
Saturn's opposition surge is especially prominent due to its extended rings, amounting to about 0.3 magnitudes in brightness.
- [16]
The moon near full phase becomes up to half a dozen times as bright (over two full magnitudes) as the 50% illuminated first- or last-quarter moon.
- [17]
Saturn is at magnitude +0.3; zero-magnitude stars Capella and Rigel offer a good comparison as the surge fades over the next few weeks.
- [18]
The size of Saturn's opposition surge varies based on how wide open the rings are near opposition.
- [19]
Saturn's opposition on Oct. 4 comes two days before the Oct. 6 occultation of Jupiter.
- [20]
Using the article's own ratio of about six times brighter per two magnitudes, a 0.3-magnitude surge is about 30 percent brighter.
- [21]
Going from a 50% lit quarter moon to a fully lit moon doubles the lit fraction, accounting for a factor of two of the up-to-sixfold brightening; the remaining factor is about three.
- [22]
At magnitude +0.3, Saturn sits 0.3 magnitudes fainter than the zero-magnitude comparison stars Capella and Rigel, the same size as the opposition surge.
- [23]
The lunar occultation of Jupiter takes place in the early morning of Tuesday, Oct. 6, 2026, centered on 10:16 Universal Time / 6:16 a.m. EDT.
- [24]
The next good lunar occultation of Jupiter for the contiguous US is on Sept. 28, 2034.
- [25]
The gap between the Oct. 6, 2026 occultation and the next good one for the contiguous US on Sept. 28, 2034 is just under eight years.
Sources
3 independent publishers whose own reporting we read for this story.
- livescience.comJupiter will disappear behind the moon in a once-in-a-decade alignment tomorrow
1 article · October 5, 2026
- phys.orgCatch a rare lunar occultation of Jupiter plus Saturn at opposition in early October
1 article · September 30, 2026
- space.comJupiter will disappear behind the moon on Oct. 6 — and if you're in the right place, you can watch it happen
1 article · October 2, 2026
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