A Late-Night Jupiter Occultation

Moon occults Jupiter
The waning crescent Moon is about to occult Jupiter on the morning of October 19, 1968.
Courtesy John Asztalos.
If you missed the blue-sky occultation of Jupiter that happened in broad daylight on November 9, 2004, don’t fret. A more dramatic repeat is at hand, this time in the deepest dark of night. On the morning of December 7th, the thick waning crescent Moon will rise in the east around 2 a.m. local time with bright Jupiter shining close by its sunlit side. As the eerie pair rises higher in the sky, the Moon will draw closer to the planet. Observers in eastern and central North America can then watch as Jupiter disappears behind the Moon’s bright limb, as shown below. The planet reappears out from behind the Moon’s dark, dimly earthlit limb roughly an hour later. Jupiter’s disappearance and reappearance will each take about a minute, while the Moon’s edge advances across the giant planet’s 33-arcsecond-wide face. You’ll need a telescope to watch the disappearance next to the Moon’s dazzlingly daylit landscape, but the reappearance will be easily visible to the naked eye — though of course binoculars or a telescope will give a far more impressive view.

Where Jupiter's disappearance and reappearance is visible
For your location, interpolate between the purple or red curves to find the Universal Time of Jupiter’s disappearance (above) and reappearance (below), and between the green curves to find the planet’s altitude above your east-southeast horizon at these times. Even at sites where no occultation happens, the Moon and Jupiter will make a striking, very close pair in the predawn sky.
Sky & Telescope illustration.
Use the two maps (at left and below) to find the circumstances of the disappearance and reappearance at your site. Put a pencil dot on your location, and interpolate between the purple or red lines to find the Universal Time (UT) of the event. (To get Eastern Standard Time, subtract 5 hours from UT; to get Central Standard Time, subtract 6 hours; to get Mountain, subtract 7.) Then interpolate between the green lines to find the altitude of Jupiter and the Moon above your east-southeast horizon at this time. Since the altitude will be rather low at most locations, especially for the disappearance, you may want to scout out an observing site in advance that has a low enough view toward the east-southeast.

Where Jupiter's disappearance and reappearance is visible
For your location, interpolate between the purple or red curves to find the Universal Time of Jupiter’s disappearance and reappearance, and between the green curves to find the planet’s altitude above your east-southeast horizon at these times. Even at sites where no occultation happens, the Moon and Jupiter will make a striking, very close pair in the predawn sky.
Sky & Telescope illustration.
A telescope will also show occultations of Jupiter’s Galilean moons: Callisto roughly 14 minutes before Jupiter itself (depending on your location), Ganymede about 4 minutes before, and Europa roughly 2 minutes after. Io is in occultation by Jupiter itself, until it emerges from behind the planet’s eastern limb at 10:12 UT.

Another bonus for telescope users is that the bright side of the Moon — the lunar west (celestial east) side — will be librated (tipped) into especially good view. Therefore we’ll get a chance to catch sight of elusive Mare Orientale, along with the associated Lacus Autumni and Lacus Veris, on the limb southward from dark Grimaldi — as described and pictured in the article "A Rare Glimpse of Mare Orientale."

Jupiter passing behind the Moon as seen from various cities
Jupiter’s path behind the Moon as seen from various cities. Celestial north is up, and celestial east (lunar west) is left.
Sky & Telescope illustration.
The occultation will offer a chance for some interesting astrophotography. If you want Jupiter to come out looking larger than a dot, you’ll need to use the afocal technique: shooting through an eyepiece rather than mating a camera body to the telescope itself. Digital point-and-shoots work well for this; buy or make a bracket to hold the camera pointed squarely into the eyepiece (see "Astro Imaging with Digital Cameras"). Experiment beforehand to get everything working right.

Longtime Jupiter observers may be surprised at the planet’s dim surface brightness compared to the sunlit Moon. After all, Jupiter is covered with bright clouds (average albedo 52 percent), while the Moon’s surface is very dark gray dust (average albedo 12 percent). However, this can’t make up for the fact that Jupiter is about six times farther from the Sun — and is therefore illuminated by sunlight that’s only 1/36 as bright.

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