You’re Invited to Jupiter’s Big, Bright Opposition Bash – Sky & Telescope

I can’t resist Jupiter’s pull and I’m only half joking. Venus may surpass it in brightness, but at magnitude –2.8, Jupiter makes the more dazzling impression this season because of altitude and visibility in a dark sky. On December 7th the gas giant arrives at opposition and holds court from sunset till sunrise. Pinned between the horns of Taurus, the Bull, the mighty planet basks in the glittery company of the Hyades and Pleiades star clusters at the ear-popping declination of +22°. The last time it was this close, this big, and this bright was in November 2023.

Binoculars will show Jupiter as a disk surrounded by up to four moons depending on their proximity to the planet and whether they pass in front of or behind it on a given night. I’ve listed several excellent opportunities when all four are splayed out and particularly binocular-worthy . Times are CST and approximate. Add 1 hour for EST, subtract 1 hour for MST and 2 hours for PST.

• Dec. 4 (8 p.m.)
• Dec. 6 (8 p.m. — best spread!)
• Dec. 18 (11 p.m.)
• Dec. 19 (12:30 a.m.)
• Dec. 21 (1 a.m.)
• Dec. 26 (1 a.m.)
• Dec. 26 (8 p.m. and again around midnight)

The same nights make ideal opportunities to photograph Jupiter and the four Galilean moons with a modest 200-mm telephoto lens. Be out during twilight when the sky is still light, and Jupiter is low enough to include a foreground. Set the ISO to 1600 and the lens wide-open to allow in the maximum amount of light. Then focus the planet sharply on the camera’s backscreen using live view and snap a few exposures between ⅕ second and 3 seconds. Check the results on the replay and adjust the ISO / exposure length accordingly. This works well with digital and mirrorless cameras. For smartphone users, your best bet is to hold the camera over the eyepiece of a small, low-magnification telescope.

Galilean shuffle

Io, Europa, and Ganymede routinely transit in front of Jupiter and cast shadows on its cloud tops. In order of size, Europa casts the smallest, followed by Io, Callisto, and Ganymede. They’re also eclipsed by the planet’s shadow and disappear and reappear at its limb during occultations. You can use Sky & Telescope‘s Jupiter’s Moons interactive observing tool to find out exactly when these events happen for your location.

Because Jupiter’s north pole is currently tipped about 3° toward Earth and the moons orbit in the equatorial plane they cross the planet’s face south of the equator. Callisto, the outermost of the quartet, is distant enough that both its shadow and disk miss the planet entirely, passing above or below it. When Jupiter’s equatorial plane is more closely aligned with Earth’s orbit, as it will starting next summer, the icy moon will have its turn in the game.

Single shadow transits are fairly common but double transits, when two moon shadows dot the disk simultaneously, are infrequent. Happily, two are slated for this month and visible in U.S. time zones. Both involve Io and Ganymede. On December 23rd the two will co-habit Jupiter’s disk from 1:47-2:51 a.m. CST. The second shadow pairing happens a week later on December 30th and will be best visible in the western half of the U.S. and Canada.

Dec. 23 Double Shadow Transit (CST)

• 12:37 a.m. Ganymede’s shadow enters the disk
• 1:47 a.m. Io’s shadow enters the disk
• 2:51 a.m. Ganymede’s shadow leaves the disk
• 3:59 a.m. Io’s shadow leaves the disk

Dec. 30 Double shadow transit

• 3:42 a.m. Io’s shadow enters the disk
• 4:37 a.m. Ganymede’s shadow enters the disk
• 5:54 a.m. Io’s shadow leaves the disk
• 6:52 a.m. Ganymede’s shadow leaves the disk

All this happens against the backdrop of Jupiter’s magnificent clouds, which are organized into alternating dark belts and bright zones. In a 60-mm refractor the SEB and NEB lie on either side of the bright EZ like the chocolate wafers of an Oreo cookie that cap a sweet cream filling. Larger scopes reveal more bands, finer textures, and distinctive colors. In my 10-inch Dob at 200× and higher the primary belts have the same ruddy-brown hue as red oak leaves in autumn.

Busy SEB season

On November 11th, Moisés Portillo recorded a tiny bright spot in the SEB marking a new eruption site of high clouds. Outbreaks of material rising from below Jupiter’s visible cloud tops occur routinely if irregularly. At times a disturbance can propagate and completely alter the appearance of a major cloud belt as happened in 2007, so keep your eyes on this one. During moments of good seeing on December 2nd at 4:15 UT I easily spotted it in my 10-inch Dob as a white, diagonal “crack” in the SEB at 214×. For current news on Jovian weather consult the BAA Jupiter Section Facebook page.

Jupiter rotates faster at the equator than elsewhere, giving it two systems of rotation — System I (9 hours 50.5 minutes) for the EZ, and System II (9 hours 55.7 minutes) for the rest of the planet. In early December the SEB disturbance had a System II longitude of 321°. To see it in your scope, go to the Jupiter’s Moons interactive observing tool. You’ll find the System II longitude of the central meridian under the Basic Data heading. Check to see if that longitude is facing your direction the night you plan to observe or arrange your observing time to include it.

The planet is home to a myriad of storms and cyclones shaped like white or dark ovals and embedded within and between cloud belts or bunched in the polar regions. Despite its slow but steady shrinkage in recent decades, the biggest and longest-lasting storm remains the Great Red Spot (GRS). This season it’s rose-pink but small enough to elude detection in average seeing in 6- or 8-inch scopes at lower magnifications. Even in my 10-inch I had to power up recently past 200× for a clear view. It helps that the Spot occupies a lighter-colored “hollow.” Like a photo in a frame, the vacuity helps to highlight its ever-diminishing presence.

Whatever your instrument, try to observe it around the time of central meridian crossing. Sky & Telescope‘s GRS calculator will help you find those times. If you have an iPhone or iPad and $2.99, download the JupiterMoons app for a list of events, GRS transit times and moon positions.

The atmosphere will always be the limiting factor when it comes to glimpsing Jovian detail. Many amateurs opt for planetary cameras or smart telescopes and use programs that select and stack only the best images to create exceptionally detailed portraits of Jupiter and the four bright moons. If you’re a visual observer your best strategy is to maintain a steady vigil and collect as many moments of good seeing as possible. I divide Jupiter into sections — the GRS region, EZ festoons, or NEB texture — and lavish attention on each in turn to assemble a complete mental image of the planet. Then I’ll go inside to warm up and sketch what I saw. Sketching is one of the best ways to really see a subject because it concentrates the mind to notice details.

Jupiter’s full name in Roman mythology was Jupiter Optimus Maximus (Jupiter Best and Greatest). Spend an hour with the king of the gods and I think you’ll find that no other planet is more rewarding to watch.

Resources

Jupiter 2024 Season — Superb imagery and informative commentary by planetary photographer Christopher Go
Association of Lunar and Planetary Observers (ALPO) Jupiter Section — Clearinghouse for observations and information
British Astronomical Association (BAA) Jupiter Section — Excellent site for current Jupiter news
JUPOS.org — Database of object positions on Jupiter