The sky, Dec. 23-29: The moons of Jupiter

Special to CosmicTribune.com, December 23, 2024

Excerpts from weekly Sky&Telescope report.

■ Last-quarter Moon (exact at 5:18 p.m. EST). The Moon rises around midnight, under the hind feet of Leo.

MONDAY, DECEMBER 23

■ The little Pleiades cluster shines very high in the southeast after dinnertime, no bigger than your fingertip at arm’s length. How many Pleiads can you count with your unaided eye? Take your time and keep looking. Most people can count 6. With extra-sharp eyesight, a good dark sky, and a steady gaze, you may be able to make out 8 or 9.

TUESDAY, DECEMBER 24

■ Right around the end of twilight, face north and look very high. Cassiopeia is now a flattened M canted at an angle, with its left side highest (depending on where you live). Just two hours later, the M is horizontal! Constellations passing near your zenith appear to rotate rapidly with respect to your direction “up.”

WEDNESDAY, DECEMBER 25

■ Tonight at 8:48 p.m. EST, be watching Jupiter in your telescope. Jupiter’s moon Io will slowly reappear out of eclipse from Jupiter’s shadow, just to the planet’s east.

Europa looks on from farther east, while Ganymede and Callisto hang out on Jupiter’s other side.

THURSDAY, DECEMBER 26

■ To the right of bright Jupiter shines orange Aldebaran, which comes with the large, loose Hyades cluster in its background. Binoculars are the ideal instrument for this cluster given its size: its brightest stars (magnitude 3.5 to 5) span an area about 4° wide. Higher above, the Pleiades are hardly more than 1° across counting just the brightest stars.

The main Hyades stars form a V, lying on its side these evenings. Aldebaran forms the lower of the V’s two tips.

With binoculars, follow the lower branch of the V to the right from Aldebaran. The first thing you come to is the House asterism: a pattern of stars like a child’s drawing of a house with a peaked roof. The house is currently upright and bent to the right like it got pushed.

The House includes three easy binocular double stars that form an equilateral triangle, with each pair facing the others. The brightest pair is Theta1 and Theta2 Tauri (the only members of the House that appear on the chart below). You may find that you can resolve the Theta pair with your unaided eyes.

FRIDAY, DECEMBER 27

■ Jupiter is nearly a month past its opposition. That means it’s already fairly high in the east when you first catch sight of it through the fading twilight. How much later in twilight will you first see Aldebaran 6° to its right? And then the 3rd and 4th-magnitude stars of the Hyades V?

Jupiter, and then Aldebaran to its right, appear in the east in the deepening twilight. Jupiter, then Aldebaran, appear in the east in twilight. Orion is rising below them to walk east to west across the sky nearly all night.

■ Right after dark, spot bright Venus in the southwest. Look just 1.1° to its left of for the 3rd-magnitude star Delta Capricorni. Binoculars will help. Although 3rd magnitude sounds easy naked-eye, Delta Cap is less than a thousandth as bright as Venus and less than a finger-width at arm’s length from its glare!

■ As dawn brightens tomorrow morning, look very low in the southeast for the thin waning crescent Moon. Antares is only about 1° to the Moon’s left, and brighter Mercury is 8° to its left, as shown below. Binoculars help.

Antares is magnitude +1.0, while Mercury is magnitude –0.3, three times brighter.

Thin crescent Moon with Antares and Mercury very low in the dawn, Dec. 28, 2024 No, the thin crescent Moon won’t touch or occult Antares; the Moon here is always drawn three times its actual apparent size.

SATURDAY, DECEMBER 28

■ Now Delta Capricorni has moved to glimmer 1.1° below or lower left of Venus right after dark.

■ Unique lineup of Jupiter’s satellites. If you’re in the Eastern time zone, early this evening Jupiter’s satellites will look seriously out of kilter. We’re used to seeing them line up on either side of Jupiter in a more or less straight line with it, like beads on a wire. But at 6:34 p.m. EST, you can catch Callisto, Europa, and Io forming a very straight line that’s canted way out of whack, aiming away from Jupiter entirely!

Jupiter and three moons on 28 Dec 2024

North is up in this simulation of Callisto, Europa, and Io at 23:34 UT December 28th (6:34 p.m. EST). If you live in Europe, this time falls late in the night.Such things can happen because the plane of Jupiter’s orbit is currently tipped slightly to our line of sight, allowing unusual perspectives to be presented to us.

SUNDAY, DECEMBER 29

■ As the year nears its end, Orion has fully come into its own. He’s striding up the east-southeastern sky as soon as it gets dark, with his three-star Belt is nearly vertical. Left of the Belt is orange Betelgeuse and right of the Belt is bright white Rigel, supergiants both.

The Belt points up toward Aldebaran and Jupiter and, even higher, the Pleiades. In the other direction, it points down to where Sirius rises shortly after twilight’s end.

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