2024, July 31: Skewered Moon, Jupiter’s Satellites Transit

July 31, 2024: Before sunrise, the moon appears skewered by Tauru’s Elnath. Two of Jupiter’s moon appear to cross the face of the distant planet.

Brilliant Venus and the Crescent Moon, April 26, 2020 — Photo Caption – 2020: April 26: The crescent moon appears near Venus as the brilliant planet approaches the star Elnath.

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by Jeffrey L. Hunt

Chicago, Illinois: Sunrise, 5:44 a.m. CDT; Sunset, 8:09 p.m. CDT. Check local sources for sunrise and sunset times. Times are calculated by the US Naval Observatory’s MICA computer program.

Jupiter’s Satellites Transit

Jupiter's volcanically active moon Io casts its shadow on the planet in this dramatic image from NASA's Juno spacecraft. As with solar eclipses on the Earth, within the dark circle racing across Jupiter's cloud tops one would witness a full solar eclipse as Io passes in front of the Sun. (NASA Photo) — Photo Caption – Jupiter’s volcanically active moon Io casts its shadow on the planet in this dramatic image from NASA’s Juno spacecraft. As with solar eclipses on the Earth, within the dark circle racing across Jupiter’s cloud tops one would witness a full solar eclipse as Io passes in front of the Sun. (NASA Photo)

For sky watchers with telescopes east of Chicago’s longitude, a dance of Europa and Io, Jupiter’s moons and their shadows occurs, where the planet is above the local horizon. The Great Red Spot, a long-lived weather disturbance, is near the center of the planet when the first shadow appears.

Photo Caption – This striking view of Jupiter’s Great Red Spot and turbulent southern hemisphere was captured by NASA’s Juno spacecraft as it performed a close pass of the gas giant planet. (NASA Photo)

Jupiter' Great Red Spot — Photo Caption – Jupiter (NASA Photo)

The planet is very dynamic. Its cloud tops are easily visible through a telescope as well as its four largest moons. Every few days the Red Spot is visible and the planet’s rotation can be noted easily across a few hours. Similarly, the four moons’ orbital motions are easy to see as they revolve around the planet.

When a moon is visible against the planet’s clouds, the event is called a transit. Depending on the direction of sunlight, a moon’s shadow can be seen on the cloud tops.

The shadows and the satellites’ transits begin on the eastern edge of the planet and depart from the globe’s western edge.

Tonight, a double transit occurs with their shadows.

Transit Time Schedule

Jupiter, center, and its moon Europa, left, are seen through the James Webb Space Telescope’s NIRCam instrument 2.12 micron filter. Credits: NASA, ESA, CSA, and B. Holler and J. Stansberry (STScI) — Photo Caption – Jupiter, center, and its moon Europa, left, are seen through the James Webb Space Telescope’s infrared sensors. The Great Red Spot is the bright oval on the lower right of the planet’s globe. (Image Credit: NASA)

Times are listed in Universal Time (UT) and typically designated on a 24-hour clock. Subtract four hours for Eastern Daylight Time, five hours for Central, six hours for Mountain, and so on.

04:20 a.m. UT: Europa’s shadow is first projected on Jupiter’s cloud tops.

04:56 UT: Io’s shadow appears on the cloud tops, a double shadow event.

06:00 UT: Io’s transit begins. About this time the Red Spot is disappearing from view.

06:34 UT: Europa’s transit begins. Two moons and their shadows are seen against Jupiter’s cloud tops.

06:40 UT: Jupiter rises from Chicago. In another hour the planet is visible in clearer air.

06:47 UT: Europa’s shadow leaves the cloud tops.

7:02 UT: Io’s shadow leaves the clouds. A double transit continues.

8:09 UT: Io’s transit ends.

9:00 UT: Europa’s transit ends.

10:44 UT: Sunrise in Chicago

Here is today’s planet forecast:

Morning Sky

Skewered Moon

An hour before daybreak, the crescent moon, 16% illuminated, is 30° above the eastern horizon and 8.3° to Jupiter’s lower left. Look carefully for Elnath, also known as Beta Tauri, 2.2° to the moon’s lower left.

The moon’s placement near the point of a Bull’s horn is a precarious place. The crescent appears skewered by Elnath.

Photo Caption – 2020, July 17: The crescent moon appears near Venus before sunrise. The night portion of the moon is gently illuminated by earthshine.

The moon is exhibiting earthshine, reflected sunlight that gently lights the lunar night.

Jupiter is the brightest starlike body in the sky this morning. It is plodding eastward in front of Taurus, 6.0° to Aldebaran’s upper left, the constellation’s brightest star.

Mars is overtaking Jupiter, 7.1° to the more-distant planet’s upper right and 5.7° to Aldebaran’s upper left. The Jupiter-Mars conjunction occurs August 14^th.

Jupiter Mars in Taurus — Chart Caption – 2024, July 28-August 4: Through a binocular, Mars moves through the same field with Aldebaran and the Hyades star cluster.

The Red Planet is passing the Hyades star cluster. Mars, Aldebaran, and the star cluster appear in the same binocular field of view.

Morning Saturn

Chart Caption – 2024, July 31: Saturn is in the south-southwest before sunrise.

Saturn is the third bright planet in the sky this morning. It is less than halfway up in the south-southwest in front of Aquarius. The starfield is faint and can be seen through a binocular.

Saturn retrogrades, 2024 — Chart Caption – 2024: Saturn retrogrades through a single binocular field of view in front of Aquarius during 2024.

Saturn is retrograding as it approaches opposition on September 7^th. Watch it move westward against the stars until early November.

Evening Sky

Mercury and Venus

Mercury recedes into bright evening twilight, moving toward inferior conjunction – between Earth and Sun – on August 18^th. Then it appears in the eastern predawn sky during September.

Venus slowly emerges from bright evening twilight. It is low in the western sky at 30 minutes after nightfall. Use a binocular.

Evening Saturn

Chart Caption – 2024, July 31: Three hours after sundown, Saturn is in the east-southeast.

Saturn rises less than two hours after sundown. An hour later, it is nearly 15° above the east-southeast horizon. By tomorrow morning it is again in the south-southwest.

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