Posted by: BibleScienceGuy | June 12, 2019

Jupiter’s Moons in June

(4 Minute Read)

Jupiter and its 4 Galilean Moons
Io, Europa, Ganymede, Callisto
(NASA composite image in top-down order
of increasing distance from Jupiter.)

Have you ever yearned to “discover” Jupiter’s moons, as Galileo did four centuries ago?

If so, now is the time. June is the optimal month of 2019 to view Jupiter and its moons.

Two days ago on June 10, Jupiter made its closest approach to Earth for all of 2019. Jupiter, Earth, and the sun were lined up in a straight line with Earth in the middle. Jupiter was about 398 million miles from Earth, a little over four times Sun’s distance of 93 million miles from Earth.

Jupiter is the fifth planet from the Sun and the biggest one in the solar system with a mass one-thousandth that of the Sun. But its mass is two-and-a-half times the combined mass of all the other planets. Eleven Earths would fit across the face of Jupiter.

Jupiter is the fastest-spinning planet. Its day is only about 10 hours long.

Jupiter is the third-brightest object in the night sky after the Moon and Venus. All month Jupiter will be visible with the naked eye, rising in the southeast at sunset and climbing higher through the night sky before setting in the west at sunrise. The best time to see it is around midnight when it’s highest in the sky.

To help you locate Jupiter in the night sky, here are free Evening Sky Maps. Free monthly sky maps are available on the site for the northern hemisphere, the southern hemisphere, and the equatorial regions.

Jupiter’s Moons

Jupiter’s four largest moons can be seen with a pair of binoculars during June 2019. They are called Galilean moons because these are the moons Galileo saw through a telescope in 1610: Io, Europa, Ganymede, and Callisto (listed in order of increasing distance from Jupiter). Use a tripod, car roof, or tree trunk to help hold your binoculars steady.

Galileo Galilei
Discoverer of Jupiter’s
four largest moons

The four Galilean moons are solid bodies composed of rock and ice — unlike the gaseous Jupiter. They will look like tiny stars on each side of Jupiter. They will be aligned with Jupiter’s equator in almost a straight line because the Galilean moons orbit in the plane of Jupiter’s equator.

On some nights, one or more of the Galilean moons may be hard or impossible to see if they are passing behind or in front of Jupiter. But tonight (Wed June 12), all four Galilean moons will be clearly visible with binoculars. From 10 pm to 2 am EDT, Callisto and Io will be on the left while Europa, and Ganymede will be on the right. Here is an interactive online Jupiter Moons Tool to show the relative positions of the Galilean moons for any date and time from January 1, 1900 to December 31, 2100.

Jupiter has 79 known moons — more moons than any other planet in the solar system. The four Galilean moons are by far the largest. The other 75 known moons and Jupiter’s rings together comprise only 0.003% of the total orbiting mass.

Europa is the smallest of the Galilean moons and Ganymede is the largest. Io and Europa are about the size of Earth’s moon, and Ganymede and Callisto are about 50% larger. Ganymede is the largest moon in the Solar System with a diameter larger than that of the planet Mercury. In fact, Ganymede is 40% of Earth’s size! It would be considered a planet if it orbited the sun instead of Jupiter. Of Jupiter’s 79 known moons, 63 are less than 10 km (6.2 miles) in diameter and have only been discovered since 1975.

Laplace Resonance Animation
Shown by 3 of Jupiter’s Galilean moons.
Color flashes highlight conjunctions.
There are 2 Io-Europa conjunctions (green)
and 3 Io-Ganymede conjunctions (grey)
for each Europa-Ganymede conjunction

The three inner Galilean moons have “synchronized” orbits. For every four orbits by Io (each of which takes 42.5 hours), Europa orbits exactly twice, and Ganymede exactly once. This is called Laplace resonance after the French mathematician Pierre-Simon Laplace (1749–1827) who discovered the relationships of these orbits. Laplace’s mathematical and scientific abilities were so great that he was known as the French Newton.

The most volcanically active object in the Solar System is a moon — Jupiter’s moon Io. It has over 400 active volcanoes. Some of Io’s mountains are taller than Mt. Everest. NASA spacecraft flybys have shown that Io is geologically active with a “young surface with no obvious impact craters.” A “young surface” is what creationists would expect.

There are four moons that orbit Jupiter inside Io’s orbit. These four inner moons and the four Galilean moons all have almost-circular prograde orbits (they orbit in the same direction that Jupiter rotates) in Jupiter’s equatorial plane. The next group of moons are also prograde with elliptical orbits tilted with respect to Jupiter’s equatorial plane. The last group are tilted even more with much more elliptical orbits for the most part. But surprisingly, these are all retrograde, orbiting in the opposite direction of Jupiter’s rotation. How can evolutionary theories of the Jupiter system explain having moons with both prograde and retrograde orbits of many different shapes and tilts? It is impossible for evolutionary theories of the development of the solar system to explain this. It was all set in motion by the Great Creator.

The Great Red Spot in the lower brownish
band is a hurricane about the size of Earth
that has existed at least since the 1600s.


Seeing the Galilean moons move around Jupiter night after night gives one a sense of awe, wonder, and amazement. How did the Psalmist respond to wonders he saw in the heavens?

He responded with praise and adoration for the Great Creator.
The heavens declare the glory of God, and the sky above proclaims his handiwork. (Psalm 19:1)
O LORD, our Lord, how majestic is Your name in all the earth! You have set Your glory above the heavens. 
When I look at Your heavens, the work of Your fingers, the moon and the stars, which You have set in place, 
What is man that You are mindful of him, and the son of man that You care for him?
 (Psalm 8:1,3,4)

This should be our response as well. The wondrous harmony of the heavens should stimulate admiration and praise and honor for the Great Creator.

Moses warned the Israelites not to worship the sun, moon, and stars, no matter how amazing they may be. In fact, the penalty for such worship was stoning (Deuteronomy 17:2-5).
And beware not to lift up your eyes to heaven and see the sun and the moon and the stars, all the host of heaven, and be drawn away and worship them and serve them, those which the Lord your God has allotted to all the peoples under the whole heaven. (Deuteronomy 4:19)

The sun, moon, planets, and stars are created entities. We must be careful to worship the Creator, not any object that He made.

Questions to Ponder

1. Why did God make the planets? What purpose do they serve?
2. Did you see the Galilean moons? How did it enhance your awe of the Great Creator?

Share your thoughts on these questions in the comments below. It could encourage or help another reader.

For Christ and His Kingdom. Soli Deo Gloria.

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©William T. Pelletier, Ph.D.
“contending earnestly for the faith”
“destroying speculations against the knowledge of God”
“for the defense of the gospel”
(Jude 1:3; 2 Cor 10:5; Phil 1:16)
Wednesday June 12, 2019 A.D.

O LORD, our Lord, how majestic is Thy name in all the earth, Who hast displayed Thy splendor above the heavens! … When I consider Thy heavens, the work of Thy fingers, the moon and the stars, which Thou hast ordained; what is man, that Thou dost take thought of him? And the son of man, that Thou dost care for him? Yet Thou hast made him a little lower than God, and dost crown him with glory and majesty! (Psalm 8:1,3-5)

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