Utah Skies: Jupiter In Opposition

Aug 25, 2021

Credit Tom Westre

The following is an unedited transcript:

Jupiter is the largest of the sun’s planets. Like Saturn, Jupiter is a “gas giant” made up of mostly hydrogen and helium gas. In a telescope, you can see the outer layers of Jupiter’s atmosphere defined by its dark bands called belts and lighter bands called zones.

Another atmospheric feature is the Great Red Spot, a raging storm on Jupiter’s surface the size of two Earths. A day on Jupiter is 9.5 hours which makes it a challenge of seeing the GRS.


In 1610 Galileo was the first to observe Jupiter and its four largest moons. Astronomers refer to these moons as the Galilean moons. Each of the moons are different. Io is an active volcanic world, Europa is a bit smaller than our moon, covered with ice and has a liquid water ocean beneath, Ganymede is the largest moon in the solar system larger than Mercury, Callisto is the most distant of the four moons.


You can see the moons move over a period of an hour. At times the moons pass in front of Jupiter and cast a shadow on the planet or pass behind Jupiter. 


On the night of August 19 & 20, Jupiter the King of the planets will be in opposition to the Sun.  Opposition is when the Earth moves between the Sun and Jupiter. When we view Jupiter in our evening sky it will be opposite the Sun. Jupiter is the bright object as it rises in the east in the evening sky and is seen all night long. Jupiter is in the constellation Capricornus and lies just east of Saturn.


For the next few months, happy Jupiter watching.