June 21, 2021: Jupiter begins retrograde, moving westward compared to the distant stars, today. The Jovian Giant, among the stars of Aquarius, is in the southern sky before sunrise.
by Jeffrey L. Hunt
Following Saturn’s lead, Jupiter begins to retrograde this morning. Retrograde motion is an illusion from our planet catching and passing the outer planets.
In the combined motion of Earth and the planets revolving around the sun, the other worlds normally move eastward along the plane of the solar system, the ecliptic. They appear to move in front of the distant constellations that have familiar names, like Taurus and Aquarius, as well as others, such as Cetus and Ophiuchus.
Saturn, over 19° to the lower right of Jupiter, began retrograding in front of the stars of Capricornus on May 22. The planet is slowly moving westward. With a binocular find it to the lower right of the star Theta Capricorni (θ Cap on the chart).
Earth passes between Saturn and the sun on August 2, an event known as opposition. The planet continues to retrograde until October 10 when it resumes its eastward trek compared to the sidereal background.
Jupiter begins its retrograde in Aquarius, near the stars Iota Aquarii (ι Aqr), Theta Aquarii (θ Aqr) – also known as Ancha, “the hip” – and Sigma Aquarii (σ Aqr).
Use a binocular to find the starfield behind the Jovian Giant.
For several days, Jupiter does not appear to move much westward as it begins to pick up speed.
This planet is at opposition on August 19 and ends its retrograde October 17.
Both planets are rising early during the evening, before midnight in Chicago. Saturn rises in the east-southeast nearly 2.5 hours after sunset, about the end of evening twilight. Jupiter follows about an hour later. By one hour before sunrise, both are in the southern sky.
Jupiter is the brightest “star” in the morning sky. Saturn is only dimmer than the Jovian Giant and the stars Arcturus and Vega. By month’s end, Mercury begins to move into the morning sky and becomes the morning’s second brightest “star” during July.
Carefully note the positions of Jupiter and Saturn compared to the starry background during the next few months as they retrograde.
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