Jupiter Close up from Hubble Space Telescope

2020: December 21: The Great Conjunction of Jupiter and Saturn


Jupiter, Saturn, Moon, October 22, 2020
2020, October 22: The nearly first quarter moon, overexposed in the image above, makes a nice triangle with Jupiter and Saturn. The planets are 5.9° apart. The moon is 4.4° to the lower left of Jupiter and 4.2° to the lower right of Saturn.

The Great Conjunction of Jupiter and Saturn occurs on December 21, 2020.  Jupiter passes Saturn in the southwestern evening sky.  This is the closest conjunction of the two planets since 1623.  Jupiter – Saturn conjunctions occur every 19.6 years.

by Jeffrey L. Hunt

On December 21, 2020,  in a close conjunction, Jupiter passes Saturn in the evening sky – known as a Great Conjunction.  Look toward the southwest about one hour after sunset.  The bright “star” is Jupiter.  Dimmer Saturn is immediately to the Giant Planet’s upper right.

Read more about the  planets during October 2020

Once a generation, Jupiter catches and passes Saturn. This is known as a Great Conjunction.  Both planets move slowly around the sun because of their distance from our central star.  A Jupiter year is nearly 12 Earth-years long while Saturn revolves around the sun in nearly 30 years.  A Jupiter-Saturn conjunction is rare enough for observers to take notice of this unique pairing.

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See our detailed article about the Great Conjunction here(updated May 28, 2020)

Jupiter takes nearly 20 years to move past Saturn, travel around the sun, and pass Saturn again.  When Jupiter passes Saturn on December 21, 2020, they will be very close, only 0.1° apart!  This is the closest conjunction since the Great Conjunction of July 16, 1623!  The next Great Conjunction is October 31, 2040, when the two planets are 1.1° apart.  At the next conjunction the planets are low in the east-southeast before sunrise.

November 2020

As viewed from above the solar system, Jupiter passes Saturn in a heliocentric conjunction on November 2, 2020, 49 days before the great conjunction.  The two planets are in along a line that starts with the sun and connects both planets.  As viewed from Earth on this date, Jupiter and Saturn are 5 ° apart.  (See this article for further explanation.)

December 2020

To follow the planet throughout the year, download the daily notes that are linked at the top (current month) and bottom (cumulative index of notes) of this article.  Here’s what to look for during December 2020.

Look low in the southwest, one hour after sunset.  Bright Jupiter is easy to locate.  Dimmer Saturn is nearby, to Jupiter’s upper left.

The moon appears with Jupiter and Saturn on December 16, 2020
2020, December 16. The moon joins Jupiter and Saturn days before the Great Conjunction of 2020.

On December 16, the crescent moon enters the scene. One hour after sunset, the crescent moon (2.3 days past its New phase, 7% illuminated) joins the planets. It is over 6° up in the southwest, about 5° below Jupiter. The Jupiter – Saturn gap is 0.5°.  This is about the apparent diameter of the moon.  Find a clear horizon toward the southwestern sky to find the scene.

Jupiter - Saturn 2020 Great Conjunction
2020, December 21: The Great Conjunction of 2020. Jupiter appears 0.1° to the lower left of Saturn.

Each night thereafter, Jupiter closes on Saturn, until conjunction evening when they are 0.1° apart.  This is close enough to see them in through at a telescope’s low power. Here is the detailed note for conjunction evening:

  • December 21: Jupiter – Saturn Great Conjunction! One hour after sunset, Jupiter is about 12° up in the southwest, 0.1° to the lower left of Saturn. They are 30° east of the sun. Both fit into the eyepieces of modest telescopic powers. Jupiter’s Galilean Satellites are nicely lined up along the equatorial plane of the planet. Ganymede, Io, and Calisto are east of Jupiter, and Europa is west of the planet. Titan is nicely placed to the northwest of Saturn. After the conjunction, Jupiter moves eastward along the ecliptic, separating from Saturn. Each evening the planetary pair appears lower in the sky.
Telescope view of Jupiter and Saturn, December 21, 2020
Jupiter and Saturn are close enough to appear together through a telescope’s low power eyepiece. Saturn’s rings and Jupiter’s four brightest and largest moons are visible as well.

Through a telescope – with an eyepiece that is in the 50x-60x magnification range – Jupiter and Saturn are visible in the same field.  Saturn’s rings are easy to locate.  Jupiter’s four largest and brightest moons – Io, Europa, Callisto, and Ganymede – are evident as well.  On closer inspection, some of Jupiter’s cloud bands are visible.  Some telescopes invert the view compared to the diagram shown here.  Others flip the image left to right.  So the actual view through a telescope may look differently than what is shown here.

The half-full moon is higher in the south-southeast.  Mars is to the left of the moon, over halfway up in the sky in the southeast.  Four bright solar system objects are in the sky – moon, Jupiter, Mars, and Saturn.

Angular Sizes

Moon image by NASA

When viewing the sky, the actual sizes of objects are difficult to determine because there is no depth perception.  We measure objects by their apparent angular size.  Apparent is how large they seem to our eyes.  Angular size is measured in degrees, like the way a protractor measures angles.  The moon appears to be about 1/2° in diameter.  At the Great Conjunction, Jupiter and Saturn are 0.1° apart.  This seems to be close, but they are easily distinguished from each other.  The image above shows the angular size of the moon and 0.1° of angular size on the moon.  The large circular feature is the largest lunar feature, the Imbrium Basin, easily visible without a binocular or telescope.  So the planets are close together, but they do not appear as a “single star” at the conjunction.

Detailed Motion of Jupiter and Saturn

The image at the top of this article shows recent views of the two planets  Notice the separation of the two planets.  At the 2020 Great Conjunction, Jupiter and Saturn are closer than the Venus- Jupiter conjunction of  August 27, 2016 conjunction.

Jupiter and Saturn, their apparent motion in the sky 2020
2020: The apparent motions of Jupiter and Saturn compared to the background stars.

In 1961, the Jupiter – Saturn conjunction occurred in the morning sky, about 2° below 56 Sagittarii. (Note the star’s location on the accompanying chart, nearly 5° west of the Capricornus – Sagittarius border.) The 2020 conjunction occurs about 6° farther eastward, just east of the constellations’ border.

The chart above shows the motions of the planets against the background stars.  Two apparent motions occur to the Bright Outer Planets – Mars, Jupiter, and Saturn.  As Jupiter and Saturn emerge from their solar conjunctions, early in 2020, they appear higher in the sky when weekly observations are made.  They somewhat match the annual westward march of the stars.  This is caused by the earth’s revolution around the sun.  The stars are a calendar.  Over several human lifetimes, the same star is in the same position at the same time and same date each year.

The second motion is a combination of the planets’ slow orbit around the sun, especially for Jupiter and Saturn, since they don’t appear to move far during a year and Earth.  Jupiter and Saturn appear to move eastward (direct motion) compared to the starry background.  During the next year they are among a faint starfield in eastern Sagittarius and western Capricornus.  As our planet catches up and passes between them and the sun (opposition), they appear to move westward (retrograde motion) compared to the stars — retrograde motion.  After Earth passes them, Jupiter and Saturn seem to resume their direct motion compared to the background that moves farther west and rise earlier as the seasons progress.

Jupiter finally catches Saturn in late December for this Great Conjunction. On the chart, notice that Mars passes Jupiter and Saturn during late March 2020.

Read about the 1623 Jupiter – Saturn Great Conjunction here.

Monthly Summaries of What to Watch

(Bookmark this page to return for monthly updates of the planets’ locations.)

Recent Jupiter and Saturn Articles

Moon in the Bull's Horns. October 8, 2020

2020, November 3: Morning Star Venus, Mercury and Moon, Bull’s Horns


Mercury begins to join Morning Star Venus in the eastern sky before sunrise. The moon is in the morning sky in the west. Three evening planets are found after sunset, Mars, Jupiter, and Saturn. Mars is in the east-southeast and the Jupiter – Saturn pair is in the south-southwest after sunset. Four hours after sunset, look for the moon between the bull’s horns.

Crescent Moon, Venus, and Aldebaran, July 17, 2020

2020, November 2: Morning Star Venus, Mercury and Evening Planets


Mercury begins to join Morning Star Venus in the eastern sky before sunrise. The moon is in the morning sky in the west. Three evening planets are found after sunset, Mars, Jupiter, and Saturn. Mars is in the east-southeast and the Jupiter – Saturn pair is in the south-southwest after sunset. Today is a heliocentric conjunction for Jupiter and Saturn.

Venus and Moon, October 13, 2020

2020, November 1: Speedy Mercury, Evening Planets


Speedy Mercury joins Morning Star Venus in the eastern sky before sunrise. The first rock from the sun is entering the morning sky for its best appearance of the year. In the evening, Mars shines in the eastern sky, while in the south-southwest Jupiter edges toward its Great Conjunction with Saturn on December 21, 2020.

Recent Articles

Mars
Mars (NASA Photo)

2020, Mars During November


The Red Planet’s retrograde motion ends during mid-November. The planet slowly resumes its eastward direction among the dim stars of Pisces. Bright Mars is visible in the east-southeastern sky after sunset during November.

Venus and Moon, October 13, 2020
2020, October 13: The moon (26.0 days past New moon phase, 16% illuminated) – nearly 33° up in the east – is 8.8° above Venus, 24.0° up in the east. The crescent is 5.9° to the lower left of Regulus.

2020, November: Brilliant Morning Star Venus and Mercury


Brilliant Venus continues to shine brightly in the morning sky. Venus is “that bright star” in the southeastern sky before sunrise. Venus steps eastward in Virgo as Mercury makes its best morning appearance for the year. The crescent moon joins the bright inner planets on November 12 and November 13.

Jupiter and Saturn, July 17, 2020
2020, July 17: Bright Jupiter (lower right) and Saturn shine from the southwestern sky.

2020, October 26: Morning Star Venus, Evening Moon, Planets


Brilliant Morning Star Venus shines in the eastern sky among the stars of Pisces. Mars is visible earlier in the morning, but is low in the sky when Venus rises. In the evening, Mars shines from the east, while Jupiter and Saturn are in the south-southwest as a prelude to their Great Conjunction on December 21, 2020. The moon appears to the upper right of Mars.

2 thoughts on “2020: December 21: The Great Conjunction of Jupiter and Saturn”

  1. Sky & Telescope’s SaturnMoons app on my iPhone shows both Saturn and its moons and Jupiter and its moons during the great conjunction. I found this out when I pinched the scene to zoom out. The Jupiter moons app doesn’t have this ability.

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