Astronomy

2020, December 21: Observing the Great Conjunction

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2016, August 27: The Venus-Jupiter conjunction

December 21, 2020:  Jupiter passes Saturn in a close conjunction, known as a great conjunction.  This conjunction is visible from across the globe.  Across the world the planets are visible in the south-southwest after sunset.  This is a slow-moving event that has been unfolding throughout 2020.  This article describes how to observe and photograph this world-wide astronomical spectacular.

by Jeffrey L. Hunt

The December 21 conjunction is a slow-moving event, and on the evening before and after the conjunction, the two planets appear very close together, only slightly farther apart than on the conjunction evening. Watch Jupiter close the gap to Saturn until the conjunction. Step outside after sunset to find them in the southern sky. A binocular is helpful; the pair is visible to the unaided eye as Jupiter overtakes and passes Saturn. On conjunction evening the planets fit into the eyepiece of a spotting telescope or small telescope at low power.

The photo at the top of the page shows an enlargement of the Venus – Jupiter conjunction of August 27, 2016.  The separation of the planets was slightly larger than the Great Conjunction of 2020.  Both planets were close together, but seen as distinctly separate “stars.”

2020, March 2: The morning planets span nearly 18° across the southeast horizon.

The conjunction has been unfolding since Jupiter and Saturn appeared after their solar conjunctions earlier this year.  Then they were visible in the morning sky in the east.  As the year progressed, Jupiter started to close in on Saturn.

For more about the Great Conjunction, read our feature article. This is the closest Jupiter – Saturn conjunction since 1623.

November 29, 2020 Update:  Patrick Hartigan from Rice University has generated a list of Great Conjunctions spanning 3000 years.  The dates may be off a day or two from the actual conjunction dates. His list includes the following close conjunctions:

  • March, 1226, separation 2.1′, one-third the separation of 2020
  • August, 1563, separation 6.8′, slightly larger than 2020
  • July, 1623, separation 5.2′, slightly less than 2020, but not likely visible.

So how do we properly describe this?  Closest since 1623? Yes, although not likely observed.  Closest since 1563?  Yes.  This was easily visible in the morning sky.  Closest observable since 1226?  Yes, this was clearly visible as well. 

2020, May 6: The morning planets span over 28°. The Jupiter – Saturn gap is 4.8°.

By early May, still largely appearing in the sky during the morning, Jupiter closed to within 5° of Saturn.

As Earth approached and passed both planets, they began to retrograde.  This motion is an illusion as our planet overtakes and passes the two planets.

2020, July 20: Saturn and brighter Jupiter appear in the southwest among the stars of Sagittarius. Jupiter is 4.0° to the lower right 56 Sagittarii (56 Sgr), while Saturn is 4.3° to the lower right of Sigma Capricorni (σ Cap).

Earth passed between the sun and Jupiter on July 14. This is known as opposition.  Saturn’s opposition occurred six days later.

2020, September 17: The International Space Station passes Jupiter and Saturn during a 10-second time exposure. The planets are 8.0° apart.

Jupiter’s retrograde ended September 12, while Saturn’s ended September 28.  When Jupiter’s retrograde ended, the gap to Saturn re-opened to 8.1°.

Since early summer, the planets have been visible in the southern after sunset.

2020, November 11: Jupiter is over 23° up in the south-southwest. Saturn is 4.1° to Jupiter’s upper left. The giant planet pair is near 56 Sgr. Jupiter is 3.1° to the lower right of the star, while Saturn is 2.4° to the star’s lower left. Jupiter is 2.5° to the upper left of 50 Sgr.

During mid-November, the planets are in the south-southwest after sunset. They are 3.7° apart on November 15.  They appear in front of the stars in eastern Sagittarius.

2020, November 16: Saturn is 3.6° to the upper left of bright Jupiter. Saturn and Jupiter make a triangle with 56 Sgr. Saturn is 2.6° to the lower left of the star, while Jupiter is 2.4° to the lower right.

It’s easy to watch the progress of the planets as compared to the starry background.  A binocular is helpful to watch this progress, but not necessary.

2020, November 18: The crescent moon is low in the southwest, 6.8° to the lower right of Jupiter. Saturn is 3.4° to the upper left of Jupiter.

The planets are moving eastward compared to a dim star named 56 Sagittarii (56 Sgr on the photos).  With a binocular, the planets’ changing place is easily observed.

2020, November 19: The crescent moon is 5,4° to the lower left of Saturn, while Jupiter is 3.3° to the lower right of the Ringed Wonder.

To the unaided eye, the shrinking gap between Jupiter and Saturn is easily noticed.  On the closest nights, Jupiter and Saturn are visible as individual “stars.”  They do not merge into a single point.

2020, November 26: Saturn is 2.6° to the upper left of bright Jupiter.

Here is a slideshow with images since the planets appeared in the morning sky earlier during 2020.

A tripod-mounted camera with exposures ranging up to 10 seconds can capture the planets and the background stars, as those included in this article. Exposures range from 2.5 to 10 seconds in the above photos.

Cell Phone photo of Jupiter (lower right) and Saturn, November 2, 2020

A smartphone camera, if steadily held, can capture the planets during a typical exposure with no settings changes as the above image illustrates.

Great Conjunction from Santiago, Chile, latitude 33 degrees south.

From the southern hemisphere, Jupiter and Saturn appear in the south-southwest, although Jupiter appears to the upper left of Saturn. Leading up to the great conjunction, observers can see Jupiter approach Saturn, except from the upper left, opposite from northern hemisphere observers.

The chart above, shows the sky from Earth’s southern hemisphere (Santiago, Chile, latitude 33°S) on December 21, 20220, along with the moon and Mars.

2020, December 1: One hour after sunset, Jupiter is 19° up in the southwest, 2.1° to the lower right of Saturn. In the starfield, Jupiter is 2.1° to the lower left of 56 Sagittarii (56 Sgr), while Saturn is 3.7° to the upper left of that star. Additionally, Saturn is 4.5° to the lower right of Sigma Capricorni (σ Cap, m = 5.2).

From the northern hemisphere, on December 1, 2020, the planets are 2.1° apart.

2020, December 7: Jupiter – over 17° up in the southwest – is 3.0° to the left of 56 Sagittarii (56 Sgr). Saturn is 4.2° to the upper left of that star and 3.9° to the lower right of Sigma Capricorni (σ Cap).

By December 7, the gap between the planets is 1.5°.

2020, December 14: the Jupiter- Saturn gap is 0.7°

On December 14, the Jupiter- Saturn gap is 0.7°.  The tip of your pinky finger held at arm’s length fits between the two planets in the sky.

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

On December 16, the crescent moon joins the scene and the planets are 0.5°.  After this evening and until about December 25, your pinky finger covers both planets.

For about the next ten evenings, the planets are close together and are a can’t miss for anybody wanting to see this conjunction.

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

December 21, the Great Conjunction! The planets are closest.

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.

A small telescope (even one used for birdwatching) reveals Jupiter’s four largest moons with and planet and Saturn in the same field of view.

The planets begin to slowly separate.  They appear lower in the sky and disappear into the sun’s glare during early 2021.

Jupiter slowly moves away from Saturn as both revolve around the sun. Jupiter catches Saturn again October 31, 2040.

2020, December 8: Morning Crescent Moon with Leo

December 8, 2020: The thick crescent moon is in the southern sky before sunrise. It is near the star Denebola, the Lion’s Tail. At that time, Venus is in the southeastern sky among the stars of Libra.

2020, December 7: Moon in Leo, Morning Star Venus, Jupiter Nears Saturn

In the morning before sunrise, the slightly gibbous moon is in Leo, between Regulus and Denebola. Brilliant Morning Star Venus is low in the southeast, stepping eastward in Virgo. With the Great Conjunction in two weeks, Jupiter is near Saturn in the southwest after sunset. Mars marches eastward among the stars of Pisces.

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